Calculate Your Enclosure Here
This calculator will design an enclosure using any value for F3(L) that you desire. If the "Gain" value comes up negative, you will have to increase the value you entered for F3(L), or choose a higher S factor. Note : Too much gain can be hazardous to your speakers, try to keep it +3 dB or less unless you want to find out what your speakers look like with holes in them. If the calculated gain is too high, enter a lower number in the desired F3(L) box. If the gain returns a negative value, enter a higher F3.
Number of Drivers	Isobaric Loading Yes  No

Enter Qts Enter Vas  (ft3 ) Enter Fs

Choose an S Factor 0.7  0.6   0.5

Enter Desired F3(L)

Vf =(ft3 ) Vr = (ft3 )

Qbp =  Fb = Hertz

Passband =  Hertz Gain = (dB SPL@1W/1M)

Instructions

1. Make sure you have Java turned on in your browser.
2. Enter required information.
3. Click "Calculate" to get the answers.
4. The calculators will give accurate results only for rectangular shaped objects.
     

Calculators

1. Box Dimensions Calculator: Figures out third dimension of a box, given two known dimensions, required internal volume and material thickness.  For example, if you have the length and height of a part of your trunk, and need to figure out the width of the box: Enter the two dimensions you have measured, enter the internal volume, and the thickness of the wood.  If you are placing objects inside the box, such as braces, or a piece of wood to separate the box into two independent boxes for two woofers, use the "Solid Object Volume Calculator."
     
2. Solid Object Volume Calculator: Figures out volume of an object to be placed inside a box. Then add result to "required internal volume" in the "Box dimensions Calculator".
     
3. Conversion Factors: Metric to English units, Cubic inches to cu ft, etc.

Box Dimensions Calculator

Solid Object Volume Calculator

Conversion Factors

This page contains descriptions of the variations in port designs used in speaker enclosures.  The most common type of port is a round tube. These are typically made of black plastic and look like a section of thin-walled pipe with a lip on one end.  The second most frequently used type of vent is a square port. The advantage of this design is that you are not limited by availability of only certain diameter tubes. You can also build the port out of the same material you are using to fabricate the enclosure.  The last type of vent is called a slot port. It is created using one wall of the enclosure as a wall of the vent. This can be very useful for bandpass enclosures which can be very hard to tune to a low enough frequency due to the small size of the front (vented) chamber. Friction created by the air flow in the enclosure traveling along the enclosure wall makes this type of port effectively longer than it physically is - which tunes the enclosure to a lower frequency so a slot port will be shorter for the equivalent vent area when compared to a simpler square vent. Porting tips: Keep the port(s) as far away from the enclosure sides and back as possible except for the slot type port. Make sure the inside end of a tube or square port is at least the equivalent of one vent diameter away from the back of the box or any bracing materials. Keep the vent free from anything that may affect air flow through it. The port should also be placed as far away from the speaker cone as practical.

Sixth-Order Bandpass Subwoofer Enclosure Design Calculator

Explanation of Terms

Qts, Vas, and Fs, are the electro-mechanical parameters for your woofer. They are also commonly referred to as the "Thiele-Small" parameters. You can get these from the paperwork that came with your speakers, from the dealer where you purchased your speakers, or from the manufacturer of the speaker (they are sometimes hard to contact, however).

F3(L) - the frequency where the response is down by 3 dB (on the low end of the passband). This will be the first number in the "Passband" box when you calculate an enclosure.

F3(H) - the frequency where the response is down by 3 dB (on the high end of the passband). This will be the second number in the "Passband" box when you calculate an enclosure.

Vf - the internal volume of the front chamber of the enclosure.

Vr - the internal volume of the rear chamber of the enclosure.

Fb(F) - the frequency that the vent in the front chamber of the enclosure needs to be tuned to.

Fb(R) - the frequency that the vent in the rear chamber of the enclosure needs to be tuned to.

Passband - refers to the range of frequencies that will be allowed to pass through the speaker system (the frequencies you will be able to hear/feel). Any frequencies above or below the passband will be attenuated (reduced).

Gain - the amount of boost(or in some designs the amount of attenuation) in sound pressure level(SPL). This is usually referred to in speaker design with other terms, which serve to make it a valid reference point. A typical specification for a bandpass enclosure would be : Efficiency/Sensitivity : 94 dB @ 1W/1M.  This means that this design is capable of creating a sound pressure level of 94 dB when a signal of 1 watt is applied to it, and is measured with the measuring instrument 1 meter (approximately 3.28 feet) away from the speaker system.

Typical Sixth-Order Bandpass Enclosure Design

This style of enclosure is patented by the Bose Corporation, information provided is for personal use only.

Calculate Your Enclosure Here
One of the reasons bandpass enclosures are so popular is because of an inherent property they have that allows the enclosure designer the flexibility to trade bandwidth for efficiency and vice versa. This calculator will design a 6th order bandpass enclosure. This calculator is only for Qts values from 0.18 to 0.28.
To use this calculator, enter your values for Qts, Vas, and Fs, and then click the "Calculate Enclosure" button. Your results will appear in the other boxes. Note : Too much gain can be hazardous to your speakers, try to keep it +3 dB or less unless you want to find out what your speakers look like with holes in them.
Number of Drivers	Isobaric Loading Yes  No

Enter Qts	Enter Vas  (ft3 )	Enter Fs
Vf = (ft3 ) Vr =  (ft3 )	Fb(F) = Hertz Fb(R) =  Hertz	Passband =  Hertz Gain = (dB SPL@1W/1M)

Vent Dimensions Calculator
Formulas
Minimum Usable Vent Diameter
The first thing you should do when calculating a vent is to determine how big it has to be. "Port noise" can ruin the sound of an otherwise good enclosure design. If you do not have the Xmax figure for your driver(s), leave the default value (it is an average value suitable for most subwoofers).  If you want to use this calculator, first choose what size driver(s) you are using, then enter how many are in your enclosure. Now, enter your Xmax figure (in millimeters), and the frequency that you need to tune your vent to. And, finally click the "Calculate Minimum" button to get your results. The "Minimum Diameter" box is for round ports, and the "Minimum Area" box is the minimum area required for a square vent. If you need to convert a measurement to/from English/Metric click here, then come back.
Driver Size (Inches) 6.5 8 1012 15 18	Is this a bandpass enclosure? No  Yes
Enter Quantity of Drivers  Enter Xmax mm Enter Tuning Frequency Hertz	Minimum Diameter =  inches Minimum Area = inches Length of a side for a square vent = inches

Calculate Your Vent Length
To use this calculator, first you will need to choose whether you want a round or a square port. Then, enter your internal box volume (in cubic feet).  Next, you enter either an inside diameter for the tube you are using if you want a circular port, or the inside dimensions of the square port you are going to build into your box (make sure you click the "Slot Port" button if you are designing a slot port - if you don't understand the difference between a square vent and a slot vent, click here). And finally, press the "Calculate Length" button at the bottom, and your answer will appear in the "Vent Length" box.
Select Your Port Type Round  Square	Is this a slot port ? No  Yes
Quantity of ports Enter Enclosure Volume (ft3 ) Enter Desired Tuning Frequency  Hertz
Round Vent Enter Desired Port Diameter  Inches	Square Vent Enter Height  Inches Enter Width Inches
Vent Length  Inches
If you come up with a value too long for your enclosure, enter a smaller number(s) for the diameter, or the heighth/width of your vent(s), and click the "Calculate Length" button again to recalculate (you don't need to reload the page).

Sealed Speaker Enclosure Design Calculator
This calculator is designed to tell you the Qtc of a sealed enclosure. It is useful for determining how a different woofer will function in an existing box (for example - if you ruined a speaker and a replacement is unavailable), or if you know your speaker parameters and just want to find out what the Qtc value of your speaker system is.  If you don't understand anything on this page, click here to learn the basics of "sealed" speaker enclosure design.
Calculate Your Qtc Here
To use this form, enter the Qts, Vas, and Fs parameters for your speaker, and then enter your enclosure volume (Vb) in the boxes below. Then click the "Calculate Qtc" button, and the results will appear in the empty text boxes.
Enter Qts Enter Vas  (ft3 ) Enter Fs Hertz Enter Vb (ft3 )	Qtc =  Fc = Hertz F3 = Hertz

Check with manufacturer or dealer for appropriate box volume and design.  Some subs can't be used in certain types of boxes, and have very small tolerances for box volume errors.  If a sub is installed in a box larger or smaller than what is supposed to, it will sound bad and could be destroyed.  Boxes can be built in any shape, but it is difficult to calculate volume for complex shapes.

Materials

A box has to be very rigid.  Most common building materials are 5/8" or thicker particle board or medium density fiberboard.

If building a box with Plexiglas, do not use anything less that 1/2 inch thick.

A common material used to mold complex shaped boxes is fiberglass, but it is a real pain to work with, and several layers need to be applied for a solid finish.

Gluing, Sealing

Use glue at all joints (cheapest and most used product is Liquid Nails).  Make sure there are no holes.  Any leaks will degrade the performance of your subs, not to mention the annoying noise air makes when being pushed out of a small hole.

Let glue cure for at least 24 hours before mounting the woofers.  The fumes of some products will eat up rubber and other materials subs are made of.

Holding Joints Together

Screw joints (use 2"  -  2-1/2" screws) every four inches or so. Pre-drill about 3/4" deep, so that screws do not split the wood at the edges, especially when working with particleboard.

A box for Each Sub?

Even though it is not necessary to have two separate chambers for two subs, it is best to take this approach for two reasons:  First, if one of the subs dies, then the volume of the box will be "twice" as big, as seen by the sub that is still working.  This could cause problems and even damage the other sub.   The second reason is bracing.  building a box with a divider in the middle will be much sturdier.

Making Ports

There are several way to build ports.  If a pre-made port is not available, the most common material is PVC tubing.  PVC tubing is very rigid, comes in different diameters, and is easily found at any hardware store.

Cut the tubing at the desired length.  Consider the volume the port takes up when calculating the box volume.  Cut a hole in the box.  Make sure the hole is as perfect as possible to minimize gaps between the box and the tube.   A couple wood braces can be added for screwing the port top the box.  Seal the gaps using plenty of Liquid Nails or similar product.

Bracing

Boxes that are more than a foot on width or length or height, should be braced (use a piece of wood maybe 3 or 4 inches wide across the box, so that box does not flex).  It is a good idea to put wood blocks on the corners for reinforcement. Always consider that blocks, braces, neon lights, etc. inside a box take up space and should be accounted for when calculating internal volume.

Damping/Filling

It is advisable to put damping material inside a box.   Pillow polyfill and fiberglass insulation are common, though polyfill is a lot easier on your skin.  This increases subwoofer efficiency by dissipating some energy that affects the sub, particularly the voice coil.  Polyfill also "fools" a sub into thinking it is in a bigger box.  Play around with different amounts of polyfill until you get the desired results.

Finishing the Box

Add wood filler to holes and sand the box to make a smooth surface.  If you are painting the box, It is a good idea to apply primer under the paint.

It is not necessary to sand the box if you are using carpet or padding under vinyl, since the thickness of the material will cover any small imperfections.  The best way to cut carpet or vinyl is with a good quality carpet knife.  Blades wear out pretty quickly, so buy a handful.  Cut a piece of carpet (or vinyl) big enough to cover the whole box.  Apply adhesive to both box and carpet (spray 3M adhesive 77 or 90 works great). Wait about a minute and place the fabric over the wood.  For a good fit, stretch the fabric when applying it.   The fabric should wrap around and end in a place of the box that will not be seen.  Do one side at a time, cutting excess carpet.  If possible, add staples to hold the fabric at the ends.

Calculate Your Enclosure Here
This Javascript™ is designed to calculate a bandpass enclosure with any amount of gain that you desire. If the F3L is too high, try a higher S factor. If this still gives you a F3L that is too high, you will have to reduce the amount of gain you are asking for, or use a different speaker. Note : Too much gain can be hazardous to your speakers, try to keep it +3 dB or less unless you want to find out what your speakers look like with holes in them.
Number of Drivers	Isobaric Loading Yes  No

Enter Qts Enter Vas  (ft3 ) Enter Fs

Choose an S Factor 0.7  0.6   0.5

Enter Desired Gain  dB

Vf =(ft3 ) Vr = (ft3 )

Qbp =  Fb = Hertz

Passband =  Hertz

Sealed Speaker Enclosure Design Calculator
This calculator will design a "sealed" speaker enclosure to obtain a specific Qtc value. If you don't understand what this means, click here for help.
Calculate Your Enclosure Here
To use this form, enter the Qts, Vas, and Fs parameters for your speaker, and then enter your desired Qtc in the boxes below. Then click the "Calculate Enclosure" button, and the results will appear in the empty text boxes. If the calculated F3 (-3 dB point) is too high you will need to enter a lower value for desired Qtc. A Qtc value of 0.707 will give you the lowest possible F3 for the woofer or subwoofer you are using. This is a maximally flat alignment. The drawback is a larger enclosure. F3 increases for Qtc values higher than 0.707, below that it increases again.
Note: Typical Qtc values for designs that are commonly available are from 0.9-1.2. This means that most designs you have heard (unless you are listening at high-end audio retailers) are likely to have a peak in frequency response in the 70-120 Hz range. Many people like this and will be disappointed by the sound of a speaker without this "boost" in the bass.
Number of Drivers :	Isobaric Yes  No
Enter Qts Enter Vas  (ft3 ) Enter Fs Hertz Enter Qtc	Vb =  (ft3 )  F3 = Hertz
If you want to experiment with different quantities of drivers, or the isobaric option, you  don't need to enter the values again, just change the value you want to adjust and click the "Calculate Enclosure" button again.

Sealed Rear Chamber Bandpass Sub Woofer Design Tips

Explanation of Terms

Qts, Vas, and Fs, are the electro-mechanical parameters for your woofer. They are also commonly referred to as the "Thiele-Small" parameters. You can get these from the paperwork that came with your speakers, from the dealer where you purchased your speakers, or from the manufacturer of the speaker (they are sometimes hard to contact, however).

S Factor - refers to the efficiency of the enclosure. 0.7 is the most efficient, however, it also has the narrowest passband. 0.5 is the least efficient, but it has the widest passband. Another drawback to the lower S Factor designs is that they have more passband ripple  (the sag in the frequency response plot in Figure 1). Higher S factor enclosure designs also exhibit better transient response.  One of the reasons bandpass enclosures are so popular is this inherent property that allows the designer the flexibility to trade bandwidth for efficiency or vice versa.

Figure 1

F3(L) - the frequency where the response is down by 3 dB (on the low end of the passband   - see Figure 1). This will be the first number in the "Passband" box when you calculate an enclosure.

F3(H) - the frequency where the response is down by 3 dB (on the high end of the passband  - see Figure 1). This will be the second number in the "Passband" box when you calculate an enclosure.

Vf - the internal volume of the front (vented) chamber of the enclosure.

Vr - the internal volume of the rear (sealed) chamber of the enclosure.

Qbp - is the total resonance of the speaker system. Essentially the same as Qtc is in a sealed design.

Fb - the frequency that the vent in the front chamber of the enclosure needs to be tuned to.

Passband - refers to the range of frequencies that will be allowed to pass through the speaker system (the frequencies you will be able to hear/feel). Any frequencies above or below the passband will be attenuated (reduced).

Gain - the amount of boost(or in some designs the amount of attenuation) in sound pressure level(SPL). This is usually referred to in speaker design with other terms, which serve to make it a valid reference point. A typical specification for a bandpass enclosure would be : Efficiency/Sensitivity : 94 dB SPL @ 1W/1M.  This means that this design is capable of creating a sound pressure level of 94 dB when a signal of 1 watt is applied to it, and is measured with the measuring instrument 1 meter (approximately 3.28 feet) in front of the speaker system.

Typical Fourth-Order Bandpass Enclosure Design

General Design Tips

Always add the volume displaced by the speaker's motor system (the magnet, frame, and the suspension), and all bracing materials to your enclosure's rear chamber volume when designing a speaker system.  If you add damping material (fiberglass, Acousta-Stuf™ polyfill, Dacron™, etc...), you can design the rear chamber of your enclosure 10% smaller than the suggested ideal size. I usually use 3/4-1 lb. per cubic foot (polyfill) of enclosure volume. I prefer not to use fiberglass because there is a chance that the fibers can get in the voice coil, and also because of the health hazards (skin & lung irritation) that are possible when working with this material.  You should also take the volume consumed by your port(s) into account when designing the front chamber of your bandpass enclosure (unless you're designing an enclosure with the vent on the outside of the box).  Some people feel that because a bandpass enclosure naturally attenuates the higher frequencies a lowpass filter is unneccessary, this is false. Bandpass enclosures create standing waves in the front chamber of the enclosure which cause peaks in the frequency response. In my opinion, sub woofers sound much better when they are not receiving any high frequencies. So, always use a lowpass filter (or a notch filter) on any bandpass sub woofer design.  I do not put damping material in the front chamber of bandpass enclosures because it can shift around in the enclosure and interfere with vent operation unless it is very securely attached. I do however, cover all of the interior walls of the front chamber with carpet underlayment (padding - put the hard side toward the wood if the type you get has a side with a sealing layer on it). I believe this helps to suppress the standing waves created in the front chamber. I have also heard that felt works well when used in this application - I have never tried it though.  Before you attach the last panel of your enclosure, apply silicone to all of the joints in the enclosure, and also seal the back of any wiring terminal cups (if a gasket was not provided with it). Let the silicone fully cure (read the label and follow all of the instructions) before putting on the last panel. I install the damping material at this time while waiting for the silicone to dry.

Build your enclosure using the thickest, hardest, non-resonant material you can get your hands on. I use 3/4" (minimum) medium density fiberboard (MDF). Solid wood is not a good choice for enclosure construction - although hardwoods do make excellent bracing material. You can use some types of plywood - it has to be marine grade though (which can be expensive). The last choice is particle board - this material is flimsy and it is hard to make solid enclosure joints with, but if you cannot get MDF in your area you can use this (brace the enclosure very thoroughly if you do).

For some excellent advice on bracing your speaker enclosure, click here.

Minimum Vent Diameter

The first two formulas shown here represent the minimum usable port diameter for subwoofer speaker enclosures - they are set up to avoid power compression and vent noise. The first one is the one I use for bandpass designs (from "The Loudspeaker Design Cookbook" by Vance Dickason - I divide the tuning frequency by two before I use it in this formula though), and the second is a more conservative formula from the works of Richard Small, which is useful for vented speaker designs.

dv - is the required diameter of the port in inches.

Fb - is the tuning frequency of your enclosure in Hertz.

Vd - is the volume displaced by the driver (in cubic meters) traveling through it's full excursion (peak-to-peak). To figure out Vd for a speaker, find the Sd value for your driver in the table below, and multiply that number times the Xmax (in meters) of your speaker.

Driver Diameter Sd (M2) 18" 0.1300 15" 0.0890 12" 0.0530 10" 0.0330 8" 0.0220 6.5" 0.0165 6" 0.0125 5.25" 0.0089

Vent Length

This formula is also from "The Loudspeaker Design Cookbook". It tells you how long you need to make the vent.

Fb - is the tuning frequency of your enclosure in Hertz.

Lv - is the length of your port in inches.

R - is the inside radius of your vent tube.

Vb - is the internal volume of your enclosure in cubic inches. To convert cubic feet to cubic inches, multiply by 1728.  If you want to use multiple ports, divide your enclosure volume by the number of ports you want to use, then use the result of this calculation as your Vb in the formula below to find out how long each port should be (a tip from JL Audio™).

If you want to calculate square vents, the formula below will give you the value of R to use in the formula above.

In the formula above, a is the area of your square vent (height x width), and  (Pi) is approximately 3.141592.

Butterworth Fourth-Order Vented Speaker Enclosure Design Formulas & Calculator

Explanation of Terms

Qts, Vas, and Fs, are some of the electro-mechanical parameters for your woofer. They are also commonly referred to as the "Thiele-Small" parameters. You can get these from the paperwork that came with your speakers, from the dealer where you purchased your speakers, or from the manufacturer of the speaker (they are sometimes hard to contact, however).

Vb - the required internal volume of the enclosure.

F3 - the frequency that the response is down by 3 dB at.

Fb - the frequency that the vent needs to be tuned to.

Enclosure Design Formulas

Typical Vented Enclosure Design

Vb = Qts 2.87 x 15 x Vas

Fb = Qts -0.9 x 0.42 x Fs

F3 = Qts -1.4 x 0.26 x Fs

Calculate Your Enclosure Here
To use this form, enter the Qts, Vas, and Fs parameters for your speaker in the boxes below. Then click the "Calculate Enclosure" button, and the results will appear in the empty text boxes.
Number of Drivers :	Isobaric Yes  No
Enter Qts Enter Vas  (ft3 ) Enter Fs Hertz	Vb = (ft3 ) F3 =  Hertz Fb =   Hertz
If you want to experiment with different quantities of drivers, or the isobaric option, you  don't need to enter all of the values again, just change the value you want to adjust and click the "Calculate Enclosure" button again. When you are finished, write down your enclosure specifications, (or copy & paste them), and go here to design your port.

This page is designed to help you determine the proper dimensions for a speaker enclosure. There are some ratios which are typically used to determine an enclosure shape that will help to minimize standing waves in the familiar rectangular speaker box. Never build a cube shaped box, which is the absolute worst enemy of a smooth frequency response curve.

The "Golden Ratio"
To use this calculator, enter the volume of your enclosure (in cubic feet) in the first box. Then click the "Dimensions" button to see the proper internal dimensions for your new speaker box design.
Box volume =  (Ft3)	Depth = inches Height =  " Width = "
Total =  (Ft3)
Due to rounding, the total number shown above will come out smaller than the value you entered. This is normal. This calculator is only intended to give you some "ballpark" figures to use in the calculator below.

 

The Actual Box
To use this calculator, add a little bit to the dimensions from the calculator above. Then click the "Box Volume" button to see the volume obtained from these dimensions. You won't need to re-enter all the values to re-calculate, you can change only one or as many as you desire. Then click the button again to calculate another time. Inch Measurement Decimal Equivalent 1/16 0.0625 1/8 0.125 1/4 0.250
Depth = inches Height =  " Width = "	Box volume =  (Ft3)
Due to rounding, the total number shown above will come out smaller than the value you entered. This is normal. This calculator is only intended to design a speaker box with the correct proportions in an easy to build shape.

Calculating Vent Air Speed
This calculator is intended to help you determine the speed of the air in a port. This will help you decide if a particular port is too small for your application, which will cause noise at high volume levels. This is not intended for use on bandpass designs. The answer is in percentage of the speed of sound. If you don't need to know the air speed in the vent, click here to automatically calculate a port that is the proper size for your speaker enclosure.
A general rule regarding port air speed is to try to keep it 10 percent or less of the speed of sound.
Explanation of Terms
W is the acoustic power output of the speaker in Watts. You can calculate this by multiplying the reference efficiency times the power handling of the speaker. Fb is the tuning frequency of the enclosure. R is the radius of the port. Mach is the speed of sound in air (344.8 m/sec or 1131.2 ft/sec).
Calculate
To use this form, enter the values for W, Fb, and port radius. Then click the "Calculate Values" button, and the answer will appear in the empty text box.
Enter W Enter Fb Hz Enter Radius  inches	percentage of Mach

Sealed Speaker Enclosure Design

Explanation of Terms

Qts, Vas, and Fs, are the electro-mechanical parameters for your woofer. They are also commonly referred to as the "Thiele-Small" parameters. You can get these from the paperwork that came with your speakers, from the dealer where you purchased your speakers, or from the manufacturer of the speaker (they are sometimes hard to contact, however).

Qtc - is the total resonance of the speaker system. An enclosure with a Qtc value of 0.707 will give you the flattest frequency response and the lowest possible F3 for a given driver, use this value if you want the your music to sound as close to the original recording as possible.  In the frequency response plot below, the relative efficiency of the speaker is 90 dB. So,   the frequency of F3 is determined by first finding the proper SPL (sound pressure level) to look at (90 dB - 3dB = 87 dB) on the left scale, and then following this line over to the right until you run into the frequency response plot (the colored lines) of the enclosure you are interested in. Then you draw a line from this point down to the bottom scale to find the frequency of F3.  Most people like the sound of boxes designed with Qtc values ranging from 0.9-1.1 which produces a slightly emphasized bass range. Values above 1.2 are undesirable because they tend to sound unnatural (the peak around the 100 Hertz range in the plot above is what most people refer to as "boomy" sound), and they also can be physically hard on the speaker. Important Qtc relationships :  F3 increases for values above or below 0.707.  Enclosure volume (Vb) requirements decrease with higher Qtc values.  Mechanical power handling increases for Qtc values up to 1.1 .  Mechanical power handling is not the same as the manufacturers' "power rating" (which only tells how much power the voice-coil can handle without burning up, and has nothing to do with how much input power the speaker can take before it bottoms out). The speaker's suspension and the enclosure design determine the mechanical power handling of the system.

Fc - the resonant frequency of the driver when mounted to an enclosure.

Vb - the required internal volume of the enclosure.

F3 - the frequency that the response is down (from the reference level) by 3 dB at. In the frequency response plot below, the reference level is 90 dB (left scale). So, the frequency (bottom scale) of F3 is at the intersection of 87 dB and 40 Hertz. Therefore, this enclosure design has an F3 of 40 Hertz.

- The Greek letter alpha. In speaker design, this term is used to reflect the ratio of speaker compliance (Vas) to enclosure volume (Vb).

Second-Order Speaker Enclosure Design Formulas

Typical Sealed Enclosure Design

The following formulas will allow you to design a sealed speaker enclosure for any Qtc value you desire.

= (Qtc / Qts)2 - 1

Vb = Vas /

Fc = (Qtc x Fs) / Qts

If you don't want to/can't calculate an enclosure using the formulas shown above, click here to use the Javascript™ calculator, which does all of the math for you.

An introduction To Amplifiers!

Amplifiers take the signal from the head unit and makes it large enough to be able to drive your speakers. It is preferable to use separate amps for high and low frequencies but it is not necessary. The problem with using one amp for all frequencies is that you cannot adjust the levels among different frequency ranges as easily as you can adjust outputs of separate amps. Many people start their system with an amplifier for the low frequncies (bass) and use their head units built-in power to drive the higher frequency speakers. This is adequate but the built-in power in a head unit is usually not strong enough for high volume listening and not clean enough for the discerning ear. There are many options when choosing an amplifier.

Power?
There are different ways in which power is measured by amplifier manufacturers to make people think that their amps have more power than others. Laws of physics tell us that Power can be obtained by multiplying Current and Voltage. For example, if your amplifier gets 12 volts, and it draws 20 amps, then power would be 240 watts, right? Not exactly. In the real world, amplifiers waste 50% or more of the power in the form of heat. That leaves you with only 120 watts.

Click to View

Things get more complicated than that. There are different ways to measure power. Power can be measured for top to bottom of the signal (Peak, or Max, etc). Another way to measure power is From the zero-level to the top half (usually called music power). The most accurate way to measure power is RMS (root mean square) watts. The RMS value is obtained by squaring the value of the signal, taking the average, then the square root. This is the equivalent of the actual power delivered. Most reputable manufacturers use the RMS rating.

To get RMS power from peak or max power just divide by three. Music power is just half of peak power. For example, an amplifier is rated at 100w (peak) per channel. The so called Music power would be only 50w per channel. The RMS power would be 33w per channel. Big difference, isn't it? Be careful when checking specifications of amps before buying, to see what you are really getting. Always ask for the RMS power of an amplifier.

Confused enough? There is more. Some companies rate their amplifiers using unrealistic conditions, for example calculating power at 15 volts, under 2 ohms, at 10% distortion, etc. Make sure you see the actual test voltages and loads.

How to tell if I am getting a good amp?
Shop for reputable brands. Look at the size, weight of the amp. The more power the amp puts out, the more wasted heat, and the bigger area it will need to dissipate that heat (bigger heatsinks). This alone can't be enough to determine if the amp is good or not. Watch out for companies that use bigger heat sink than needed, giving the idea of a more powerful amp.

Look at the fuses that are either plugged into the amp, or specified by the instruction book. If you see a 400w amplifier with a 5-amp fuse, you should be suspicious. Remember what was said above, multiply size of the fuse by around 6 (12v at 50% efficiency), and that will give you a rough idea of what you are dealing with in terms of maximum possible RMS power.

How much power do I need?
For mids and highs, anywhere from 30 to 50 watts (RMS) per channel would be a minimum. For subs you would need at least 80 - 150 watts (or more) per subwoofer. There should always be more total power going to the subwoofers than  the rest of the speakers, since human ears are more sensitive to higher frequencies than lower. For example, if you have 4 x 50 watts going to all your mids and tweeters (total=200 W), then you should have at least 200 W or more going to your subs.

A lot of people wonder if too much amplifier power can burn up the speakers. What damages speakers most of the time is distortion, not power. If the speakers have the proper crossovers and are not distorting, then it is really hard to blow them. A bigger amp just gives you the opportunity to go to higher volumes without distortion.   Get the biggest amplifiers you can afford and your car's electrical system can handle.  More power means louder sound, but most importantly, cleaner sound.

What Else to Look For in an Amplifier

It is a good idea to get an amp with a built-in crossovers, so that you don't have to spend extra money later on crossovers. If you are going to be using multiple speakers, make sure the amp is 2-ohm stable (or less). A bridgeable amplifier could come in handy in the future if you are planning to upgrade. Overheat, short-circuit, overload protections are good features that any good amplifier should have.  Look for a low THD (total harmonic distortion) rating.

Amplifier Classes
There are different amplifier designs: Class A, A-B, B and D

Class A amplifiers are the most sonically accurate. On the other hand, they have some drawbacks that make them a rare breed. Class A amplifiers use only one output transistor that is turned "on" all the time, giving out tremendous amounts of heat. Class A amplifiers are very inefficient (less than 25%). More heat means more heatsink area, so even though most class A amps have built-in cooling fans, they are big.  Class A amplifiers are usually and expensive choice.

Class B amplifiers are the most common by far.  They use two output transistors. One for the positive and one for the negative part of the cycle. Both signals are then "combined". The problem with this design is that at the point when one transistor stops amplifying and the other one kicks in (zero volt line), there is always a small distortion on the signal, called "crossover distortion". Good amplifier designs make this crossover distortion very minimal. Since each transistor is "on" only half of the time, then the amplifier does not get as hot as a class A, yielding to a smaller size and better efficiency (typically 50%).

Class A-B amplifiers are a combination of the two types described above. At lower volumes, the amplifier works in class A. At higher volumes, the amplifier switches to class B operation.

An increasingly popular kind is the class D amplifier (known as digital amplifier). These amplifiers are not really digital (there is no such thing), but operate similarly in the same manner as a digital-to-analog converter. The signal that comes in is sampled a high rates, and then reconstructed at higher power. This type of amplifiers produce almost no heat and are very small in size, but really expensive.  Although there are full-range class D amplifiers available, most high-end manufacturers are designing amps for low frequency applications.  These amps are capable of over 1000 Watts.  Efficiency is much higher in class D amplifiers (~80%).

How To Install An Amplifier!

Remote Turn-on Wire
The remote turn on wire goes to the head unit.  When the radio is on, it puts out 12 volts that turn the amplifier on.  If you are using a factory radio that does not have a remote turn on (or power antenna wire) you can tap into, hook it up to the ignition, so that the amplifier does not remain on when you turn the car off.

If you are using multiple devices (amplifiers, crossovers, equalizers, fans, etc), you might have to add a relay, since typical turn-on wires in a radio can't handle more that 300mA.
  

Power Wiring
Even though amplifiers are easy to install, a lot of things could go wrong. The most important thing to consider is where to get the power from: Straight from the battery.  ALWAYS put a fuse as close to the positive battery terminal as possible. If the wire going to the back of the car shorts out, then the fuse will blow. If you don't install a fuse or breaker and the wire shorts out, then the wire will carry so much current that the insulation will melt and could catch your car on fire. The size of the fuse should be the same rating as the fuses used by the amp(s) or less. The ground (-) should be hooked-up to a metal part of the car. It is not necessary to run a ground wire all the way to the battery.

It is not essential to spend a lot of money in getting 99.999999% copper 0-gage wire and gold connectors unless you are installing a competition system. Here's a table to help decide what gauge wire to use, based on total current draw and length of wire:

RCA Wiring
When running power wires to the amp, keep them as far away from the RCA wires (see alternator noise section for more info), ideally on the other side of the car. It is OK to run the turn-on wire from the radio along with RCA's, since it carries very little current.
  

Mounting
Amplifiers produce a lot of heat and need to receive plenty of fresh air.  If the amplifier is to be mounted under a seat, upside down, in a rack or enclosed, a fan or two might need to be used to increase air flow.

To avoid noise problems, it is good practice to mount the amplifier itself to a piece of wood or other non-conducting material.  That way the only ground it gets is from the ground wire and not the mounting screws.

Amplifier Terms!

RMS Power: The power output of an amplifier should be roughly matched to what the amp will be used for and what speakers it will be driving. Oddly enough, the most common problem with matching speakers and amps is using an amp that is too weak to power the speaker. When an underpowered amp is used to power a speaker, the listener tends to turn the volume up higher in order to get more output of the amplifier. Eventually the amplifier runs into its limit and begins to distort. This distortion can cause the output from the amplifier to become DC for short periods of time and DC signals of even low power can destroy a speaker. Underpowering a speaker in this way can be more dangerous than overpowering it! Also more power is usually necessary when powering subwoofers because of their large size and excursion. Do not plan on using an amp of less than 75watts per channel to drive a subwoofer. The converse holds true for higher frequencies (midrange and treble) only 25-50watts per channel are necessary to drive speakers in those frequency ranges, however more power will not hurt, it just probably will not be used. Another factor in power output is stability in low resistance loads. Sometimes you can wire mutiple subwoofers to a single channel on an amplifier but the amp will have to work harder to drive this kind of load. Many moderately priced amps can drive loads as low as 2 ohms or less, with 4 ohms being the typical load of a single speaker.

Power Supply Regulation: The power supply in an amplifier converts the 12volt DC that is available in your car's electrical system to something the amp can use to produce more power. Several designs are employed by manufacturers today. Two classifications are regulated and unregulated. A regulated supply produces the same power regardless of whether your car's electrical system voltage sags (which a capacitor will help prevent). An amp using a stiffly regulated power supply will be able to supply full power even when the input voltage dips below 12volts. However, it will not gain any power if the input voltage goes above 12volts. An unregulated supply's power output depends directly on the input voltage. This causes changes in the maximum output power with changes in the car's electrical system. I recommend getting an amp with a regulated power supply so power output will be constant regardless of input voltage changes. This changes if you have a stiffening capacitor or another regulation device (Accumatch) to smooth out your car's electrical system. In this case, buy an amp with an unregulated supply. Some cheap amps use unregulated supplies to save money but provide none of the benefits of a typical unregulated supply. One way to determine whether an amp has a regulated supply or not is to view the power output specs for 12volt and 14.4volt inputs. If they are the same then the amp probably has a regulated supply otherwise it has an unregulated one.

Tri-Mode: Some amps can play in what is called "tri-mode." In this mode, 2 channels are used to drive a pair of high frequency speakers and one subwoofer. The subwoofer receives power from both channels. This is a very efficient way to use an amp for more than one purpose. A special crossover is required to separate the two ranges of frequencies and it should have a way of adjusting the output level between the high frequency speakers and the subwoofer. This can be a nice way to save money on your system although it wastes a little bit of amplifier power because of the crossover and it can be more difficult to adjust the relative level between the high and low frequency outputs.

Other Specs: THD (Total Harmonic Distortion) is a spec that often shows up with the power output spec. An example would be "45wattsx2 @ 0.01% THD" This spec says that at an output level of 45watts into each channel the THD will be no more than 0.01%. Sometimes manufacturers will quote the power spec at a THD of 1%. Be wary of this, 1% THD is poor and either implies that the amp is not very high quality or that the manufacturer is artificially inflating the power output spec by running the amp into a higher distortion region where it does produce more power but more distortion as well. Either way it is a sign of a poor amp or marketing that decieves. Anything less than 0.1% is negligible.

Built-in Crossovers: These allow you to use the amp to only amplify certain frequencies and dedicate the amp to a subwoofer or some other specialized speaker. By using an amplifier's built-in crossover you eliminate the need for a separate one which can save you considerable money. There are sophisticated amps on the market today that combine multiple channels and built-in crossovers so that you can use them in place of multiple amps and a separate crossover. They are expensive but often cheaper than buying separate components.

Pre-amp Outputs: Some amps have pre-amp outputs which allow you to "daisy-chain" multiple amps together without splitting the pre-amp output from your head unit. Also, if the amp has a built-in crossover, you can use it to drive another amp. For example if you have an amp you are going to use to drive a subwoofer with a built-in crossover at 90Hz, you can use its built-in crossover to set the amp to only amplify signals below 90Hz for the subwoofer and then have a pre-amp output that only has frequencies above 90Hz which you can connect to an amp that does not have a built-in crossover. That amp can then be used to power the high frequency drivers.

Input Sensitivities: I have received a number of questions about input sensitivities and their importance especially as to why 4 volt outputs on a head unit are better. Here's what an amp does: it takes its input and makes it larger so it can drive speakers. How much larger it can make the input signal is set by the input sensitivity and the maximum power output of the amp. You can turn the input sensitivity all the way up but that does not make the amp put out more power than its max, it just gets to that max level with a smaller input voltage. To see why 4 volt head units are better lets say we have 2 head units, model A puts out a 1 volt signal and model B puts out a 4 volt signal max. We're connecting these head units to a 25 watt amp. The amp puts out 10 volts.

Power = Voltage^2/Resistance = 10^2/4 = 25watts.

To get maximum output from head A, the gain needs to be 10 (10volts out per 1volt in, 10/1 = 10). Now let's say there's 0.1 volt of noise in the signal. With our gain set at 10 with our input sensitivity control we have amplified the noise to 1 volt. Consider what happens with head B. The gain needs to be only 2.5 to get full output. We still get 10 volts of output but the noise is only 0.25 volts. This noise level is 4 times lower than with head A. By using a higher voltage head unit you can set the gain on your amp lower and thus amplify less noise. Also lets say you left the input sensitivity set for a gain of 10 and you used 4 volt head unit at its max. If this did not make the input stage distort it would try to make the amp put out 40 volts (10*4) which would be 400watts! Obviously the amp can't do that and just hits its 25watt limit. To set your input sensitivity, turn you amp's input sensitivity almost all the way down. Now start with your head unit at its lowest volume and turn it up until you hear distortion and then back off some. Some head units will let you go to full volume without distorting the pre-amp level outputs. Now with your head unit putting out its max clean voltage, turn the input sensitivity up until you get to the loudest your system will play without distortion or the loudest you ever care to listen, whichever is lower. Now your amp is set to amplify the least amount necessary to produce full volume making it amplify noise the least.

Amplifier Power Specifications!

This page is intended to explain amplifier power specifications in more detail. I have a BS in Electrical Engineering so I do not know how much of this the average Joe is going to understand. I am also human so there may be mistakes below.  

Amplifier power ratings are important in determining whether an amp will satisfy your system's needs or not. It is necessary for the amp manufacturer to give out a power specification which clear and complete. Otherwise you are just guessing.  An example of a good power amp spec for a 4 channel amp is:

"50watts X 4 RMS all channels driven continuously into 4 ohms with less than 0.1%THD from 20Hz to 20kHz"

Every part of that spec is important and without any part of it the power rating is virutally meaningless. Many times amp manufacturers do not give this much information but you have to judge for yourself whether they are hiding anything. Head unit power ratings are notorious for being very misleading. Now I'll go into what  each part of the spec means and why each is important.

"50watts X 4 RMS all channels driven continuously into 4 ohms with less than 0.1%THD from 20Hz to 20kHz"

The "50watts" part is the one we notice first and everything else qualifies how that "50watts" was measured. Having enough power is what most people look for in an amp. However, other things come into play. If the you are going to run a load less than 4 ohms, then the current capability of the amp is definitely important and most specs do not give a current capability. A power rating into 2 ohms can help though. If the power doubles into 2 ohms then you know that the amp is built strongly enough that it can deliver enough current to drive a 2 ohm load. You may think that this is not important if you are not going to drive 2 ohm loads but it is important. Speakers (woofers, midranges, tweeters, etc) are not purely resistive. They have capacitive and inductive properties as well. Depending on the music and your setup, the impedance may dip well below 4 ohms for a nominally 4 ohm speaker.

Whether you amp can supply current fast enough to reproduce the music faithfully depends partially on the amp's slew rate (how fast its output can change), its damping factor (how easily it can control the speaker) and its current capability. For these reasons 2 ohm power is important even when driving 4 ohm speakers. Slew rates of 100V/microsec and damping factors above 100 (referenced with a 4 ohm load) are good but that information is usually not given out by the amp manufacturer. I hope it is clear now that the number of watts an amp can produce is only one factor in determining whether an amp is capable of the performance you desire.

On a final note on this part of the spec, most head units use IC (integrate circuits or chips) for the built-in amp's output stage. Those chips rarely can provide adequate current which is why even most novices know not drive subwoofers from a head unit. Real amps often have ICs in them as well but the output stages are almost always discrete, meaning they are built from transistors, resistors, capacitors and not integrated together inside tiny ICs.  Advances in IC technology always making them better though.

"50watts X 4 RMS all channels driven continuously into 4 ohms with less than 0.1%THD from 20Hz to 20kHz"

The "X 4" implies that the amp has 4 output channels. The "RMS" stands for "root mean square" and is a method of measuring an AC waveform. More importantly here it implies that the power rating is not just a peak rating but continuous. "all channels driven" means that the power measurement was made with all channels of the amp driven to their maximum level at the same time. This means that the power supply is strong enough to allow all 4 output channels to produce 50watts at the same time.

This is a common place where head unit specs "cheat." They leave off the "all channels driven" and measure only 1 channel at a time which often gives a higher number. I've seen head units claming "30x4" which is meaningless but most people take it to mean that the head unit produces 30watts each into 4 channels. That's 120 watts from a head unit. No amp is 100% efficient so let us say it draws 150 watts to do this (80% efficiency which is still high). With a 12V power input, the head unit amp's power supply would be drawing 12.5 amps. I guarantee you that it is not easy to design a power supply that fits into a head unit leaving enough room for everything else (including the amp stages themselves) for any reasonable price that can deliver that kind of power. That is one reason why I say not preferable to use the head unit's power.

"50watts X 4 RMS all channel driven continuously into 4 ohms with less than 0.1%THD from 20Hz to 20kHz"

"continuously" implies that the measurement was made using a continuous (probably sine wave) test signal and not just a quick burst. An amp capable of producing higher power for short amounts of time will have a higher power rating if they measure power with short bursts instead of a continuous input.

The argument can be made that continuous power is not as important because music by nature is dynamic and therefore the peak power is what we really should concentrate on. My response to this is that there is no standardized burst input which all amp manufacturers would use to measure "peak" power. In the end to make their power ratings look higher they would use extremely short pulses which would not represent the amp's performance with music. Because no standard currently exists for peak power we must rely on continuous power ratings for consistancy and to be able to compare amps with each other.

"50watts X 4 RMS all channel driven continuously into 4 ohms with less than 0.1%THD from 20Hz to 20kHz"

"into 4ohms" means that the power measurement was done using a dummy 4 ohm resistor as the load. This is not the same as a 4 ohm speaker but provides a standard which everyone uses to measure power. Sometimes (but not very often) amp manufacturers will measure power specs into 2 or 3 ohm loads and not say "into 4ohms" only to make the power rating look bigger than it actually is but this is rare. 4 ohms is what car audio amp manufacturers almost always give their power ratings for.

"50watts X 4 RMS all channel driven continuously into 4 ohms with less than 0.1%THD from 20Hz to 20kHz"

"with less than 0.1% THD" tells something about the distortion the amp is producing at this power level. Most amps have an intrinsic distortion that occurs at a near constant level for most of its power range and then when the amp starts to get overdriven the distortion rises quickly. THD stands for "total harmonic distortion" which is one way of measuring distortion that is standardized.

Often a power spec without the THD number was made with the amp driven until the THD reached 1% or more. This gives a higher power rating but you probably would not want to use the amp at that level because it would be distorted. This is a common ploy used when you see a 400watt amp for $50 at a flea market or discount store. This is often another way that head unit amp specs are inflated.  

"50watts X 4 RMS all channel driven continuously into 4 ohms with less than 0.1%THD from 20Hz to 20kHz"

"from 20Hz to 20kHz" tells us the frequency range into which this amp can produce its rated power. Some amps have power curves that fall off at low and high frequencies. Having this part of the spec present gives you reassurance that the amp can produce its power anywhere in the normal audio range. A power spec that says "into 1kHz" or leaves it off could be inflated. Many amps just put the frequency response as a separate datum on the spec sheet and not with the power rating. It should be with the power spec as well. A "+/- 1dB" or something similar should accompany the frequency response so you know how flat the frequency curve is.

That is it for amplifer power specs and be careful with incomplete specs. Even the best manufacturers put out incomplete specs and then it is up to you to figure out whether the amp is well designed or not but it should not be too difficult. You get what you pay for but look at the construction and "feel" of the amp as well to help make your decision. Also, keep in mind that these explanations are valid for home amplification equipment as well, although the FTC has more stringent requirements for power claims of home audio equipment.

Amplifiers
Your amplifier takes the signal from your head unit and makes it large enough to be able to drive your speakers. It is preferable to use separate amps for high and low frequencies but it is not necessary. The problem with using one amp for all frequencies is that you cannot adjust the levels among different frequency ranges as easily as you can adjust outputs of separate amps. Many people start their system with an amplifier for the low frequncies (bass) and use their head units built-in power to drive the higher frequency speakers. This is adequate but the built-in power in a head unit is usually not strong enough for high volume listening and not clean enough for the discerning ear. There are many options when choosing an amplifier.

I've also created a page for understanding power amplifier specifications here.

RMS Power:
The power output of an amplifier should be roughly matched to what the amp will be used for and what speakers it will be driving. Oddly enough, the most common problem with matching speakers and amps is using an amp that is too weak to power the speaker. When an underpowered amp is used to power a speaker, the listener tends to turn the volume up higher in order to get more output of the amplifier. Eventually the amplifier runs into its limit and begins to distort. This distortion can cause the output from the amplifier to become DC for short periods of time and DC signals of even low power can destroy a speaker. Underpowering a speaker in this way can be more dangerous than overpowering it! Also more power is usually necessary when powering subwoofers because of their large size and excursion. Do not plan on using an amp of less than 75watts per channel to drive a subwoofer. The converse holds true for higher frequencies (midrange and treble) only 25-50watts per channel are necessary to drive speakers in those frequency ranges, however more power will not hurt, it just probably will not be used. Another factor in power output is stability in low resistance loads. Sometimes you can wire mutiple subwoofers to a single channel on an amplifier but the amp will have to work harder to drive this kind of load. Many moderately priced amps can drive loads as low as 2 ohms or less, with 4 ohms being the typical load of a single speaker.

Power Supply Regulation:
The power supply in an amplifier converts the 12volt DC that is available in your car's electrical system to something the amp can use to produce more power. Several designs are employed by manufacturers today. Two classifications are regulated and unregulated. A regulated supply produces the same power regardless of whether your car's electrical system voltage sags (which a capacitor will help prevent). An amp using a stiffly regulated power supply will be able to supply full power even when the input voltage dips below 12volts. However, it will not gain any power if the input voltage goes above 12volts. An unregulated supply's power output depends directly on the input voltage. This causes changes in the maximum output power with changes in the car's electrical system. I recommend getting an amp with a regulated power supply so power output will be constant regardless of input voltage changes. This changes if you have a stiffening capacitor or another regulation device (Accumatch) to smooth out your car's electrical system. In this case, buy an amp with an unregulated supply. Some cheap amps use unregulated supplies to save money but provide none of the benefits of a typical unregulated supply. One way to determine whether an amp has a regulated supply or not is to view the power output specs for 12volt and 14.4volt inputs. If they are the same then the amp probably has a regulated supply otherwise it has an unregulated one.

Tri-Mode:
Some amps can play in what is called "tri-mode." In this mode, 2 channels are used to drive a pair of high frequency speakers and one subwoofer. The subwoofer receives power from both channels. This is a very efficient way to use an amp for more than one purpose. A special crossover is required to separate the two ranges of frequencies and it should have a way of adjusting the output level between the high frequency speakers and the subwoofer. This can be a nice way to save money on your system although it wastes a little bit of amplifier power because of the crossover and it can be more difficult to adjust the relative level between the high and low frequency outputs.

Other Specs:
THD (Total Harmonic Distortion) is a spec that often shows up with the power output spec. An example would be "45wattsx2 @ 0.01% THD" This spec says that at an output level of 45watts into each channel the THD will be no more than 0.01%. Sometimes manufacturers will quote the power spec at a THD of 1%. Be wary of this, 1% THD is poor and either implies that the amp is not very high quality or that the manufacturer is artificially inflating the power output spec by running the amp into a higher distortion region where it does produce more power but more distortion as well. Either way it is a sign of a poor amp or marketing that decieves. Anything less than 0.1% is negligible.

Built-in Crossovers:
These allow you to use the amp to only amplify certain frequencies and dedicate the amp to a subwoofer or some other specialized speaker. By using an amplifier's built-in crossover you eliminate the need for a separate one which can save you considerable money. There are sophisticated amps on the market today that combine multiple channels and built-in crossovers so that you can use them in place of multiple amps and a separate crossover. They are expensive but often cheaper than buying separate components.

Pre-amp Outputs:
Some amps have pre-amp outputs which allow you to "daisy-chain" multiple amps together without splitting the pre-amp output from your head unit. Also, if the amp has a built-in crossover, you can use it to drive another amp. For example if you have an amp you are going to use to drive a subwoofer with a built-in crossover at 90Hz, you can use its built-in crossover to set the amp to only amplify signals below 90Hz for the subwoofer and then have a pre-amp output that only has frequencies above 90Hz which you can connect to an amp that does not have a built-in crossover. That amp can then be used to power the high frequency drivers.

Input Sensitivities:
I have received a number of questions about input sensitivities and their importance especially as to why 4 volt outputs on a head unit are better. Here's what an amp does: it takes its input and makes it larger so it can drive speakers. How much larger it can make the input signal is set by the input sensitivity and the maximum power output of the amp. You can turn the input sensitivity all the way up but that does not make the amp put out more power than its max, it just gets to that max level with a smaller input voltage. To see why 4 volt head units are better lets say we have 2 head units, model A puts out a 1 volt signal and model B puts out a 4 volt signal max. We're connecting these head units to a 25 watt amp. The amp puts out 10 volts.

Power = Voltage^2/Resistance = 10^2/4 = 25watts.
To get maximum output from head A, the gain needs to be 10 (10volts out per 1volt in, 10/1 = 10). Now let's say there's 0.1 volt of noise in the signal. With our gain set at 10 with our input sensitivity control we have amplified the noise to 1 volt. Consider what happens with head B. The gain needs to be only 2.5 to get full output. We still get 10 volts of output but the noise is only 0.25 volts. This noise level is 4 times lower than with head A. By using a higher voltage head unit you can set the gain on your amp lower and thus amplify less noise. Also lets say you left the input sensitivity set for a gain of 10 and you used 4 volt head unit at its max. If this did not make the input stage distort it would try to make the amp put out 40 volts (10*4) which would be 400watts! Obviously the amp can't do that and just hits its 25watt limit. To set your input sensitivity, turn you amp's input sensitivity almost all the way down. Now start with your head unit at its lowest volume and turn it up until you hear distortion and then back off some. Some head units will let you go to full volume without distorting the pre-amp level outputs. Now with your head unit putting out its max clean voltage, turn the input sensitivity up until you get to the loudest your system will play without distortion or the loudest you ever care to listen, whichever is lower. Now your amp is set to amplify the least amount necessary to produce full volume making it amplify noise the least.  
Amplifier Power Ratings
Amplifier power ratings are important in determining whether an amp will satisfy your system's needs or not. It is necessary for the amp manufacturer to give out a power specification which clear and complete. Otherwise you are just guessing.  An example of a good power amp spec for a 4 channel amp is:

"50watts X 4 RMS all channels driven continuously into 4 ohms
with less than 0.1%THD from 20Hz to 20kHz"

Every part of that spec is important and without any part of it the power rating is virutally meaningless. Many times amp manufacturers do not give this much information but you have to judge for yourself whether they are hiding anything. Head unit power ratings are notorious for being very misleading. Now I'll go into what each part of the spec means and why each is important.

The "50watts" part is the one we notice first and everything else qualifies how that "50watts" was measured. Having enough power is what most people look for in an amp. However, other things come into play. If the you are going to run a load less than 4 ohms, then the current capability of the amp is definitely important and most specs do not give a current capability. A power rating into 2 ohms can help though. If the power doubles into 2 ohms then you know that the amp is built strongly enough that it can deliver enough current to drive a 2 ohm load. You may think that this is not important if you are not going to drive 2 ohm loads but it is important. Speakers (woofers, midranges, tweeters, etc) are not purely resistive. They have capacitive and inductive properties as well. Depending on the music and your setup, the impedance may dip well below 4 ohms for a nominally 4 ohm speaker.

Whether you amp can supply current fast enough to reproduce the music faithfully depends partially on the amp's slew rate (how fast its output can change), its damping factor (how easily it can control the speaker) and its current capability. For these reasons 2 ohm power is important even when driving 4 ohm speakers. Slew rates of 100V/microsec and damping factors above 100 (referenced with a 4 ohm load) are good but that information is usually not given out by the amp manufacturer. I hope it is clear now that the number of watts an amp can produce is only one factor in determining whether an amp is capable of the performance you desire.

On a final note on this part of the spec, most head units use IC (integrate circuits or chips) for the built-in amp's output stage. Those chips rarely can provide adequate current which is why even most novices know not drive subwoofers from a head unit. Real amps often have ICs in them as well but the output stages are almost always discrete, meaning they are built from transistors, resistors, capacitors and not integrated together inside tiny ICs.  Advances in IC technology always making them better though.

The "X 4" implies that the amp has 4 output channels. The "RMS" stands for "root mean square" and is a method of measuring an AC waveform. More importantly here it implies that the power rating is not just a peak rating but continuous. "all channels driven" means that the power measurement was made with all channels of the amp driven to their maximum level at the same time. This means that the power supply is strong enough to allow all 4 output channels to produce 50watts at the same time.

This is a common place where head unit specs "cheat." They leave off the "all channels driven" and measure only 1 channel at a time which often gives a higher number. I've seen head units claming "30x4" which is meaningless but most people take it to mean that the head unit produces 30watts each into 4 channels. That's 120 watts from a head unit. No amp is 100% efficient so let us say it draws 150 watts to do this (80% efficiency which is still high). With a 12V power input, the head unit amp's power supply would be drawing 12.5 amps. I guarantee you that it is not easy to design a power supply that fits into a head unit leaving enough room for everything else (including the amp stages themselves) for any reasonable price that can deliver that kind of power. That is one reason why I say not preferable to use the head unit's power.

"continuously" implies that the measurement was made using a continuous (probably sine wave) test signal and not just a quick burst. An amp capable of producing higher power for short amounts of time will have a higher power rating if they measure power with short bursts instead of a continuous input.

The argument can be made that continuous power is not as important because music by nature is dynamic and therefore the peak power is what we really should concentrate on. My response to this is that there is no standardized burst input which all amp manufacturers would use to measure "peak" power. In the end to make their power ratings look higher they would use extremely short pulses which would not represent the amp's performance with music. Because no standard currently exists for peak power we must rely on continuous power ratings for consistancy and to be able to compare amps with each other.

"into 4ohms" means that the power measurement was done using a dummy 4 ohm resistor as the load. This is not the same as a 4 ohm speaker but provides a standard which everyone uses to measure power. Sometimes (but not very often) amp manufacturers will measure power specs into 2 or 3 ohm loads and not say "into 4ohms" only to make the power rating look bigger than it actually is but this is rare. 4 ohms is what car audio amp manufacturers almost always give their power ratings for.

"with less than 0.1% THD" tells something about the distortion the amp is producing at this power level. Most amps have an intrinsic distortion that occurs at a near constant level for most of its power range and then when the amp starts to get overdriven the distortion rises quickly. THD stands for "total harmonic distortion" which is one way of measuring distortion that is standardized.

Often a power spec without the THD number was made with the amp driven until the THD reached 1% or more. This gives a higher power rating but you probably would not want to use the amp at that level because it would be distorted. This is a common ploy used when you see a 400watt amp for $50 at a flea market or discount store. This is often another way that head unit amp specs are inflated.

"from 20Hz to 20kHz" tells us the frequency range into which this amp can produce its rated power. Some amps have power curves that fall off at low and high frequencies. Having this part of the spec present gives you reassurance that the amp can produce its power anywhere in the normal audio range. A power spec that says "into 1kHz" or leaves it off could be inflated. Many amps just put the frequency response as a separate datum on the spec sheet and not with the power rating. It should be with the power spec as well. A "+/- 1dB" or something similar should accompany the frequency response so you know how flat the frequency curve is.

That is it for amplifer power specs and be careful with incomplete specs. Even the best manufacturers put out incomplete specs and then it is up to you to figure out whether the amp is well designed or not but it should not be too difficult. You get what you pay for but look at the construction and "feel" of the amp as well to help make your decision. Also, keep in mind that these explanations are valid for home amplification equipment as well, although the FTC has more stringent requirements for power claims of home audio equipment.  
Understanding Ohm's Law
Understanding what ohms are and how they relate to car audio is most helpful when trying to determine optimal wiring configurations for connecting multiple speakers to an amp. There are some basic electrical engineering formulas I will use on this page. Fortunately they are fairly simple.

Ohm's law: Current = Voltage / Resistance or I = V / R
You can rearrange this formula in a couple ways: V = I * R and R = V / I

Power equation: Power = Voltage^2 / Resistance or P = V^2 / R
Rearranging this formula gives us: R = V^2 / P and V = SQRT(P * R)

Using Ohm's law we can derive some more power equations: P = I^2 * R
Rearranging gives us: I = SQRT(P / R)

Abbreviations used on this page are:
I : current, measured in amps
V: voltage, measured in volts
R: resistance, measured in ohms
P: power, measured in watts

With that out of the way we can get down to business. As stated earlier, ohms are a measure of electrical resistance. It helps in this discussion if we consider amplifiers to be perfect voltage sources.

Consider this 25 watt amp:

P = V^2 / R

Most amps are rated into 4 ohm loads so we now have:

25 watts = V^2 / 4 ohms

Solving for voltage we get: V = SQRT(25 * 4) = 10 volts

So our 25 watt amp can be considered here to have the ability to produce up to 10 volts output.

Now let us consider what happens when we connect two speakers in parallel to the amp. At this point I am going to introduce some more formulas. We are considering speakers to just be simple 4 ohm resistors for this discussion. There are formulas which dictate what happens when you combine resistors in various ways. Before that we need to explain what is meant by parallel and series ConneXions.

Each channel of an amplifier has a positive (+) and negative (-) connection. The amp develops a voltage between these two terminals and this voltage is what drives the speakers. The equivalent resistance of what you connect to the amp is referred to as the load.

Normally when connecting a single speaker to a single amp channel you merely connect the "+" terminal of the speaker to the "+" terminal of the amp. Then do the same thing for the "-" terminals. Things get more complicated when you are connecting multiple speakers to a single amp channel. In a parallel configuration you connect both "+" terminals of the speakers to the "+" terminal of the amp. Then do the same thing for the "-" terminals.

A series connection is a little more complicated. First, you connect the "+" terminal of the amp to the "+" terminal of one of the speakers (let us call it speaker A). The next thing you do is connect the "-" terminal of speaker A to the "+" terminal of the other speaker (speaker B). Lastly, you connect the "-" terminal of speaker B to the "-" terminal of the amp. You can see in this connection that power from the amp goes through both speakers one after the other, hence the name "series."

Finally, here are the formulas that tell you what resistance load you end up with when wiring multiple speakers:

For two speakers in parallel:

1 / Rt = 1 / Ra  +  1 / Rb

where Rt is the total equivalent resistance or load and Ra and Rb are the resistances of the two speakers. You can see that you can use speakers of different resistances but there other implications of doing that which are usually undesirable because the power will not be spread evenly between the speakers.

Working through the math if you put two 4 ohm speakers in parallel you get:

1 / Rt = 1 / 4  +  1 / 4  =  1 / 2,  Rt = 2 ohms

The equivalent resistance is exactly half of what we started with. We will look at the implications of this a little later. Let us do another example first with three 4 ohm speakers in parallel:

1 / Rt = 1 / 4  + 1 / 4  +  1 / 4  =  3 / 4, Rt = 4 /3 = 1.33 ohms

You can see that as you put more and more speakers in parallel the equivalent resistance will drop further.

Next lets look at the equivalent resistance for speakers in series:

Rt = Ra + Rb

Now that is easy! You just add the resistances for each speaker so putting two 4 ohm speakers in series will you give a single load of 8 ohms.

With that background out of the way we can look at what effect these different wiring combinations have on the amplifier. Going back our 25 watt (10 volt) amplifier with a single 4 ohm speaker we have:

Current = Voltage / Resistance = 10 / 4 = 2.5 amps

So when this amp is producing maximum power (25 watts) into a 4 ohm load, the load will draw 2.5 amps from the amp.

Now let us look at what happens when we connect two 4 ohm speakers in parallel (which gives us a 2 ohm equivalent load) to this amp:

Power = Voltage^2 / Resistance = 10^2 / 2 = 50 watts

This is seems great! Our 25 watt amp is now producing 50 watts but there are some complications. Let us see the current now:

Current = Voltage / Resistance = 10 / 2 = 5 amps

Even though our voltage is still the same (10 volts) our current has now doubled from 2.5 amps to 5 amps.  If the amp has the capability to produce this much current and dissipate the heat that this will generate then everything will be fine.  One way to determine if your amp is capable of this is to look for power ratings that are given into 2 ohms in addition to the normal 4 ohm rating.  Further if the power doubles into the 2 ohm rating then the amp has ample current capacity.  Another clue to tell whether the amp will work with 2 ohm loads is look for the phrase "2 ohm stable."  Being 2 ohm stable only means that the amp will function with 2 ohm loads; it does not necessarily mean that the amp will produce more power into 2 ohms.  If you attempt to use a 2 ohm load with an amp that cannot handle it a well designed amp will shut itself off or blow a fuse and a poor one could be permanently damaged.

Next let us look at a series connection with two 4 ohm speakers. This will give us an 8 ohm load and we will use our 25 watt (10 volt) amplifier again:

P = V^2 / R = 10^2 / 8 = 12.5 watts

Our amp is now producing only half its power rating! And the current is:

I = V / R = 10 / 8 = 1.25 amps

The current is 1/2 its original value as well. Series ConneXions are not used as often as parallel ConneXions because they reduce power. However, they are easier for your amp to drive since they draw less current.

Another option that is often available is to bridge an amplifier. This process takes 2 amp channels and combines them to act as a single more powerful amp channel. How to do this to an amp and wire everything varies so please do not ask me how to bridge your amp. I can explain the effects of it though.

What typically happens when you bridge an amp is that the voltage it can produce doubles. Our 25 watt (10 volt) amp can now produce 20 volts. Let us look at how that affects power:

P = V^2 / R = 20^2 / 4 = 100 watts

This is 4 times the original power of the amp but let us look at the current situation:

I = V / R = 20 / 4 = 5 amps

So now we see even with a regular 4 ohm load the current is already double what the normal value (2.5 amps) was. For other reasons the power usually does not usually quadruple when you bridge an amp but will typically at least double. Connecting a 2 ohm load to a bridged amp raises the current requirement even more. However, if your amp can handle it then you will be squeezing a lot of power out of the amp.

In fact, many people use that kind of setup in competition where the classes are judged by the power rating of the amps in the system. A 25 watt amp can produce many times more power when bridged and driving low resistance loads so the competitor gets more power than what appears on the surface. Zapco and Phoenix Gold make amps which are able to drive such low resistance loads (sometimes as low as 0.5 ohm!)

Some final notes:

• On this page I have considered amplifiers to be perfect voltage sources. They are not though and they have some internal resistance which lowers power output slightly.
• I have also considered speakers to be perfect 4 ohm resistors. In actuality the resistance of the speaker depends on the frequency the speaker is playing. For example, a speaker may have a 3 ohm resistance at 80 Hz and a 9 ohm resistance at 300 Hz. If you were to make a plot of resistance versus frequency you would get what is called the impedance curve of the speaker. Also, speakers act in some ways as inductors and capacitors so a true model of a speaker must include those components as well. How does this affect the sound you ask? Well if you have an amp that has very weak current capability it may work fine into perfect 4 ohm loads but when you connect our real speaker which has an impedance dip at 80 Hz the amp may have difficulty and smear sounds that have 80 Hz components. These are minor but audible effects. This is why it is good to get a 2 ohm stable amp even if you never plan on running 2 ohm loads.
• Placing speakers in parallel and bridging amp channels are effective methods for increasing the power in your system assuming your amp can handle the increased demand.
• Use a series configuration when you need to raise the effective resistance of the load. This occurs more often when you are using dual voice coil speakers.
• Dual voice speakers have two speaker ConneXions on them. This typically increases power handling capability and gives you more wiring options. For example, if you have two dual 4 ohm voice coil speakers you can get a single 4 ohm load which is suitable for connecting to a bridged amp. You would do this by connecting the voice coils on each speaker to each other in series. This would give you two 8 ohm speakers. Next you put those two 8 ohm speakers in parallel and this will give you a single 4 ohm equivalent load.
• Be aware that using lower resistance loads and bridging produces a greater load on the amp. Well designed amps that cannot handle the demand will either shut themselves off or blow a fuse. A poorer designed amp can permanently damage itself. Also, even if an amp works in these configurations it will probably generate more heat so ventilation is even more important.
• As mentioned earlier ohms are a measure of electrical resistance. You should be able to understand why resistance changes affect the amp power as it does. If you raise the resistance the amp is not able to drive as much current through the load and thus you get less power. If you lower the resistance of the load math says that more current will be drawn from the amp. Assuming the amp can handle this you get more power.
• To understand why series and parallel configurations have the effect on resistance that they do consider this. When you connect speakers in series current must flow through both speakers and so it hits the resistance of both speakers. When you have speakers in parallel, the current has multiple paths since it can go through either speaker so the equivalent resistance is always lower than that of either speaker alone.

 

Ohm's Law

Voltage (volts) is the force that moves electrons, forcing a current.  Voltage can be compared to a tank of water elevated at a certain height (potential).   If the tank is placed low (low voltage), water will not flow very quickly (low current).  If the tank is raised to a higher location (higher voltage), the water will flow rapidly (high current).

Current (Amperes) is, in simple terms a measurement of how many electrons flow through a device.  In the water tank analogy, current would be water flow rate.

Resistance (Ohms) slows down current flow.  The higher the resistance of a circuit, the lower the current will be.  Resistance would be equivalent to pipe size.   If you have the water tank at a high level, but the pipe is very small in diameter (high resistance), not much water will flow.  If you use a big pipe (low resistance), then the water flow rate will be larger.

Knowing the relationships between voltage, current and resistance brings us to ohm's law:  "Current is proportional to Voltage divided by Resistance".  This equation can be manipulated to obtain any value knowing the other two.  For example, by measuring the voltage and current of a circuit, resistance can be calculated by dividing voltage by current.  When a circuit is open (disconnected), the resistance is infinite (zero current).  The formula also shows what happens when a circuit is shorted (resistance = 0): The battery will put out as much current as it can instantaneously (not a good sight).

DC vs. AC Circuits

On a DC circuit, current flows in one direction only.   Voltage can remain at a level or change, but it always has the same polarity.   A car's battery produces DC voltage.

AC circuits are a bit more complicated to understand.  The voltage supply reverses its polarity switching from positive to negative.  The current produced goes in one direction while the voltage is positive and then flows in the opposite direction when voltage is reversed.  AC circuits have a frequency associated with them.  The frequency (Hertz or Hz) is how many times per second (cycles) the current (and voltage) switch from positive to negative and back.  The higher the frequency, the faster the circuit will switch polarity.  AC voltage in the car is produced by the alternator, which is converted to DC voltage to charge the battery (even though some of the AC energy from the alternator remains in the electrical system, this is what causes alternator whine when the car is running).  The audio signal that comes from the head unit, gets amplified and drives the speakers is also an AC signal.

A Typical DC Circuit

Electrons flow in a circuit from the negative side of the battery to the positive side of the battery (that is why physicists will argue with the direction of the current in the circuit).  Engineers represent current in the opposite direction of electron flow, as in the diagram.  It does not matter what convention you follow for current direction.  The important thing to keep in mind is how much current flows through the circuit, and that you stick to only one of the models when analyzing a circuit.
For a circuit to have current, there has to be a path (i. e. wire) and a battery.  A circuit also has a resistance, which slows down flow of electrons.
If the path is broken, current can not flow.  The battery supplies the voltage.  The top portion of the circuit in a car is represented by the positive battery cable going to the fuse box and to all the accessories (radio, wipers, lights, etc).  Each accessory has a resistance.  As more accessories are added, the resistance drops, and more current flows through the circuit.  To save money, car manufacturers use the car metal for the bottom part of the circuit, instead of running a ground wire to every device.

Common Engineering Notations

To represent very high or low values, zeros or decimal points are represented by letters.  These are the most common used in car audio:

Symbol:	Value:	Used mainly For:	Example:
µ (micro)	millionth	Capacitors, which are measured in Farads	0.000001F = 1µF
m (mili)	thousandth	Capacitors (F), inductors (Henries), voltage (V), current (A)	0.001Volts = 1mV
k (kilo)	thousand	Resistance (Ohms), frequency (Hertz), power (Watts)	1000W = 1kW
M (mega)	million	Frequency (Hz), resistance(Ohms)	1,000,000 Hz = 1MHz

 

Voltage Calculations

This portion of this site is intended to help you calculate voltage levels. You can calculate any unknown value if you know the other two in the equation.

Explanation of Terms

E - stands for voltage, the unit is the Volt.

I - stands for current, the unit is the Amp.

P - stands for power, the unit is the Watt.

R - stands for resistance/impedance, the unit is the Ohm.

The Formulas

E = I x R E = P / I E =

Voltage

Click the unknown measurement type (Current/Power/Resistance), then enter the two values that you do know, and press the "Calculate Power" button to get your answer. If you have more than one value to calculate, just change the value(s) you want to adjust and click the button again (if you change to a new measurement type - make sure you click the reset button).

Which number is unknown ? Current  Power  Resistance

Enter Current Amps Enter Power Watts Enter Resistance  Ohms

Voltage =  Volts

 

About Relays?

Operation
Relays do exactly the same thing a regular switch.   Instead of being moved by a finger, they are moved by an electromagnet that attracts a metal switch.  When the "switch" is inactive (no power through electromagnet) the common and normally closed contacts are tied together.

  

When the relay is activated (12 volts across electromagnet), the switch is pulled, disconnecting normally closed contact, and connecting the normally open contact with common terminal.  As soon a power is removed from the coil, the contacts go back to their original position.

Do you need a relay?

Most head units have an output to turn on amplifiers, etc.  These outputs are designed to turn on a small number of devices, so they provide very little current.

On high-end systems, when many devices (amplifiers, crossovers, equalizers, processors, fans, etc) have to be connected to this turn-on wire the current output might not be enough.  If the circuit is overloaded, it can blow a fuse or even damage the head unit.

There is an easy way around this problem:  Add a relay.

How many devices are too many?  Depends on how much current each device draws and how much current the head unit provides.  Check the specifications section of the manuals to see.  Typically, pieces of equipment such as amplifiers, crossovers and equalizers draw very little current, since their turn-on switches are either solid state or small relays.  If you are hooking other devices that draw more current such as neon lights, fans, actuators, motors, etc, then you definitely need to add a relay.  An easy way to tell how much current devices are drawing is to check with a current meter.
  

Connections

The diagram to the left shows the connections required to get the turn-on output.  The relay can be located either behind the radio, trunk, or elsewhere in the car.  Usually, it is easier behind the radio because wires going to the relay are shorter.

Terminal 87 goes to constant power (+12v).  It can be obtained from the same wire where the radio's memory backup is connected.

Terminal 86 goes to ground (negative wire going to the head unit or to a metal part that is connected to the chassis of the vehicle).

Terminal 85 is connected to the remote turn-on wire output at the head unit. Lastly, terminal 30 is run to all the components that need to be turned on.

 

About Diodes?

There are different types of diodes for different applications.   For vehicles, we are mostly interested in rectifier diodes.  Rectifier diodes, in simple terms, are "valves" that allow current to flow in one direction only.

Uses
Different circuits can be isolated to avoid undesired interactions.   Diodes are also used to protect circuits.  In car applications, diodes are used to isolate switches and sensors in security systems.  Diodes can also eliminate current transients in inductive components such as relays.

Purchasing the Correct Diode

The top image on the left is the symbol commonly used in circuit diagrams to represent diodes.
Most rectifier diodes are small black tubes with a white line at one end and look like the bottom image on the left.  The white line is commonly called the "negative" side (or cathode).  The other end of a diode is called the anode.

Diodes can be obtained at any electronic parts store such as Radio Shack.  Low current diodes (1 amp or less) are very cheap.  Several diodes can be purchased for a dollar.  Higher current diodes do cost more.

Current Ratings
For circuit isolation purposes (i.e. isolating switches or alarm sensors), 1 amp diodes would suffice. Other applications, such as isolating parking lights circuits in cars require diodes that can handle more current, say 3 amps.

By hooking up diodes in parallel, larger current capabilities can be obtained. For example, by connecting two 1 amp diodes in parallel, a total of 2 amps can be passed through the diodes.

Modes of Operation

	If you want a diode to conduct current, hook it up in the "forward bias" mode. In the forward bias mode, the diode will behave as a short circuit (i.e. being replaced by a wire).
	If the purpose of a diode in a circuit is to block current, then try the "reversed bias" operation. In the reverse bias mode, it can be represented by an open circuit (i.e., cutting the wire in the circuit).

Voltage Considerations
Diodes do have shortcomings. A typical diode has a voltage drop of 0.7 volts. This is not critical for most car applications, but should be taken into consideration for other applications.

Exceeding voltage limits of diodes is not a concern in car applications because we deal with only 12 volts. For higher voltage circuits, the diode's maximum voltage ratings on forward and reverse bias should be observed.

 

ohms?

This page is intended to help people understand "ohms" in more detail. It also addresses parallel / series wiring configurations along with bridging amplifiers.  Dual voice speakers are mentioned in the notes as well.  I have a BS in Electrical Engineering so I do not know how much of this the average Joe is going to understand. I am also human so there may be mistakes below.

Understanding what ohms are and how they relate to car audio is most helpful when trying to determine optimal wiring configurations for connecting multiple speakers to an amp.  There are some basic electrical engineering formulas I will use on this page.  Fortunately they are fairly simple.  Here they are:

Ohm's law: Current = Voltage / Resistance   or    I = V / R
You can rearrange this formula in a couple ways:   V = I * R    and    R = V / I

Power equation:  Power = Voltage^2 / Resistance    or    P = V^2 / R
Rearranging this formula gives us:   R = V^2 / P    and    V = SQRT(P * R)
Using Ohm's law we can derive some more power equations:  P = I^2 * R
Rearranging gives us:    I = SQRT(P / R)

Abbreviations used on this page are:
I : current, measured in amps
V: voltage, measured in volts
R: resistance, measured in ohms
P: power, measured in watts

With that out of the way we can get down to business.  As stated earlier, ohms are a measure of electrical resistance.  It helps in this discussion if we consider amplifiers to be perfect voltage sources.  Consider this 25 watt amp:

P = V^2 / R

Most amps are rated into 4 ohm loads so we now have:

25 watts = V^2 / 4 ohms

Solving for voltage we get:  V = SQRT(25 * 4) = 10 volts

So our 25 watt amp can be considered here to have the ability to produce up to 10 volts output.

Now let us consider what happens when we connect two speakers in parallel to the amp.  At this point I am going to introduce some more formulas.  We are considering speakers to just be simple 4 ohm resistors for this discussion.  There are formulas which dictate what happens when you combine resistors in various ways.  Before that we need to explain what is meant by parallel and series connections.

Each channel of an amplifier has a positive (+) and negative (-) connection.  The amp develops a voltage between these two terminals and this voltage is what drives the speakers.  The equivalent resistance of what you connect to the amp is referred to as the load.

Normally when connecting a single speaker to a single amp channel you merely connect the "+" terminal of the speaker to the "+" terminal of the amp.  Then do the same thing for the "-" terminals.  Things get more complicated when you are connecting multiple speakers to a single amp channel.  In a parallel configuration you connect both "+" terminals of the speakers to the "+" terminal of the amp.  Then do the same thing for the "-" terminals.

A series connection is a little more complicated.  First, you connect the "+" terminal of the amp to the "+" terminal of one of the speakers (let us call it speaker A).  The next thing you do is connect the "-" terminal of speaker A to the "+" terminal of the other speaker (speaker B).  Lastly, you connect the "-" terminal of speaker B to the "-" terminal of the amp.  You can see in this connection that power from the amp goes through both speakers one after the other, hence the name "series."

Finally, here are the formulas that tell you what resistance load you end up with when wiring multiple speakers:

For two speakers in parallel:

1 / Rt = 1 / Ra  +  1 / Rb

where Rt is the total equivalent resistance or load and Ra and Rb are the resistances of the two speakers.  You can see that you can use speakers of different resistances but there other implications of doing that which are usually undesirable because the power will not be spread evenly between the speakers.

Working through the math if you put two 4 ohm speakers in parallel you get:

1 / Rt = 1 / 4  +  1 / 4  =  1 / 2,  Rt = 2 ohms

The equivalent resistance is exactly half of what we started with.  We will look at the implications of this a little later.  Let us do another example first with three 4 ohm speakers in parallel:

1 / Rt = 1 / 4  + 1 / 4  +  1 / 4  =  3 / 4, Rt = 4 /3 = 1.33 ohms

You can see that as you put more and more speakers in parallel the equivalent resistance will drop further.

Next lets look at the equivalent resistance for speakers in series:

Rt = Ra + Rb

Now that is easy!  You just add the resistances for each speaker so putting two 4 ohm speakers in series will you give a single load of 8 ohms.

With that background out of the way we can look at what effect these different wiring combinations have on the amplifier.  Going back our 25 watt (10 volt) amplifier with a single 4 ohm speaker we have:

Current = Voltage / Resistance = 10 / 4 = 2.5 amps

So when this amp is producing maximum power (25 watts) into a 4 ohm load, the load will draw 2.5 amps from the amp.

Now let us look at what happens when we connect two 4 ohm speakers in parallel (which gives us a 2 ohm equivalent load) to this amp:

Power = Voltage^2 / Resistance = 10^2 / 2 = 50 watts

This is seems great!  Our 25 watt amp is now producing 50 watts but there are some complications.  Let us see the current now:

Current = Voltage / Resistance = 10 / 2 = 5 amps

Even though our voltage is still the same (10 volts) our current has now doubled from 2.5 amps to 5 amps.  If the amp has the capability to produce this much current and dissipate the heat that this will generate then everything will be fine.  One way to determine if your amp is capable of this is to look for power ratings that are given into 2 ohms in addition to the normal 4 ohm rating.  Further if the power doubles into the 2 ohm rating then the amp has ample current capacity.  Another clue to tell whether the amp will work with 2 ohm loads is look for the phrase "2 ohm stable."  Being 2 ohm stable only means that the amp will function with 2 ohm loads; it does not necessarily mean that the amp will produce more power into 2 ohms.  If you attempt to use a 2 ohm load with an amp that cannot handle it a well designed amp will shut itself off or blow a fuse and a poor one could be permanently damaged.

Next let us look at a series connection with two 4 ohm speakers.  This will give us an 8 ohm load and we will use our 25 watt (10 volt) amplifier again:

P = V^2 / R = 10^2 / 8 = 12.5 watts

Our amp is now producing only half its power rating!  And the current is:

I = V / R = 10 / 8 = 1.25 amps

The current is 1/2 its original value as well.  Series connections are not used as often as parallel connections because they reduce power.  However, they are easier for your amp to drive since they draw less current.

Another option that is often available is to bridge an amplifier.  This process takes 2 amp channels and combines them to act as a single more powerful amp channel.  How to do this to an amp and wire everything varies so please do not ask me how to bridge your amp.  I can explain the effects of it though.

What typically happens when you bridge an amp is that the voltage it can produce doubles.  Our 25 watt (10 volt) amp can now produce 20 volts.  Let us look at how that affects power:

P = V^2 / R = 20^2 / 4 = 100 watts

This is 4 times the original power of the amp but let us look at the current situation:

I = V / R = 20 / 4 = 5 amps

So now we see even with a regular 4 ohm load the current is already double what the normal value (2.5 amps) was.  For other reasons the power usually does not usually quadruple when you bridge an amp but will typically at least double.  Connecting a 2 ohm load to a bridged amp raises the current requirement even more.  However, if your amp can handle it then you will be squeezing a lot of power out of the amp.

In fact, many people use that kind of setup in competition where the classes are judged by the power rating of the amps in the system.  A 25 watt amp can produce many times more power when bridged and driving low resistance loads so the competitor gets more power than what appears on the surface.  Zapco and Phoenix Gold make amps which are able to drive such low resistance loads (sometimes as low as 0.5 ohm!)

Some final notes:

• On this page I have considered amplifiers to be perfect voltage sources.  They are not though and they have some internal resistance which lowers power output slightly.

• I have also considered speakers to be perfect 4 ohm resistors.  In actuality the resistance of the speaker depends on the frequency the speaker is playing.  For example, a speaker may have a 3 ohm resistance at 80 Hz and a 9 ohm resistance at 300 Hz.  If you were to make a plot of resistance versus frequency you would get what is called the impedance curve of the speaker.  Also, speakers act in some ways as inductors and capacitors so a true model of a speaker must include those components as well.  How does this affect the sound you ask?  Well if you have an amp that has very weak current capability it may work fine into perfect 4 ohm loads but when you connect our real speaker which has an impedance dip at 80 Hz the amp may have difficulty and smear sounds that have 80 Hz components.  These are minor but audible effects.  This is why it is good to get a 2 ohm stable amp even if you never plan on running 2 ohm loads.

• Placing speakers in parallel and bridging amp channels are effective methods for increasing the power in your system assuming your amp can handle the increased demand.

• Use a series configuration when you need to raise the effective resistance of the load.  This occurs more often when you are using dual voice coil speakers.

• Dual voice speakers have two speaker connections on them.  This typically increases power handling capability and gives you more wiring options.  For example, if you have two dual 4 ohm voice coil speakers you can get a single 4 ohm load which is suitable for connecting to a bridged amp.  You would do this by connecting the voice coils on each speaker to each other in series.  This would give you two 8 ohm speakers.  Next you put those two 8 ohm speakers in parallel and this will give you a single 4 ohm equivalent load.

• Be aware that using lower resistance loads and bridging produces a greater load on the amp.  Well designed amps that cannot handle the demand will either shut themselves off or blow a fuse.  A poorer designed amp can permanently damage itself.  Also, even if an amp works in these configurations it will probably generate more heat so ventilation is even more important.

• As mentioned earlier ohms are a measure of electrical resistance.  You should be able to understand why  resistance changes affect the amp power as it does.  If you raise the resistance the amp is not able to drive as much current through the load and thus you get less power.  If you lower the resistance of the load math says that more current will be drawn from the amp.  Assuming the amp can handle this you get more power.

• To understand why series and parallel configurations have the effect on resistance that they do consider this.  When you connect speakers in series current must flow through both speakers and so it hits the resistance of both speakers.  When you have speakers in parallel, the current has multiple paths since it can go through either speaker so the equivalent resistance is always lower than that of either speaker alone.

Electrical Current Calculations

This portion of this site is intended to help you calculate current levels in a circuit. You can calculate any unknown value if you know the other two in the equation.

Explanation of Terms

E - stands for voltage, the unit is the Volt.

I - stands for current, the unit is the Amp.

P - stands for power, the unit is the Watt.

R - stands for resistance/impedance, the unit is the Ohm.

The Formulas

I = E  / R I = P  / E I =

Current

Click the unknown measurement type (Voltage/Power/Resistance), then enter the two values that you do know, and press the "Calculate Power" button to get your answer. If you have more than one value to calculate, just change the value(s) you want to adjust and click the button again (if you change to a new measurement type - make sure you click the "Reset" button first).

Which number is unknown ? Voltage  Power  Resistance

Enter Voltage Volts Enter Power Watts Enter Resistance   Ohms

Current =  Amps

Impedance/Resistance

Click the unknown measurement type (Voltage/Current/Power), then enter the two values that you do know, and press the "Calculate Power" button to get your answer. If you have more than one value to calculate, just change the value(s) you want to adjust and click the button again (if you change to a new measurement type - be sure to click the reset button or the values shown will be incorrect).

Which number is unknown ? Voltage  Current  Power

Enter Voltage Volts Enter Current Amps Enter Power Watts

Resistance/Impedance =  Ohms

Power (Watts)	Current (Amps)
Voltage (Volts)	Resistance (Ohms)

Power

Click the unknown measurement type (Voltage/Current/Resistance), then enter the two values that you do know, and press the "Calculate Power" button to get your answer. If you have more than one value to calculate, just change the value(s) you want to adjust and click the button again (if you change to a new measurement type - make sure you reset the form or the values will be incorrect).

Which number is unknown ? Voltage  Current  Resistance

Enter Voltage Volts Enter Current Amps Enter Resistance  Ohms

Power =  Watts

Planning Your System

This part of the game can be fun or disappointing depending on what you can do. First I'm going to give you an example system that I believe includes everything you need to have a pretty good system. After that I will show you how to make compromises and leave out parts that may not be as important to you to keep your system within your budget. If you want to go beyond my basic system you probably already know more than what this site can tell you. Also, you do not have to get everything at once. I put my system together over a few years. With a little planning you can upgrade your system in steps and that way its like getting a new system every time you change something instead of getting everything at once!

Basic System: This is my opinion only but I think that a good system should start off with a good head unit that either has a CD player and/or is connected to a CD changer. A good system sounds best when playing CDs, tapes just do not cut it. Next I think component sets are made with fewer compromises than coaxial speakers so I suggest getting a good midrange/tweeter set for the front. Head units generally do not put out enough clean power so you will want an amp to drive the component set. In the rear where you only need some "fill" for ambiance you can get away with cheaper coaxials and set their level lower than the fronts to keep the sound stage in front. A modest (50x4) 4 channel amp is a good choice here for powering the component set up front and the rear speakers. You could use a good 2 channel amp and run the front and back in parallel on the amp but it would harder to adjust the level between them. Midranges sound best when they do not play bass so you will want a 2 way electronic crossover and use the high pass output to drive your 4 channel amp. I did not forget the bass! Most people are happy with a single 10" woofer or a pair of 12"s. Use an appropriate enclosure and a big amp (at least 75x2, preferably even more). Throw in installation and wiring accessories (like fuses and distribution blocks). Here's an approximate price break down of what this costs in my area. Your prices may be significantly different.

head unit: $300-$500

4 channel amp for highs: $250-$400

2 channel amp for lows: $300-$700

sub(s) (1-10" to 2-12"): $150-$450

enclosure for sub(s): $0 (free air) - $250 (custom)

component set: $200-$500

coaxials for rear fill: $100-$400

crossover/equalizer: $100-$500

wiring and accessories: $50-$250

installation: $0 (do it yourself) - $100 (basic)

This comes out to $1450-$3950! I realize that this is a lot of money and that most people do not spend nearly this much money on their car stereo. However, the things listed above are what I feel is necessary to have a system with only a few compromises. If you are less concerned about highs, get coaxials in front instead of the component set and power them off of the head unit and use some bass blockers on them. This will save you about $400. Getting a bargain head unit can save you some money as well. If you are really not into bass much you can forgo all the bass related equipment and run your component set full range. This will still give you clean sound but not much bass. However, you will save $550-$2300. I would start with what I have listed above and take out parts you do not care about as much. Only you know what kind of system you can be happy with.

Please do not email me asking for recommendations about specific brands. There is a lot of equipment out there that I have not used so I will not comment on them. I am happy with the components that I have but that is as far as I can go with recommendations. When buying equipment try to spend time listening to it before you buy, especially with speakers. Also try to use equipment that is similar to yours when listening in a store. As for amps, it costs money to build a good amp so if you see some awesome price on an amp you have never heard of, it is probably a piece of junk. Stick with good names with amps.

Finally, if you are on a budget (aren't we all?) it works better to upgrade in steps.  The most important thing is to have a car audio system that sounds good to you not someone else.  If you are happy with just changing the factory speakers and stopping there then just do that.  There is a level when that new amp or speaker is not going to make a difference so it is not necessary to always upgrade.  There are people who think my system is terrible but it works well enough for me and anything else I do to it would be a minor gain and not worth my trouble.  Do not let a salesperson talk you into something you do not need!  Good luck!

Depending on your budget and personal tastes, there are many different system configurations to suit your needs.  Here's some examples:

System 1: Basic

A lot of times less is better.  Less components means lower system cost and the ability to spend a few extra bucks on the components that really count.

When it comes to sound quality, less speakers is definitely better.   The more speakers you have, the more harmful interactions and cancellation of sound waves will occur.
Start with a good set of components (two tweeters and mids) that can go down to 60 Hz with no problem in a properly designed enclosure (i.e. custom kick panel pods).  Rear speakers are not essential in most cases.

Get a good head unit with a clean signal. If most of your music is in CD format, it is better to spend your money in a good single CD player than a cheaper set of tape player/CD changer combo.

Unhappy with the front speakers sound level?  Not to worry, get a good quality amplifier.  100 watts per channel should be plenty.  Don't be too concerned about the power rating on your speakers, unless you drive speakers with ridiculously high power levels.  As long as you have good speakers and protected by a crossover with a steep slope (i.e. 24 dB/Octave) on the lower end, you should be fine.

The system should sound pretty darn good by now. If not, fix any system design/installation flaws.

Now for the last part: Bass.  You need two things: subwoofer(s) and an amplifier.  For audiophile quality sound two 10" subs will satisfy most people.  The trick is a properly designed enclosure and lots of power.  200 watts or more per sub should add plenty of punch for the bottom end of your system.

Subwoofers need more power than speakers because they are bigger and have to move more air.  If you have limited finances, go with a mid-end (i.e. Sony, Pioneer, Kenwood) amplifier for the front speakers and a better high-current amplifier for the subs.

If everything is installed properly and tweaked carefully, you will be very happy with the results.
  

System 2: Competition Level

Competition level systems require deeper pockets and more components.  System presentation also becomes a big issue.

The guidelines of the previous system apply, but you need more gear.

Head units and amplifiers need to have impeccable sound quality and no noise (background noise or alternator noise) whatsoever.  Most people prefer to take advantage of head units capable of high line level voltages (3 to 8 volts) for minimum background noise.

Equalizers become a necessity to fine tune system's response.   Most competitors prefer to use a mono 30 or 31 band equalizer per channel.   Many people have multiple sets of equalizers to quickly change the system's response from sound quality to high SPL or RTA judging.

If the audio system is to be played when the car is not running for extended periods of time, extra batteries should be added to the car.  You might need to add a high power alternator if the car's electrical system can't handle the extra loads.

All the components should be very neatly installed.  Every detail of the installation must be meticulously executed.  Wiring and connectors should be neat and clean.  The car should also be treated against rattles and road noise.
  

System 3: SPL

SPL systems are very different.  The idea here is to be as loud as possible, especially in the lower frequencies.  For a system to be loud, it needs three things:  Lots of power, a lot of speakers and a closed place where all that sound can be concentrated.  This costs, as you can imagine, plenty of money.

The first upgrade here is the vehicle's electrical system.   Alternators, capacitors and batteries become essential.

Most people into SPL competition don't consider staging and imaging as important.  Multiple speakers are placed up front, wired in series/parallel combinations to maximize amplifier power output.

A very important aspect of an SPL vehicle are the subwoofers.   Subs need to have a big cone area and high excursion (Xmax) to be able to move as much air as possible.  The amplifiers moving the subs must be able to handle high current demands and to have low impedance capability.

SPL vehicles should also be treated to be as stiff as possible to minimize loses.  Flexing body parts take a toll on output.  Serious SPL competitors replace glass with thick Plexiglas, and reinforce the whole inside of the vehicle with steel, concrete, etc.  To minimize air leaks many competitors use bolts to hold doors in place, keeping door seals tightly closed.

How Do Speakers Work?

Speakers are air pistons that move back (on the negative cycle of the signal) and forth (on the positive cycle), creating different degrees of air pressure at different frequencies. The amplifier (either separate or built-in your radio), produces electrical impulses that alternate from positive and negative voltages (AC).  This current reaches the voice coil inside the speaker, creating an electro-magnet that will either be repelled, or attracted by the fixed magnet at the bottom of the speaker.  The voice coil is attached to the cone, moving it back and forth, creating sound.  The surround (rubbery circle that joins top of the cone and metal basket) and the spider (usually yellow corrugated circle joining bottom of cone to magnet) make the cone return to its original position.

Speaker Sensitivity, measured in dB, is how loud a speaker plays (usually 1 Watt, 1 meter).  A higher Sensitivity rating means that the speaker will play louder using the same power as a speaker with a lower rating.

The back and front parts of the speaker should be isolated from each other.  When the front of the cone is pushing air, the bottom is pulling air, creating a canceling effect.  Ideally every speaker should be in an enclosure.   If you are mounting a speaker in a big hole, make sure you build a panel to isolate the front and back of the speaker (baffle).
  

Imaging, Staging and Directivity

Imaging - is being able to pick certain sounds from different places.  The singer would normally be located towards the middle of the car, guitars, trumpets, and other instruments towards the sides of the car.  If you scatter speakers all around the car your imaging would be very poor, since you would be producing the same sound at different places.  If you have a system with good imaging, the sound should seem to come from different instruments and voices, not speakers.

Staging - is the ability of a system to "fool you" into thinking that everything (including bass) is in front of you.  The sound should be similar to a stage in a concert, where the singer would be in the front center, and the rest of the instruments and background vocalists would be located to the left and right (but always on the front).

Good staging and imaging are not so easy to implement. It takes a lot experimenting with speaker location and direction.

Directivity - of sound is related to frequency.   At higher frequencies it is easier to pinpoint where the sound is coming from than lower frequencies.  This can be used to our advantage in car stereo.  Tweeters are the most important part of getting good staging.  They should be aimed towards the middle of the car.  A way to "bring" the bass to the front of the car is to fool our ears by overlapping frequencies played by midbases and subs, so that your midbases actually "pull" the bass to the front, since lower bass in not too directional.  You should crossover your midbases as low as you can (without getting distortion).  Then cut your subs at a bit higher frequency (preferably 60 HZ or less).  This will mix the bass coming from the front and rear, making the bass seem to come from the front.  Adding a center channel also improves staging, if it is set up correctly.
  

Types of Speakers

Coaxials - Coaxial speakers (or three-ways) are two (or more) speakers built-in the same frame.  They are cheaper than separate woofer and tweeters and also easier to install.  There is no need to worry about crossovers, since they are already built-in (you might still need to add a crossover to block bass if you are using high-power amplifiers).  A disadvantage of coaxials is the lack of flexibility.  For example, if the coaxial is all the way in the kick panel, or door panel aiming at your feet, you will not have good staging or imaging.  Some manufacturers try to compensate for this by making adjustable tweeters.  You should usually consider coaxial speakers for the back of the car, and separates for the front, unless you only have one speaker hole and don't plan to cut any more holes in the car.

Separates - Separates consist of a tweeter and woofer, and [most of the time] come with an external crossover.  The woofer is usually mounted in the factory hole in the door or kick panel.  The tweeters can be mounted in different places. The most common place to install tweeters is towards the top front corner of the door panel, aiming (if possible) between both front seat head rests.   Another popular location for tweeters is in the dash, either surface mounted, or in factory dash holes.  Yet another location where tweeters are commonly mounted is in the blank plastic piece on the top front side of the doors (where the mirror is on the outside).  You would have to experiment with angle and location to achieve the best possible imaging and staging.

Horns - Horns are very good at directing sound and have high efficiencies.  Horns are usually mounted under the dash.  By doing this, difference in distance from left and right speakers are greatly reduced over conventional mounting locations.  Since horns play mids and highs, tweeters are not needed.  Horns cost more than conventional speakers and require customization.  In many installations a good equalizer is required to compensate for their high sensitivity.
Horns are not for everyone though.  Many audiophiles complain of unnatural sound.   It is very hard to properly setup a set of horns.

Midbases - Midbases are usually 5, 6 or 8 inch speakers that are designed to go lower in frequency and are part of a three way system with a mid and tweeter. The problem is that 3-way arrangements require more complicated crossovers.  Midbases are most commonly mounted in the doors.

Subwoofers - Subwoofers add lower frequencies to the system.  They have to be enclosed in a box, with the exception of free air subwoofers, which use the trunk as an enclosure.  There are many different types of boxes and implementations discussed in the "subwoofers" section.
  

Mounting Locations

Front Speakers - The best place to mount speakers in the front, in custom kick panels.  By doing this, the path between the speakers and ears is minimized giving the best possible sound without having to add time delay circuitry.  If this is not possible, try to point the speakers towards the center of the car, and try to minimize the distance between the right and left speakers to your ears.  Custom kick panels are usually built from fiberglass or molded plastic, and are available from some manufacturers such as Ai Research.

Rear Speakers - Rear speakers should give a sense of space to the music, but not overpower the front speakers.  You should be able to barely hear the rear speakers.  If you are using rear speakers to add more bass/midbass to the system, at least use a crossover to cut off higher frequencies.  A lot of hi-end systems don't even have any rear speakers.  Tweeters are not necessary for the rear, a set of coaxials will work good for rear fill.

Center Channels - Center channels consist of a midrange speaker (3 or 4 inch) mounted in the middle of the dash (usually) on the top.   Center channels play a mono (Left + Right) signal between 350 - 500 and 3500 Hertz (voice range). The purpose of the center channel is to raise the sound stage, by creating the sensation of the singers "being" in the front of the car, and not in the door panels.  Center channels are hard to implement: First, a bandpass crossover is needed. Left and right channels have to be summed up.  There are various commercially available center-channel processors (many with built-in amplification).  The volume level of the center channel should be lower than the other speakers, since it is only supposed to make subtle changes to the total sound image.
  

Sizes and Shapes

There are many speaker sizes ranging from 1-inch tweeters to 18-inch (or bigger) subwoofers.  A smaller speaker will reproduce higher frequencies better than a bigger one.  The wavelength of a 20,000 Hz signal is very small, while the length of a lower (bass) note moving in the air could be as big as 40 feet.  That explains why a 4-inch speaker can't really put out bass (the lower the frequency, the more air mass that has to be moved by the speaker).  Tweeters are designed to play frequencies from 3500, 4500 or even 6000 Hz, all the way up to 20,000 Hertz.   Midranges (3, 4 or 5 inchers) play music from around 300, 500 Hz, to where the tweeters start in the upper level.  Midbases (5, 6, 8 inches) play from around 50 Hz to 500 (and even 1000) Hz.  Subs handle frequencies below 120-60 Hertz.

Do round speakers sound better than oval-shaped speakers (i.e. 6x9's)?  The answer is yes for most practical purposes. A round cone is more rigid than an oval-shaped one, so at higher levels, an oval-shaped speaker will distort more.   The reason why there are oval-shaped speakers is because of rear deck space considerations by manufacturers.  An advantage of a 6x9 speaker over a 6-inch speaker is that it has a bigger area, so it will move higher air volume, producing more bass.
  

Power Considerations

Most people think that if they use a 50 watt per channel amplifier on their factory speakers, the speakers will be damaged.  This may be true if the speakers do not have crossovers blocking off frequencies speakers were not designed to play.  What destroys speakers is distortion.  If you turn the volume all the way up on the radio, there will be distortion.  If you start hearing distortion, turn the volume down.  A high power amplifier allows the volume in the system to be higher, while the volume control on the radio is down in the range where no distortion is present.   It is better to have more power than what you need to get cleaner sound.

So how much power do you really need? As much as you can afford.   At a minimum, 30 to 50 Watts (each) would be OK for your front and rear speakers, while a little bit more (100-150 Watts) should be applied to each sub.  If you are powering up your tweeters independently, they require less power (20 - 40 Watts). Example: A four-channel set-up with separates in the front and coaxials in the rear with two subs will need about 40 Watts on each channel (Total=160W), and 100W going into each sub (Total=200W).  Notice that total power going to subs is more than total power going to the rest of the speakers.  This is because our ears are less sensitive to bass.

Subwoofer Boxes

A box ranges in complexity from the "plain vanilla box" (sealed) to bandpass and even more exotic enclosures.  Each enclosure has advantages and disadvantages and should be designed accordingly to the individual speaker parameters (the "one size fits all" rule DOES NOT apply to subwoofers and boxes).

Subwoofers need more amplifier power than everything else in the system.  This is because human ears are less sensitive at lower frequencies, so a higher bass level is needed for everything to sound even.  A low-pass crossover is required to block off high frequencies.

What type of subwoofer is better?  A bigger subwoofer gives more bass, but needs a bigger box.  Since most people like to have a trunk, 10 and 12-inch woofers are most common.  When buying a subwoofer always keep in mind that bigger size is not necessarily better.  A good quality 8-inch sub will outperform a cheap 12-incher.  Big subs (12", 15") have slower responses, yielding to boomier bass.  Small subs (8", 10") have a tight and more controlled sound.
  

Types of boxes

Free Air - subwoofers are either mounted under the rear deck or behind the rear seat of a car. This configuration will not work very well for hatchbacks. Holes have to be cut where the woofers are to be mounted. Since the woofers use the whole trunk as a box, the trunk has to be as sealed as possible from the cabin. Trunk can be isolated usually by putting particle board under the deck and behind the seat. The drawback of free air subwoofers is that bass will not be very accurate (especially at lower frequencies), and more amplifier power will be required than with a regular box, but then again, you still have a full trunk.
Sealed - is the most common box and easiest to build. These boxes will give the flattest frequency response, and best overall sound quality (especially at lower frequencies). The box internal volume should be as close as possible to the recommended by the manufacturer. If a box is smaller than what it is supposed to be, the sound will be tighter, but more amplifier power will be required. If the box is too big, then the sound will be muddy.
Ported - boxes are usually bigger in size than sealed and have a "tube" (port) that lets some air out of the box. The idea of a ported box is that the speaker port pushes (or pulls) air at the same time as the woofer, reinforcing bass. The box itself acts as an amplifier, yielding to more bass than a sealed enclosure (3 to 4 dB). Ported boxes do not have a linear frequency response.  If the box is not built according to specifications, it will not sound good. The box design acts as a filter, cutting off lower frequencies.
Isobaric - configuration is a good way to get bass in a smaller box. This is done by building a box about half the volume of a sealed box, and placing two woofers facing each other. Note that everything must be sealed, including space between woofers. A spacer between both woofers must be used in most cases to avoid subs hitting each other. When wiring, make sure that woofers are out of phase: Wire one of them backwards (negative to positive, and positive to negative), so that both pull or push at the same time. An isobaric configuration will NOT put out much more power than a box using a single woofer.  Its main purpose is to reduce box size.  Another drawback is that since one of the subs is exposed, it is more prone to damage.
Band Pass -  enclosures consist of a woofer between a sealed and ported box.  Bandpass boxes  will yield more bass than sealed and ported boxes (especially at lower frequencies), but over a narrower frequency range. Since the box acts as a filter, mechanically blocking lower and upper frequencies, a crossover is not needed in most cases.  These enclosures are usually big, and very unforgiving when precise volumes and port sizes are not followed.  Bandpass boxes also tend to mask distortion.  If you can't hear distortion and turn your stereo down in time, you could damage your subs.
Aperiodic - Very small boxes that "breathe" through a moving membrane.  Both the membrane and cone can not be in the same exterior space.  Either the membrane part has to be isolated by cutting a hole in the car so that it is outside, or the subwoofer has to be isolated from the rest of the trunk in a similar fashion to free air woofers.  The "box" has to be as small as possible (ideally the membrane should be right up against the sub), since it is used only for coupling the sub and membrane.  Aperiodic membrane configurations are very hard to design and tune, but give good frequency response and respond faster to transients, giving accurate and tight bass as opposed to boomy sound.  They are not ruled by Thiele-Small parameters like other designs, so any woofer would work with the membrane.

Amplified Bass Boxes

A good choice for small cars and (ideal) for hatchbacks and pickup trucks.  They usually take up very little room, putting out to fairly good bass. The most known manufacturer is Bazooka® for it's Bass Tubes®.  Their design is a ported box. The woofer has to be close to a wall or, better yet, to a corner.   To fine-tune, the bass tube is moved either closer, or farther form the wall or corner.

It is convenient to get an amplified tube, since amplifier, crossover and subwoofer are all integrated in a small package. If you buy the components separately, you will end up spending more money. Another good feature of tubes is the fact that they can be easily and quickly installed and removed.

If you decide to get one, keep in mind that even though they all look the same, cheaper brands will not sound good. A decent tube will run in the $300's (amplified), and in the $100's for a non-amplified.
   

Custom Bass Boxes

Many manufacturers such as JL and MTX are making custom boxes (with subs included) to fit in center consoles, under seats, or in other small spaces.  Although these boxes do cost a lot of money, most give superb performance and integrate easily in a car without taking up too much room.

Crossovers are an essential part of an audio system, often ignored.   A crossover splits frequencies so that each speaker receives a certain range of frequencies.  This is done for two reasons:

1. Avoid speaker damage: Speakers are designed to play only a certain range of frequencies. If other frequencies are played, then the speaker will produce distortion, which eventually will destroy it.
   
2. Overall balance: If a system with subwoofers, and full range speakers doesn't have a crossover, then the subs will be playing, for example, from 20 to 1000 Hz, while the full-range speakers will be playing from 60 Hz, all the way up to 20,000 Hz. As it can easily be seen, there is an "overlap" of frequencies between 50 and 1000 Hz. In this overlap region, the levels are higher than levels below 50 and above 1000Hz, yielding to a non-balanced system.

There are 3 types of crossovers:  High-pass, low-pass and band-pass.  As it can be deducted from the names, a high-pass crossover will block low frequencies, a low-pass will block high frequencies, and band-pass will block low and high frequencies below and above crossover points.

From the description above, crossover operation sounds very simple, but it is a bit more complicated.  Crossovers do not block undesired frequencies completely (unless you are using digital crossovers).  Crossovers cut frequencies progressively.  A crossover "slope" describes how effective a crossover is in blocking frequencies.  The minimum slope is 6dB/octave.  For example, a high pass crossover at 1000 Hz, will let anything above 1000Hz pass.  The farther lower frequencies are from 1000Hz the lower levels will be.  At 500 Hz (1 octave), the level at the speaker would be 6dB less.  A steeper slope (i.e. 24dB/octave) will block undesired frequencies more effectively, but will cost more than a lower slope crossover.

If a speaker will be played near it's frequency range limit, then you need a high slope.  For example, a midbass rated at 50Hz on the lower range could be crossed over at 55 or 60HZ with a 24dB/Oct crossover.  If you want to use a lower slope crossover, then the frequency would need to be higher (i.e. 100 Hz at 6dB/Oct).

So what are good crossover frequencies? It largely depends on the car, speakers, and speaker location. Typical crossover frequencies are 100Hz (bass), 350Hz (midbass), 3500 - 5000Hz (highs). For more details of what frequencies to choose, see the speakers section.
  

Active Crossovers

Active crossovers (and equalizers) need external power to operate and work at low signal voltage levels (RCAs). Signal from the head unit's RCA's is split it into low-frequencies (bass), mid-frequencies (mids), and high frequencies (tweeters), to go to different amplifiers.

What are the advantages of active crossovers? Signal is not affected as much as with passive crossovers, since everything is done at low voltages. There is much more flexibility, since all that is needed to adjust crossover frequencies is to turn a knob, while on passive crossovers, the components have to be replaced. The problem is that more amplifier channels are needed to go to all the speakers.
   

Passive Crossovers

Passive crossovers work after the amplifiers, receiving high signal levels. Since all the frequency splitting is done after the amplifiers, more speakers can run off an amplifier channel, obtaining maximum power by playing with the resistances "seen" by the amplifiers.

Passive Crossovers are capacitors and inductors either in parallel or series, or combinations that are added to cut off highs and/or lows. A capacitor stores voltage, acting as an open circuit (blocks off signal) at lower frequencies, and acts as a short at higher frequencies (lets signal pass). An inductor, on the other hand, stores current, acting in exactly the opposite way of a capacitor. Inductors act as shorts at lower frequencies, and open circuits at high frequencies.

If a capacitor is hooked up in series with a speaker, it will be a high-pass crossover (signals at lower frequencies will be blocked, and higher frequency components of the signal will be allowed to pass). An inductor in series with a speaker will be a low-pass filter. Subwoofers need inductors in series (low-pass), while midranges will need both a high-pass (cut bass off) and a low-pass (cut higher frequencies that tweeters will be taking care of). Tweeters need also high-pass filters, to block lower frequencies.

An octave is double the frequency: i.e: 20Hz --> 40Hz --> 80Hz --> 160Hz, etc. The more components are added, the more effectively the filter will be, so if both an inductor and capacitor are used, the cutoff slope will be 12 dB-per-octave, then 18 dB-per-octave, then 24 and so on.  There are many types of passive crossovers that can be implemented, starting with the capacitor or inductor in series, and getting complex as more capacitors and inductors are added.

Capacitors and inductors also dissipate power, wasting energy that speakers could be using. Low order passive crossovers are not very expensive: Capacitors run $1 - $5, inductors run $10 - $20. Higher order (i.e. 24dB/Oct) crossovers can get really expensive, especially at low frequencies/high power applications.  Passive crossovers have another drawback, that is ignored most of the time for practical purposes: They introduce phase shifts, which put voltage and current out of phase with respect to each other, affecting delivered power to the speakers and affecting overall speaker "timing".  A 6dB/Oct crossover has a phase shift of 90 degrees, 12dB/Oct = 180, 18dB/Oct = 270, 24dB/Oct = 0.  Try to stay with even-order crossovers.  If you have a 180 degree shift (2nd order crossover = 12dB/Oct, hook up the speakers out of phase (+ to - and - to +).  On 4th order crossovers (24dB/Oct), there is no phase shift.

Equalizers are used to fine tune a system, not to fix design flaws.  If you have to use a lot of equalization, there is a problem with the system that should be solved first by relocating speakers, changing crossover frequencies, amplifier gains, etc.  Equalizers are valuable instruments to flatten a system's frequency response (making the levels the same at all frequencies).  In competition, a measurement is taken on how flat the response of a system is.  More points are given to a competitor with a flatter response.  In a real system, a flat frequency response is a starting point, but does not ultimately mean perfect sound since human ears are not sensitive at the same level to all frequencies.

Many people believe that an equalizer is to boost power by raising signal levels.  95% of the time an equalizer should be used to cut levels rather than boost them.  In a well designed system the settings on an equalizer should not be too far from the zero dB line. 

Frequency

Click to View

Frequency is how many times per second a signal (AC) switches from positive to negative and back, measured in Hertz (see page on "Electrical Concepts" for a more extensive explanation).  The frequency range in which we are interested for audio is from 20 Hertz to 20,000 (20k) Hz.  The lower the frequency, the slower the signal oscillates.

The frequency spectrum is read using a logarithmic scale, and is divided in octaves (doubling of the frequency).   Octaves are for example, 20, 40, 80, 160, 315, 630 Hz and so on.  Equalizers are divided in octaves, 1/2 octaves or 1/3 octaves.  A 1 octave equalizer can only control 7-9 bands (frequencies), while a 1/2 octave equalizer can control 15 bands. A 1/3 octave equalizer would give you the most control over the system, by being able to adjust 30 -31 bands.

Q

Q is a measurement of how much the equalizer band affects a range of frequencies.  A high Q means that the EQ can control a lower "envelope" of frequencies, while a low Q is a larger envelope.  Looking at the image on the right, Q is the thickness of the affected frequencies.  A smaller Q means a wider range of frequencies boosted or cut, while a larger Q is a narrower shape.  Typical Q values are 1, 2 and 3.

Parametric vs. Graphic Equalizers

A graphic equalizer has usually fixed frequency and Q value.   The layout of a graphic equalizer is the typical sliding controls arranged by frequency.  The advantage of a graphic equalizer is that in the way it is laid out, it is easy to see what frequency is being boosted or cut and any person without much experience can adjust it.  Since a graphic EQ has fixed frequencies and Q, it has limitations on what it can control.

A parametric equalizer consists of knobs that are turned to desired levels, have adjustable frequencies and (usually) Q.  The advantage of parametric equalizers is a much greater control, since frequencies and Q values can be adjusted.  On the other hand, a parametric equalizer is much harder to adjust than a graphic EQ, requiring an experienced person and measuring equipment.

Mono and Stereo Equalizers

The main difference between mono and stereo EQs is that a mono EQ has only one input and one output, and a stereo has two inputs and two outputs.  They both have their advantages and disadvantages:   A stereo EQ controls your whole system (both left and right channels) and it is easy to adjust: Just turn the knob or slider and both left and right channels are taken care of.  If you want to adjust left and right channels independently, you can't!

A mono EQ controls only one channel, so you need two of them for the whole system.  Since you have now two EQs it takes a lot more time to setup the system.  Many people use mono EQs for the greater control they give over the system.  Since left and right speakers are not exactly at the same distance to our ears, two mono EQs can help compensate for time delays and problems caused by speaker placement.  Buying two mono equalizers is more expensive than buying one stereo EQ.

Low Level and High Level Output

A high level output equalizer takes either high level (speaker) or low level (RCA) inputs and has a built in amplifier.  The output goes directly to the speakers and can not be hooked up to another amplifier.  These equalizers are cheap and cause more damage than good to the sound system.  They do "boost" signals, but all this does is add distortion to the overall sound.

A low level input EQ takes RCA signals from the radio and has RCA outputs that get hooked up to amplifiers. Since these equalizers work at low signal levels, they introduce very little distortion, if any to the system.  They do cost more and require more wiring than a high level EQ.

A third kind of equalizer gets hooked up directly to the head unit via a special cable and is controlled by the head unit.  These EQs use low level signals and are usually of good quality.  The drawback is that if you want to upgrade the head unit or change brands, the EQ will not be compatible with other brands or even with different models from the same manufacturer.

The Head Unit is the most important part of the audio system.   You will always be staring at the head unit and touching it to control your sound system.  It is a good idea to look for something that is aesthetically pleasing, integrates to your car, has a logical button layout and has features that best suit your needs.

Head Units Features

CD Changer Controls - Whether you get a CD, cassette or MD head unit get a model that has CD changer controls, they only cost a bit more, but give you the opportunity of simply plugging in a changer in the future.

Power - Probably the most overrated feature in head units.  The power on head units is seldom given in RMS watts (see amplifiers section for definition).  Typically a head unit has an output of about 5-7 watts RMS per channel, while a high-powered head unit goes up to 13-15 watts RMS per channel (even if they claim 35 or 40 watts).

RCA Outputs - If you are planning to run the speakers from the head unit's built-in amplifier, you don't have to worry about RCAs, but if you plan to add amplifiers in the future, get one with a set of RCAs (left and right), three sets preferably (left and right for front, rear and subwoofer).  An important feature to look for is high-voltage RCA outputs.  Typically RCA signals are less than 1 volt.  High-voltage RCA signals are 2, 3 or even 4 volts.  This allows for better noise immunity and gives you a higher headroom for amplifier gain settings.  Most high-end manufacturers are selling units with high-voltage RCA outputs which are frequently used in competition.

Security - There are many security options for head units nowadays.  None of them is 100% effective in deterring theft.  Detachable faces are the most common option.  The front part of the radio comes off, rendering the rest of the unit useless.  The problem is that after a while people forget to take the face off, or simply tuck it under the seat or in the glove box.

Another option is codes, key CDs (i.e. Blaupunkt, Eclipse).  If power is cut off, the unit asks for a code or a predetermined CD used as a key.  If the incorrect code is entered, it locks the radio up, requiring service from the manufacturer.  This has proven to be an inconvenience when the owner loses their code or forget which CD they used to program the radio.  Some radios, such as Blaupunkt are using a smart card, that when removed, renders the unit useless, but again, people forget to take it out or lose it causing aggravation to the consumer.

Yet another security protection pioneered by Kenwood is a flat panel that covers the radio when the ignition key is turned off.  While this will fool some people into thinking there is no radio in, it won't fool most thieves.
  

RF modulated CD Changers

FM modulated changers can be hooked up to any radio that has an FM tuner, whether factory or aftermarket.  They use the radio's antenna to introduce the signal.  They are usually simple to hook up and consist on the changer itself which is mounted in the trunk or under seats, the control box and the display/remote control.  The drawback is that the sound of the CD changer will not be "CD quality", it will be as good as the FM tuner is.  The signal coming from the CD player has a wide frequency range but the FM tuner limits the signal, cutting the lower and upper ends of the spectrum.

Before you purchase any component, plan your system very carefully.   You need to consider if you are going to buy the whole system all at once or piece by piece, how much you want to spend and what quality and quantity of sound you want.  Are you doing a flashy or stealth installation?  Are you keeping your factory panels or are willing to cut your car to achieve better sound?   Are you doing the installation yourself, or leave it to a professional?

Sources

The most important part of the system.  Get a good head unit from a name brand.  If you skimp here, your whole system will suffer.  For people that are on a budget:  Get good quality head unit without all the bells and whistles.   A flip down face with a colorful display looks great, but it won't necessarily sound better that a regular plain head unit.  If you are planning to get amplifiers in the future, get a head unit with RCA outputs.
  

Speakers

The second most important part of the system.  If you are on a budget, just get a nice set of speakers up front and don't even worry about the rear speakers, amplifiers, etc until you have some more money later on.

Speaker installation is definitely the most important aspect that determines how your whole system sounds.  No equalizer or processor can compensate for poorly installed speakers.

Factory locations are usually not acceptable for audiophile quality sound. Speakers should ideally be pointing straight at you.   Speakers on each side should be as close to each other as possible with no obstructions. Speakers should be mounted on a good baffle (preferably an enclosure).   Difference between left and right speaker distances to your ears should be as small as possible.

The front speakers should also play as low as possible in frequency (ideally 60Hz or less), being able to handle full power.  This is where crossovers with high slopes come in to protect the speakers.
  

Amplifiers

Amplifiers do not only make a system sound louder, they make it sound BETTER.  The more power you get, the cleaner the signal going into the speakers.   A common misconception is that if a 100 watt amplifier is used on 50 watt speakers, the speakers will burn.  This is not true, as long as there is no distortion and the speakers are properly protected with crossovers.  More power is always better.

For systems with a lot of power, you might also have to upgrade the car's electrical system, by getting a high output alternator, capacitors, etc.
  

Subwoofers

Subwoofers cover low frequencies in the audio spectrum.  Subwoofers need to be installed in a box designed specifically for them.  Put a subwoofer in the wrong type or size box and it will not perform as it should and could be destroyed.

Subwoofers need a lot of power to play at acceptable levels without distortion.
  

Matching subs (and speakers) to amplifiers

This is a very important aspect of system planning that is often overlooked.  Amplifiers are designed to provide maximum power at a certain impedance.  An amplifier at this maximum level will be under more stress and produce more heat, so mounting location also becomes important.  Professional installers wire subs (and speakers) in parallel and/or series combinations to obtain a load that will make the amplifier perform at full power.
  

Processors

Many people believe that they need to have an equalizer, center channels, rear speakers, etc for better sound and compromise by buying cheaper components.  A properly designed system will sound great without the need for all this other components.

If you have the money and are an audiophile or into competition, then this "extra" components can become important.
  

Upgrading

Always keep in mind future upgrades when buying audio gear.  For example, let's say you are low on funds and want to add two subwoofers and an amplifier.   Since powerful amplifiers are expensive, you can get a 2-channel amplifier to drive the subwoofers at acceptable levels.  Later on, when you have more money, you can buy an identical amplifier and power each sub with an amplifier in bridged mode for more bass.   If you planned carefully, the impedance's of your subwoofers will match the amplifiers for maximum output in the bridged configuration.
  

Cheap Components

Buying better quality components will definitely increase system performance.  Although name brands are more expensive, they are more reliable (read: will last longer).

For people on tight budgets, it is better to save for a better component and take longer building a better system one component at a time.
  

Installation

Even though you will save money and learn something new by doing the installation yourself, sometimes it is better to pay a professional to do things that might be a bit over your head.  An experienced installer has many years of experience that will definitely make a difference in your system's performance and reliability.  If something goes wrong, you can always go back and have them fix the problem.  Many manufacturers offer and extended warranty period if the equipment is installed by an authorized professional.

Two-Way Crossover Network Design

The first and most important concept for you to understand before you design any passive crossover is that all the formulas are derived with the assumption that you are terminating into a constant impedance load. This means that the values these formulas give are only correct for the impedance value you input into the formula.  This is great if you are using a speaker with ferro-fluid (a magnetic fluid in the voice-coil gap which modifies the impedance to a relatively flat value),  however, in general a speaker's impedance varies greatly over the operating range of the driver. So before you calculate a passive crossover network, you must first correct the inherent impedance problems common in dynamic loudspeakers.

The first problem is the impedance peak present at the resonant frequency of the speaker. The exact frequency and shape of this peak is variable depending on the type of enclosure loading you are using with the driver. The graphic below will illustrate this point clearly.

As you can see, using the manufacturer's rated impedance is not a good idea. However, you can correct this impedance peak so the formulas are useful again. I would also like you to notice the impedance curving upwards in the higher frequency range. This is caused by the inductance of the voice-coil. This too can be corrected.

The first problem we will address is the peak at resonance. This can be fixed using a contour network. This filter type is covered here.

To correct the rising impedance in the higher frequencies, you need to utilize a different type of impedance shaping filter.

Explanation of Terms Used in the Formulas

C1, C2, C3, etc... are the capacitor values required for your crossover network.

L1, L2, L3, etc... are the inductor values required for your crossover network.

Rh is the impedance of the speaker at the frequency you want to apply your high pass filter.

RL is the impedance of the speaker at the frequency you want to apply your low pass filter.

f is the frequency which you are calculating the crossover for.

A bandpass filter can be used to limit how high or low the frequency range being sent to a speaker is. This can be useful when limited excursion drivers are used for the bass range in a two-way speaker system.

Links to the Calculators/Diagrams/Formulas
1st Order Butterworth
2nd Order Butterworth	2nd Order Linkwitz-Riley
3rd Order Butterworth
4th Order Butterworth	4th Order Linkwitz-Riley
6th Order Linkwitz-Riley

Driver Attenuation Circuit
This calculator is intended to help you design an "L-pad" type circuit. It can be useful if you need to attenuate (reduce) the sound level of one speaker so that it will match the output of another driver.
Shelving Network
This circuit is commonly used on tweeters because they are generally more efficient (higher sensitivity) than woofers.  It can also be applied to the "rear fill" speakers in a mobile audio application. It is very undesirable to have the soundstage in the rear of the vehicle (which will happen if your rear speakers are too loud). Note : You can accomplish this using only 1 resistor in series with the driver, however, the impedance load presented to your amplifier will be increased. When you use a L-Pad, the impedance load stays the same as it was before.
Explanation of Terms
R1, and R2 are resistors.
Calculate
To use this form, enter the impedance of the driver you want to attenuate, and then enter how many dB you want to reduce the output by (3 dB is the equivalent of cutting the power to the speaker in half). Then just click the "Calculate Values" button, and your answer will appear in the empty text boxes.
Enter Impedance Ohms Enter Desired Attenuation  dB SPL	R1 =  Ohms R2 =  Ohms

Crossover Network Design Formulas & Calculator
This calculator will design a two-way third-order Butterworth crossover network for you. If you don't understand what any of the terms mean, click here for help.
3rd Order Butterworth
High Pass Filter	Low Pass Filter
Bandpass Filter
C1 = .1061 / ( Rh x f )	L1 = (.1194 x Rh ) / f
C2 = .3183 / ( Rh x f )	L2 = (.2387 x RL ) / f
C3 = .2122 / ( RL x f )	L3 = (.0796 x RL ) / f
Calculate Your Crossover Here
To use this form, enter the impedance values (at the crossover frequency) for your speakers, and then enter the frequency you want your filter to crossover at. Now, click the "Calculate Values" button, and your results will appear in the empty text boxes.
Enter Tweeter Impedance Ohms Enter Woofer Impedance Ohms Enter Desired Crossover Frequency  Hertz
HighpassLowpass
C1 =   Microfarads L1 =   Millihenries C2 =   Microfarads	L2 =   Millihenries C3 =   Microfarads L3 =   Millihenries

Series Notch Filters  A series notch filter can be used to control the impedance peak present at the resonant frequency (Fs) of a speaker. For an explanation of loudspeaker impedance and passive crossovers, click here. If your driver has Ferrofluid in the voice-coil gap, this circuit will not be beneficial because the peak at resonance is controlled mechanically. A high-pass crossover with a corner frequency (the frequency utilized in the crossover network design) less than two octaves above the resonance of the driver will not function properly. All crossover design formulas are accurate only when the loudspeaker impedance is at the level specified in the formula. If the impedance is higher/lower than the value used in the formula, the filter roll-off is affected.  The black line in the image below shows the impedance curve of a speaker in a closed box. The red line shows the impedance of the same speaker/enclosure combination with a properly designed series notch filter.  The upward curve at higher frequencies is caused by the voice-coil inductance and is corrected using a Zobel or parallel notch filter. When you design a crossover from a formula and apply it in a situation similar to the one above, the results are less than spectacular.  For this simulation, I modeled a driver whose resonant frequency (Fs) is 53 Hz. The component values were determined using 8 ohms for impedance and 200 Hz for the crossover frequency. This frequency was chosen so it would be close enough to the resonance of the driver that the crossover would be affected by it.  The following image shows the desired response for a second-order Linkwitz-Riley crossover network in red. The black curve is the response you would obtain if you used the components specified by the crossover design formulas without impedance correction.  The third graphic shows how much closer to the desired response you will get by correcting the impedance of the driver. The crossover filter goes in the circuit before the notch filter (closer to the source). The Formulas C is the value for the capacitor L is the value for the inductor. R is the value for the resistor. Calculate Your Series Notch Filter Here  To use this calculator, enter the values of Fs, Qes, Qms, and Re for your speaker. Then click the "Calculate" button and the values will show up in the boxes below. Fs : Hz Qes : Qms : Re : Ohms C :  uF L :  mH R :  Ohms   This type of filter is generally used on midranges/tweeters. It can however, be used on woofers, but the component values required are large and would be very expensive.

Crossover Network Design Formulas & Calculator
This calculator will design a two-way second-order Linkwitz-Riley crossover network for you. If you don't understand what any of the terms mean, click here for help.
Please note the reversed polarity wiring on the high pass filter. Second-order filters will usually give you a better overall frequency response when they are wired this way because this type of filter shifts the phase of the input signal 180°.
2nd Order Linkwitz-Riley
Second-Order High Pass Filter	Second-Order Low Pass Filter
Second-Order Linkwitz-Riley Bandpass Filter
C1 = .0796 / ( Rh x f )	L1 = (.3183 x Rh ) / f
C2 = .0796 / ( RL x f )	L2 = (.3183 x RL ) / f
Calculate Your Crossover Here
To use this form, enter the impedance values (at the crossover frequency) for your speakers, and then enter the frequency you want your filter to crossover at. Now, click the "Calculate Values" button, and your results will appear in the empty text boxes.
Enter Tweeter Impedance Ohms Enter Woofer Impedance Ohms Enter Desired Crossover Frequency  Hertz
HighpassLowpass
C1 =  Microfarads L1 =  Millihenries	C2 =   Microfarads L2 =   Millihenries

Crossover Network Design Formulas & Calculator
This calculator will design a two-way sixth-order Linkwitz-Riley crossover network for you. If you don't understand what any of the terms mean, click here for help.
6th Order Linkwitz-Riley
Sixth-Order High Pass Filter	Sixth-Order Low Pass Filter
Sixth-Order Linkwitz-Riley Bandpass Crossover Filter
C1 = .08841 / ( Rh x f )	L1 = (.08594 x Rh ) / f
C2 = .10810 / ( Rh x f )	L2 = (.14200 x Rh ) / f
C3 = .21880 / ( Rh x f )	L3 = (.63660 x Rh ) / f
C4 = .29470 / ( RL x f )	L4 = (.28650 x RL ) / f
C5 = .17830 / ( RL x f )	L5 = (.23440 x RL ) / f
C6 = .03979 / ( RL x f )	L6 = (.11570 x RL ) / f
Calculate Your Crossover Here
To use this form, enter the impedance values (at the crossover frequency) for your speakers, and then enter the frequency you want your filter to crossover at. Now, click the "Calculate Values" button, and your results will appear in the empty text boxes.
Enter Tweeter Impedance Ohms Enter Woofer Impedance Ohms Enter Desired Crossover Frequency  Hertz
HighpassLowpass
C1 =   Microfarads L1 =  Millihenries C2 =   Microfarads L2 =  Millihenries C3 =   Microfarads L3 =  Millihenries	C4 =   Microfarads L4 =  Millihenries C5 =   Microfarads L5 =  Millihenries C6 =   Microfarads L6 =  Millihenries

Zobel Loudspeaker Impedance Correction Circuit
This page will help you understand what a Zobel filter does, and how it can be useful in a loudspeaker crossover network design. If you need more help, click here.
A "Zobel" circuit can correct the rising impedance load presented to the amplifier. This allows a speaker to reproduce high frequencies better because more power is available for the driver due to the fact that the impedance is relatively constant. It also helps to keep the crossover point from shifting due to impedance variations.
The cause of this impedance rise is the inductance of the voice-coil of the speaker. A voice-coil is a coil of wire wrapped around the former (which is connected to the back of the cone.) It looks like an inductor wound with small gauge wire. The reason inductors are used in crossover design is because the impedance of an inductor increases as the frequency of the signal applied to it goes up. This reduces the power applied to the speaker at higher frequencies. This is how an inductor "rolls-off" the sound.
The line with an impedance of approximately 37.5 ohms around 2000 Hz is this driver resonant frequency (Fs). The plot with the greatest impedance centered at approximately 1350 Hz is the impedance of the same speaker with a Zobel filter. Notice on this driver the Zobel filter also lowered the impedance at resonance. Since a flat impedance curve is very desirable, I altered the component values so this one filter is could do the work of two (the lowest line). This reduced the component count of the impedance correction portion of this crossover network from five to two!
The other (unnecessary in this case) filter is a resonance equalization circuit. This speaker is a good example of how useful a crossover design program can be. The crossover design equations are all useful to get in the "ballpark", but if you are going to design advanced crossover networks, you need a good program to see what is really happening in your crossover. Personally I use CALSOD™ from Audiosoft, L.E.A.P.™ is generally regarded as the best loudspeaker design program available, but I can't afford it yet. Maybe someday :).
Explanation of Terms Le is the inductance of your driver's voice-coil (in henries). Re is the D.C. resistance of the voice-coil (ohms). The design equations for this type of filter are: Capacitor = Le/Rc2 Resistor (Rc) = 1.25 X Re	Zobel Filter Diagram
The Formulas and the Calculator
To use this calculator, enter the D.C. resistance and the inductance of your driver, click the "Calculate Values" button and the required component values will appear in the remaining text boxes.
Enter D.C. Resistance Ohms Enter Voice-Coil Inductance  Millihenries	Capacitor =  Microfarads Resistor = Ohms

Crossover Network Design Formulas & Calculator
This calculator will design a two-way fourth-order Linkwitz-Riley crossover network for you. If you don't understand what any of the terms mean, click here for help.
4th Order Linkwitz-Riley
Fourth-Order High Pass Filter	Fourth-Order Low Pass Filter
Linkwitz-Riley Bandpass Filter
C1 = .0844 / ( Rh x f )	L1 = (.1000 x Rh ) / f
C2 = .1688 / ( Rh x f )	L2 = (.4501 x Rh ) / f
C3 = .2533 / ( RL x f )	L3 = (.3000 x RL ) / f
C4 = .0563 / ( RL x f )	L4 = (.1500 x RL ) / f
Calculate Your Crossover Here
To use this form, enter the impedance values (at the crossover frequency) for your speakers, and then enter the frequency you want your filter to crossover at. Now, click the "Calculate Values" button, and your results will appear in the empty text boxes.
Enter Tweeter Impedance Ohms Enter Woofer Impedance Ohms Enter Desired Crossover Frequency  Hertz
HighpassLowpass
C1 =   Microfarads L1 =  Millihenries C2 =   Microfarads L2 =  Millihenries	C3 =   Microfarads L3 =   Millihenries C4 =   Microfarads L4 =   Millihenries

Parallel Notch Filter Circuit
Explanation of Terms
C is the capacitor value required for your filter.
L is the required inductor value for your filter.
R is the desired resistor value for this filter.
F is the frequency (in Hertz) halfway between F1 and F2.
F1 is the frequency point below F that is -3dB SPL relative to F.
F2 is the frequency point above F that is -3dB SPL relative to F.
For the example driver below, the center point of the response peak (F) would be at about 3583 (Hertz). F1 and F2 would be located at approximately 1015 and 6150 respectively.
Frequency Response Example
At first glance, the response of the speaker above does not look like a very good candidate for a driver in a quality loudspeaker system. A broad peak in the frequency response of a speaker like the example above can be easily corrected through the use of a notch filter, however.
Note : This filter can be used on any type of speaker, it is not only for midranges - this was just an easy example to model.
If you need some logarithmic paper to aid in your SPL measurements, I have made two graphics to help. The first one can be used for low frequency plotting, and the second is a full-range scale. Just click the link for the one you need, and press the "print button" on your browser after the image is done loading. I will add some notes about the methods used to properly measure frequency response as soon as I can.
Calculate Your Notch Filter
To use this form, enter F, F1, and F2. Then, click the "Calculate Values" button, and your results will appear in the empty text boxes.
Enter F Hertz Enter F1 Hertz Enter F2 Hertz	C =  Microfarads L = Millihenries R = Ohms