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
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
Imaging, Staging and
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
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
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
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
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
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
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
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