Choosing Speakers

The speakers you use will have the final say in how your system will sound. There are many types of speakers available. A single speaker can be used to reproduce the full range of sounds but it is not ideal. If the speaker is too large it will have problems reproducing high frequencies which require rapid movement of the speaker. If it is too small it will have problems reproducing low frequencies which require large amounts of air to be moved. Because a single speaker cannot reproduce all sounds accurately multiple speakers are used each of which reproduces sound in the frequency range it was designed for. A speaker called a tweeter reproduces high frequencies generally above 2 kHz. Tweeters are small and lightweight so they can respond quickly. Very little power is required for powering tweeters because they are very efficient. Woofers are the exact opposite because they usually require large amounts of power to really move air. Woofers are meant to produce sound at frequencies below 250 Hz and often just below 100 Hz (in the case of subwoofers). Because a woofer must move large amounts of air they are usually large with typical sizes of 10", 12", 15" and even 18"! On the other hand tweeters are usually very small ranging in size from 1/2" to 2" in size. Typically, tweeters larger than 1" in size cannot respond quickly enough to sound good and are too directional. In between are midrange speakers which handle the frequencies between the woofers and tweeters. Further division can be done but is usually unnecessary and just complicates the crossover which must separate the full audio signal into multiple parts for each speaker.

Things to look for:

Power Handling: Just as with amplifiers, RMS or continuous power is important here. Some manufacturers will claim very high power handling figures but they are usually for very short peaks only. Granted music is not continuous but the continuous power handling gives you a much better impression of how much power a speaker can really handle. For tweeters and midranges, power handling is not as important since it does not take much power for them to play loudly. For woofers though a rough match should be made between the woofer and the amp driving it.

Sensitivity:This is a very important spec for a speaker. It gives you an idea of how loud a speaker will play given a certain input power. If a speaker is insensitive then it will require more power to play at the same volume level than a speaker that is more sensitive. Figures between 85 dB and 95 dB at 1 watt RMS at 1 meter are common. If you use anything outside of this range you may have problems matching the output levels of the speakers relative to each other. If you're going to run speakers off of a head unit then try to get speakers with higher input sensitivities since head units typically do not have much power.

Physical Size: You must pay attention to the size of the speakers you choose. Tweeters are very small but need to mounted where they fire nearly directly at you or they may not be heard properly. Some tweeters have better off axis response than others. If you will not be on axis with the tweeter when you audition tweeters in a store listen to how their sound changes as you move around them to see if they will work in your car. Midranges should fit in the door or dash spaces provided or you will have to do some cutting or fabrication. In general the larger the woofer the larger the enclosure required to hold it. Some woofers are better optimized for small enclosures than others (Kicker Solobaric, JL Audio W6 for example). Make sure you have enough room in your trunk or hatchback for the woofer. Kickpanels for midranges and tweeters or coaxials typically offer better imaging than locations in the door however the soundstage is sometimes lower than when you have the tweeters mounted high in the doors or on the A pillars.

Enclosures for Woofers:Because woofers move a lot of air they generate a back wave behind them.  If you mount a woofer in free space without an enclosure you will get almost no bass because the back wave will cancel out the sound from the front of the woofer.  There are many types of enclosures for woofers to handle this backwave. A popular one is a ported box. This enclosure has the woofer mounted in box with a hole in it and a port (tube) attached to the hole. The port is made a specific size and depth to cause a "bump" or rise in the frequency response at that point. This makes the overall system more efficient but can cause the bass to be somewhat "boomy" or less "tight" depending on how its done. A newer technique is a bandpass enclosure. The woofer is mounted inside the box and fires into another chamber within the box that is ported to the outside. Again, this increases efficiency greatly but only at a certain frequency. This effect can make the system very loud and boomy. Another method employs mounting the woofer (which needs to be a free air type in this case) to the rear deck of the car and using the trunk as a big box. This method is subject to many variables but can work well if done properly. Another benefit of this method is that you do not lose space from a large enclosure box. The oldest and most popular type is a sealed enclosure. This method simply has the woofer firing into the car and the back wave is suppressed inside the box. This method usually produces tight accurate bass but is not as efficient. Also this method typically requires a large box to work well. Finally because of the lower efficiency of this design more powerful amps and woofers are needed to play loudly. When any of these enclosures are created using the specs of the woofer as a guide you can create the type of bass response that you desire.