Next to the head-unit, your speakers are the most important part of your audio system. Here's how you can get the most from them:

The biggest improvement in car audio systems occurred when auto manufacturers started building cars with more powerful head-units and multiple speakers. These early “surround systems” featured front and rear speakers on the left and right, placing larger speakers in the rear to provide dimension and extra bass.

But these systems were lacking since a single speaker cannot be used to effectively reproduce the full range of sounds. If the speaker is too large, then it cannot reproduce high frequencies that require rapid movement of the speaker. If the speaker is too small, then it cannot reproduce low frequencies that require large amounts of air to be moved.

Tweeters are usually very small, ranging in size from 1/2" to 2" in size. Tweeters larger than 1" in size cannot respond quickly enough to produce quality sound, and they are too directional for car audio.

Although tweeters are very small, they need to be mounted where they fire directly at you (“on-axis”) or they may not be heard properly. Some tweeters have better off axis response than others, so they sound good even if they are not directed towards you.

TIP: If you will not be on axis with the tweeter when you evaluate them, listen to how their sound changes as you move around the tweeter to determine how it will sound in your car.

Most BMW’s equipped with tweeters are on-axis in the front, since they are mounted in the A-Piller. The tweeters in the rear are usually contained in a special enclosure in the rear deck with a larger speaker, and they are off-axis. Most tweeters are ¾” in size, and they can be easily replaced.

A further division in frequency can be made, but it usually complicates the “crossover” that separates the full audio signal into multiple parts for each speaker.

For tweeters and midranges, power handling is not as important as it is with woofers since it does not take much power for them to play loudly. Midranges should fit within the door, dash or rear panel space provided or you will have to do some cutting or fabrication.

Kickpanels for midranges and tweeters (or coaxials) offer better imaging than locations in the door; but the soundstage is sometimes lower than when you have the tweeters mounted high in the doors or on the A pillars.

Because a woofer must move large amounts of air, woofers today are usually large with typical sizes of 8”, 10" and 12". As speaker technology advances and amplifiers produce more power, we can expect woofer sizes of 15”, 18”, 21” and higher to be more common.

TIP: Use the specs of the woofer as a guide so you can create the type of bass response you desire. Be careful to match the specs of the woofer and the amp driving it.

Most woofers are contained in boxes called enclosures.

Sensitivity

Sensitivity is a very important specification for a speaker. Sensitivity 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, then 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.