Speakers Overview:
The car speakers you use will have the absolute say in how your system will sound. There are many different 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 great it will have problems reproducing high frequencies which require rapid movement of the speaker. If it is too diminutive 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 imitates 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 fast. Very little power is required for powering tweeters because they are very efficient. Woofers are the exact opposite because they usually require considerable 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 considerable 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 fast enough to sound good and are too directional. In between are midrange speakers which handle the frequencies between the woofers and tweeters. Further separation can be done but is usually unrequired 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 pivotal here. Some manufacturers will assert 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 critical 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 specification 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 greater 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 regular. If you use anything outside of this range you may have trouble matching the output levels of the speakers relative to each other. .

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 correctly. 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 variates 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 greater the woofer the larger the enclosure required to hold it. Some woofers are better optimized for modest 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.

How Do Speakers Work?
Moving Speaker Speakers are air pistons that move back (on the negative cycle of the signal) and forth (on the positive cycle), creating varied degrees of air pressure at different frequencies. The amplifier (either separate or built-in your radio), produces electrical impulses that change from positive and negative voltages (AC). This current reaches the voice coil inside the speaker, forming 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 separated from each other. When the front of the cone is pushing air, the bottom is pulling air, creating a cancelling effect. Ideally each speaker should be in an enclosure. If you are mounting a speaker in a big hole, make certain 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 usually 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 bad, since you would be producing the same sound at different places. If you have a system with flawless 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 feeling that everything (including bass) is in front of you. The sound should be identical 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 simpler 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. You should usually consider coaxial speakers for the back and the front of the car, 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. Typically they are installed towards the top front corner of the door panel, in the dash or the 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 typically 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. Horns are not for everyone though. It is not easy 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. Midbases are usually 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.

Car Speaker Mounting Locations
Front Speakers – The best place to mount speakers in the front, in custom kick panels. If this is impossible, 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 .

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. Most high end systems don’t have rear speakers. Tweeters are not essential for the rear, a set of coaxials will work well 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 need of the center channel is to raise the sound stage, by causing the sensation of the singers “being” in the front of the car, and not in the door panels. Center channels are hard to implement.

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.

Do round speakers sound superior than oval-shaped speakers (i.e. 6×9’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 6×9 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. 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.