Car Audio Basics - 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:
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
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.
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