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 speaker (baffle).
Imaging And Staging
Imaging is being able to pick certain sounds from certain places.
The singer would normally be located towards the middle of the
car, in a car audio installation, guitars, trumpets, and other
instruments towards the sides of the car, in a car audio installation.
If you scatter speakers all around the car, in a car audio installation,
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 speakers.
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
the front). Good staging and imaging are not so easy to implement
in a car audio installation. 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 audio
installation. Tweeters are the most important part of getting
good staging. They should be aimed towards the middle of the car,
in a car audio installation. A way to "bring" the bass to the
front of the car is to fool our ears by overlapping frequencies
played by midbass and subs, so that your midbass actually "pull"
the bass to the front, since lower bass in not too directional.
You should crossover your midbass as low as you can (without getting
distortion). Then cut your subs at a bit higher frequency. 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, in your car audio installation.
Types of Speakers
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 coaxial 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, not your ears. Some manufacturers try to
compensate for this by making adjustable tweeters. You should
usually consider coaxial speakers for the back of the car, in
a car audio installation, and separates for the front, unless
you only have one speaker hole and don't plan to cut any more
holes in the car, for the audio installation.
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 staging.
Midbass 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. A well-balanced three-way set up
will give you accurate imaging and staging. Midbass are most commonly
mounted in the doors.
Subwoofers add lower frequencies to the whole system. They have
to be enclosed in a box, with the exception of free air subwoofers,
which use the trunk as a box. There are many different types of
boxes and implementations discussed in the subwoofers section.
A few high-end manufacturers are making horns for car audio use.
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. Even though horns are mounted under the
dash, they give great imaging. Horns cost more than conventional
speakers and require customization. In many installations a good
equalizer is required to compensate for their high sensitivity.
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, in a car audio installation, and not
in the door panels. Center channels are hard to implement though:
First, a band pass 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.
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, in a car audio installation,
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 Research.
Rear speakers should give a sense of space to the music, but not
overpower the front speakers. If you are using rear speakers to
add more bass to the system, at least use a crossover to cut off
higher frequencies. You should be able to barely hear the rear
speakers. A lot of hi-end systems don't even have any rear speakers.
Separates are not necessary for the rear, a set of coaxials will
work good for rear fill.
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 inchs)
play music from around 300, 500 Hz, to where the tweeters start
in the upper level. Midbass (5, 6, 8 inches) play from around
50 Hz to 500 (and even 1000) Hz. Subs handle frequencies below
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 bass.
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? 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 bass.
A trick that professional car audio installers use to get more
power out of amplifiers is to wire up speakers in different ways,
playing with resistances to achieve a desired total impedance
"seen" by the amplifier. Even though speakers are active loads
(resistance changes with frequency), it is accepted to treat speakers
as resistors with a fixed resistance value (usually 4 ohms).
People commonly hook up two or more speakers to the same channel
out of an amplifier in parallel. This is achieved by hooking up
the negative wire from the amp to all the negative connections
of the speakers, and the positive to all the positive connections
of the speakers. By doing this, the load seen by the amplifier
is lower. For example, if two 4-ohm speakers are wired-up in parallel,
then their total resistance will be half, or 2 ohms. If three
speakers are wired up in parallel, and they all have the same
resistance value, then the total load would be a third of the
value of each speaker's resistance. Here's a formula to calculate
parallel total resistance for two speakers:
For more than two speakers, use the following formula:
So what are the advantages and disadvantages of this scheme? First,
if one of the speakers burns out, then the other one (s) keep
playing. If the amplifier is not designed to receive lower loads
provided by hooking the speakers up in this fashion, you might
end up destroying your amplifier. Check your manual or consult
Speakers are hooked up in series to decrease total load to an
amplifier. To hook up speakers in series, connect the positive
terminal of the amplifier to positive of one speaker, then hook
up negative of that speaker to positive of next speaker, and so
on. Then hook up negative of last speaker to negative of the amp.
It is a lot easier to calculate total resistance for speakers
hooked up in series. This is easily done by adding up all the
The disadvantage of hooking up speakers in series other than getting
less power out of an amplifier, is that if one of the speakers
burns up, the other one (s) stop working.
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