| |
Car Stereo 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 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 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
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
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
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
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.
Horns
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
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.
Mounting Locations
Front Speakers
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
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 120 Hertz.
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.
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.
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.
Wiring
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).
Parallel Resistance:
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 an expert.
Series Resistance:
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
individual resistances:
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.
Noise
Ordinance
A noise ordinance is a law created at local levels that
pertains to the amount of noise, duration of noise,
and source of sounds other than ambient noise that affect
a community’s inhabitants. Basically, a noise ordinance
defines which sounds are and are not acceptable at any
given time so that residents can live comfortably within
a community in terms of the sounds that they hear. A
city or county noise ordinance is usually effective
during certain times of the day. A noise ordinance typically
applies at night during the times when most people sleep.
Violations of a noise ordinance are often reported to
police or local officials by individuals who are disturbed
by sound and feel that an ordinance has been violated.
You may need to
hire an lawyer
with your case
|
