Car audio head units in all basic factory car stereo systems Northern NJ have small, built-in amplifiers to power a handful of speakers.
Meanwhile, premium factory-installed sound systems usually use larger, more
powerful "outboard" amplifiers that are separate from the head unit
to power more speakers and achieve better sound quality.
An amplifier is typically buried in the car,
you'll rarely see it in an OEM (original equipment manufacturer) sound system
like you would a head unit and speakers. But amplifiers are integral components
that provide power and volume to your car tunes, and they play an important
part in the character of the music you experience in your car. Without an
amplifier, you could never experience high-quality music reproduction in your
car.
Boosting
Amplifier boosts the low-level audio signal generated by the head unit so that it's powerful enough to move the cones of the speakers in the system and create sound. But before the signal can be amplified, it has to be processed by a preamplifier or "preamp."
There can be more than one preamp component in
a complex car audio system. Preamp refers to any stage in the audio path in
which the signal is processed before being amplified. The preamp inside a head
unit takes the raw signals from the various sources in the head unit, such as
the CD player or radio tuner, and sends the low-level output to the amplifier. The
preamp stage is also where such tone controls as bass, treble and equalization
manipulate the audio signal that will ultimately adjust the sound. When the
signal reaches the actual amplifier, its internal-input preamp stage processes
it further.
Crossing Over
Part of the preamp processing typically
involves circuitry known as a crossover. It electronically divides the
full-range audio signal that's fed to the amplifier into separate frequencies.
Think of a crossover as an audio-signal traffic cop, directing specific
frequencies so they can be reproduced by specialized speakers, such as woofers
and tweeters.
Many car stereo systems Northern NJ use two types of
crossovers. An active crossover is a preamp component that divides the
full-range, line-level signal before
amplification so an amplifier or an amplifier's separate channels handle only a
certain frequency range for specific speakers. A passive crossover accepts an
audio signal after it's been
amplified and siphons off frequencies for specific speakers. Passive crossovers
are found on "two-way" speakers that have a pair of speakers mounted
on a single frame. A two-way 6-by-9-inch speaker that's found in many stock
audio systems incorporates a large midrange and small tweeter. In that case, an
audio signal will first pass through a small passive crossover that separates
the frequencies between the two speakers.
The Speakers
While almost any amplifier will produce
around twice its RMS power in peak mode, it's usually with very high
distortion. This occurs when the amplifier is pushed to its limits and creates
severely distorted sound that can damage a system's speakers. When a car stereo
system suffers from distortion, your first impression may be to blame it on
defective speakers. But in reality it's more likely caused by distortion from
the amplifier. The small amplifiers built inside of head units or even some
outboard amps in OEM sound systems are not always up to the task of cranking
out tunes at very loud volumes.
