Description

This article is from the Car Audio FAQ, by Ian D. Bjorhovde (ianbjor@mobileaudio.com) with numerous contributions by others.

3.4 What do all of those specifications on amplifiers mean? [JSC, BG]

"Frequency response" refers to the range of frequencies which the
amplifier can reproduce within a certain power range, usually +/-3dB.

"Continuous power output" is the power output of the amplifier into one
channel into a certain load (usually four ohms) below a certain
distortion level (usually at most 1%THD) at a certain frequency
(usually 1kHz). A complete power specification should include all of
this information, e.g. "20W/ch into 4 ohms at < 0.03%THD at 1kHz"
although this can also be stated as (and be assumed equivalent to)
"20W/ch at < 0.03%THD". The amplifier should also be able to sustain
this power level for long periods of time without difficulties such as
overheating.

"Peak power output" is the power output of the amplifier into one
channel into a certain load (usually four ohms) below a certain
distortion level (usually much higher than the continuous rating level)
at a certain frequency (usually 1kHz). A complete power specification
should include all of this information, e.g. "35W/ch into 4 ohms at <
10.0%THD at 1kHz" although this can also be stated as (and be assumed
equivalent to) "35Wch at < 10.0%THD". Consumer warning: some
manufacturers will state the "peak power output" rating by including
the amount of power which can be drawn from "headroom", which means
power supply capacitors. They usually will not tell you this in the
specification, however; indeed, they tend to prominently display the
figure in big, bold letters on the front of the box, such as "MAXIMUM
200W PER CHANNEL!!!" when the continuous rating is 15W/ch and the unit
has a 5A fuse.

"Damping factor" represents the ratio of the load being driven (that
is, the speaker - usually four ohms) to the output impedance of the
amplifier (that is, the output impedance of the transistors which drive
the speakers). The lower the output impedance, the higher the damping
factor. Higher damping factors indicate a greater ability to help
control the motion of the cone of the speaker which is being driven.
When this motion is tightly controlled, a greater transient response is
evident in the system, which most people refer to as a "tight" or
"crisp" sound. Damping factors above 100 are generally regarded as
good.

"Signal to Noise" or "S/N" is the ratio, usually expressed in decibels,
of the amount of true amplified output of the amplifier to the amount
of extraneous noise injected into the signal. S/N ratios above 90 to
95dB are generally regarded as good.

Continue to:

• prev: 3.3 What are some good (and bad) brands of speakers? [JSC]
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• next: 3.5 What does "bridging an amp" mean? [MHa]