Specifications

180
changes. This is known as a delay or phase shift.
The graph below shows a phase shift between
two sine waves.
The goal of a high quality car audio system is
to accurately reproduce the sound of a musical
performance. When sound is recorded in stereo
(two channels), it is of the utmost importance
that the sound coming from each channel arrives
at the listeners ear simultaneously. This can be
achieved through proper speaker placement,
or compensated for by using time alignment or
digital delays.
Octave
An Octave is a way of describing a doubling or
halving of a frequency. If a 1,000Hz (1kHz) tone
is being played, and a second tone starts one
octave higher, it will be at 2.0 kHz. If the second
tone were an octave lower, it would be at 500Hz
(0.5 kHz).
Decibel
This is one of the most misunderstood terms in
modern audio discussions. The BEL is the unit
of measure used to describe sound intensity. It
was first defined by Alexander Graham Bell. The
Bel is an extremely large unit of measure, so the
Decibel unit is more commonly used. 1 Decibel
(dB) is equal to 0.1 Bel.
The Decibel was created in response to numerous
tests on human hearing to describe sound
intensities (volume).
1dB = The smallest perceivable change in intensity
within the most sensitive range of human hearing
(between 3 and 4 kHz)
3dB = The smallest perceivable difference in
intensity at all frequencies.
10dB = A perceived doubling or halving of sound
intensity
In terms of electrical signals, decibels can still
be used to describe the difference between two
voltages or amplitudes. This is quite convenient
when talking about power coming from an
amplifier, since each time we want to increase
the perceived output from a speaker system by
3dB, we need to double the power coming from
an amp.
Example: A speaker has an efficiency rating of
88dB 1W/1M. This means that when this speaker
is installed in an infinite baffle (the wall of a very
large room for example) and powered with 1Watt
of power, it will produce 88dB of sound. If we
want to increase the output of this speaker to
91dB, we need 2Watts of power from the amp.
The following chart outlines the power required
for this speaker to reproduce different sound
levels:
Reference - 88dB 1W/1M
Output Level Power (Watts) Relative difference
118 1024 +30dB
115 512 +27dB
112 256 +24dB
109 128 +21dB
106 64 +18dB
103 32 +15dB
100 16 +12dB
97 8 +9dB
94 4 +6dB
91 2 +3dB
88 1 0dB
85 0.5 -3dB
82 0.25 -6dB
79 0.125 -9dB
76 0.0625 -12dB
73 0.03125 -15dB
70 0.015625 -18dB
67 0.0078125 -21dB
64 0.00390625 -24dB
61 0.001953125 -27dB
58 0.000976563 -30dB
You can see that the power being produced by an
amplifier needs to vary over an enormous range to
reproduce music at different listening levels. You
can also see that significant amounts of power
are required to reproduce realistic listening levels,
which is why high quality car audio amplifiers are
very important.
Car Audio Reference Guide