Specifications

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Car Audio Reference Guide
Car Audio Physics
Understanding some basic fundamentals of
physics are required to sell and install car audio
products.
Sound
Sound is essentially changes in air pressure.
These compressions and rarefactions cause
minute bones inside our ears to vibrate, which
our brains translate into perceived sound.
The chart above shows an electrical representa-
tion of a spoken conversation. The high points
represent high sound levels and low areas repre-
sent little or no sound.
Frequency
If you look at sound using an oscilloscope, you
can see the voltage moving up and down relative
to time. If you are listening to a pure tone - like the
'test tone' on your TV in the middle of the night,
then waveform will look something like the graph
below.
Period
The period is the amount of time between two
identical points on a repeating waveform. We
measure this in seconds (or milliseconds. If you
take the reciprocal of this number, you get fre-
quency. For example - If you measure a period
using a scope of 0.025 seconds, then take the
reciprocal (1/0.025) you will see the frequency is
40Hz.
Amplitude
The Amplitude of a sound describes its intensity,
loudness or strength. Later on we will explain the
Decibel scale and how it relates to sound pres-
sure measurement and observation.
Frequency Response
If you look at the sound coming from a speaker,
you want all the different sounds to be repro-
duced at the same level. This is known as the
frequency response of a speaker. A frequency
response graph, shows the output level (of a
speaker, amplifier, source unit, etc). The X-axis
represents the different frequencies measure and
the Y-axis represents how strong the output is.
Ideally, a speaker would produce all frequencies
at exactly the same level, but due to the physical
limitations of every speaker, this is not possible.
The graph below shows the frequency response
of a typical high-quality full-range speaker.
Phase
Phase refers to the time between - or relative
arrival time of two signals or waveforms. Imagine
two speakers playing the exactly same sound,
set up in your living room. If you were to take one
speaker and move it further away from you, the
time it takes for the sound to arrive at your ears