Primer
Crestron
Surround Sound
Low frequency sounds have long wavelengths and high frequency
sounds have short wavelengths. The length of a 20 Hz sound wave is
about 56 feet. Speakers that produce low frequencies must therefore be
large in size with long excursions (the distance a speaker moves in and
out) to produce large and long waves. Speakers producing high
frequency sounds must be small enough to move rapidly and produce
the very small waves of high frequencies (about two thirds of an inch at
20 kHz).
Wavelength and Amplitude
Volume (Amplitude)
Volume is the relative loudness or power of an audio signal resulting
from the amplitude of a sound wave. Amplitude is the vertical distance
from zero to the highest point or peak. Sound waves with higher
amplitudes carry more acoustic power and therefore higher volume.
Volume is measured in units called decibels (dB). A dB is one-tenth of
a Bel, named in part after Alexander Graham Bell (the “B” is
capitalized for Bell) and is used in both audio and video applications.
Decibel is a logarithmic scale measuring the intensity (pressure level)
of sound. Decibels are ratios, not fixed quantities. Decibels are also
referred to as a measurement of "gain" with respect to amplifiers (refer
to the glossary).
For the non-linear human ear to perceive a sound that seems twice as
loud, a ten-decibel (10 dB) increase doubles the sound pressure level,
20dB is twice the sound level of 10dB, and 30dB is twice as loud as
20dB. 40dB is twice the sound level of 30dB and four times the sound
level of 20 decibels.
With some kinds of equipment, such as microphones, analog tape
recorders, or LP playback systems, the dB measurement is "weighted"
as to audibility, because the ear is more sensitive to particular
frequencies. Two common corrections for hearing characteristics are
the A-weighted and the more rigorous C-weighted scales, indicated as
dBA or dBC, respectively.
The term decibel is also used in various other measurements such as
signal-to-noise ratio, gain and dynamic headroom. In these instances,
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Surround Sound
Primer – DOC. 6122
