is the compression and rarefaction of sound waves
traveling through air. Sources of sound compress
(squeeze) air molecules, which then rarefact
(expand). The rarefaction compresses adjoining
molecules, which rarefact-compress adjacent
molecules. The cycle continues until it terminates
in the ear or fades into the atmosphere. It is the
cycle of sound.
Hertz (Hz) = cycles per second.
One thousand = one Kilo or K
meg, or M = one million
KHz = one thousand Hertz
= one million Hertz
Lines on an
engineers translate sound into measurable illuminated
lines on the screen of an oscilloscope. The
o-scope modulating lines illustrate the wavelength,
amplitude, and frequency of a sound wave.
oscilloscope reveals a ten-octave frequency range of
sound that spans from 20Hz to 20KHz. The area of
20Hz to about 500Hz covers bass and rhythm
frequencies. The core of the human voice and
instruments occupies the region of approximately 500Hz
to 2KHz. The balance generates vocal detail
and ringing-reverberating sound.
The speed of sound = 1130 ft/second
may compute the wavelength of sound by dividing
the speed of sound by the frequency. For example,
20Hz has a wavelength of 56.5 feet or 1130 ÷ 20, while
20KHz has a wavelength of about 0.0565 of an inch or
1130 ÷ 20K.
amplitude or objective volume
measurement of sound is the decibel (db), a logarithmic
unit of sound pressure. It is a scale that extends
from 0db to 194db. Sound
engineers employ a logarithmic scale because of the
immense range of human ear. It spans from the
threshold of hearing to beyond the level of pain.
The threshold of hearing is the level created by a
molecule of air landing on the surface of the
eardrum. You read that right. The pain
threshold is at about the sound pressure level of a
large aircraft during takeoff at close range -- 120db.
the 1930s, Bell Labs researchers Fletcher and Munson
observed that the subjective response of the
human ear differed from the objective measurement of
sound pressure level. They determined that the
human ear is most sensitive to the range of 1KHz to
Frequencies above and below must be increased in volume
to perceive as equal volume. The effect becomes
more prominent as the volume decreases. The effect
diminishes as volume increases. Fletcher and
Munson defined this subjective or psycho-acoustical
response to sound as loudness.
A doubling of loudness =
about 9 to 10 db change in sound pressure
doubling of amplified power =
an increase of about 3db.
Speed of sound =
1130ft/second at seal level.
Frequency range of audible sound =
20Hz to 20KHz.
Range of audible wavelengths =
56.5 ft. to 0.0565 in.
Threshold of hearing = 0db
Threshold of pain = 120db
can also travel through other media such as water, wood,
steel, etc., but
sound cannot travel through a vacuum such as the vacuum
of outer space.
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