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Let
us have a look at the principles involved in the formation of
sound. They may be defined as follows:
Curve
representing a 3 Hz frequency.
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The period expresses the distance between two crests of a
wave thus determining the pitch of the sound perceived.
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The frequency represents the number of oscillations per second,
generally expressed in hertz (Hz). The higher the frequency,
the sharper the sound. The human ear perceives those sounds
whose frequency lies between the infrasounds (< 20 Hz) and
the ultrasounds (> 20 kHz); the latter is reduced with age.
Only certain animals, such as bats, are sensitive to ultrasounds.
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The amplitude determines the power of the sound. It is the
maximum elongation of the sound wave. The greater the amplitude,
the louder the sound.
It
should be noted that the amplitude of the vibration decreases
with the distance, for the energy of the wave is distributed
in an increasing volume. It should also be noted that when a
wave is canalised in a cylindrical tube (as in the flute) or
by a reflector (such as the belly of the violin) the amplitude
is scarcely diminished. This explains why we can hear sound
in a tunnel or in a subway station so well. It is the principle
used by the violin to amplify the sound and direct it to the
listeners!
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