What are standing waves?
Standing waves are the buildup of sound level (increased amplitude) at a
particular frequency that results when traveling sound waves coming from
opposite directions constructively combine to increase amplitude above
that of the original waves. Standing waves occur when sound is reflected
back toward the source at the original frequency. This is why it is
important that soundproofing materials actually absorb the sound (by
converting the energy they contain into heat) and not simply try to block
it from coming through a wall. The number of times and the
efficiency with which a sound wave is reflected will determine how high
the amplitude will rise. In all cases it will be louder than the
original sound produced. The
amplified sound you hear in a sea shell occurs because standing waves are
formed as the interior of the shell reflects back the noise of the blood
rushing through your ear.
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