THE NATURE OF STANDING WAVES
Standing waves may
be created from two waves travelling in opposite directions. Unlike travelling waves,
they do not cause a net transport of energy.
Standing waves can be
generated when plucking a string with fixed ends. Each mode has a wavelength and a corresponding
frequency related to the length of the string.
Membranes with fixed edges also vibrate
in modes. Their natural frequencies are not so simply related.
It is the vibrations transmitted from
the strings to the soundboard together with the air inside the cavity
that mostly contribute to the sound perceived by the listener. Vibration modes of the soundboard can be visualized.
The natural vibrations of the air column in
a pipe (like a flute) are due to standing waves or resonances.
Air-reed instruments like the flute can be seen as a resonator excited
by an air stream which flips in and out of the pipe at the resonant
frequency of the system.
Standing wave phenomena
can also occur in a room at specific frequencies called the resonance
frequencies of the room.