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Sources of Sound

Author: N.H. Crowhurst

Most sounds are more than a single "pulse" of sound, such as a hand-clap. For example, the reed of a harmonica or accordion vibrates at its resonant frequency and allows the air to be emitted in "bursts." Each burst of air pressure and movement is radiated in the same way as a single hand-clap.

How a reed emits sound

There are also other forms of vibration that produce sound: a vibrating piano string causes the sound board of the piano to vibrate. This moves the air in contact with it, producing alternate waves of compression and expansion (rarefaction). All stringed instruments use the same principle; in the violin, the string vibrations are transmitted to the body of the instrument, which moves the air in contact with it. In addition, there are wind instruments in which a column of air inside a tube vibrates in a manner controlled by the internal dimensions of the instrument. The contact of the air column with outside air at one end of the column or through an opening allows sound to be radiated.

All these sounds are produced by a periodic vibration at regular intervals (definite frequency). Other sounds are not rhythmic, and do not give musical tones because they are due to vibrations that are not regular or periodic - clapping, rattling, and scraping sounds, and all kinds of noises, like those that come from a factory, street, or kitchen, or even voices, except when singing.

How a violin emits sound

Last Update: 2010-11-03