Whistle

A Whistle is a noise-making device which produces sound from a stream of forced air. Many types exist, from small police whistles, to much larger steam whistles used on locomotives and ships. They are not usually considered a musical instrument, but musical versions that work on the same principle exist, for example the tin whistle, organ pipes and the Recorder.

The whistle works by causing the smooth flow of air to be split by a narrow blade, sometimes called a 'fipple', creating a turbulent vortex which causes the air to vibrate. By attaching a resonant chamber to the basic whistle, it may be tuned to a particular note and made louder. The length of the chamber typically defines the resonant frequency. A whistle may also contain a small light ball, usually called the pea, which rattles around inside, creating a chaotic vibrato effect that intensifies the sound.

A steam whistle works the same way, but using steam as a source of pressure - such whistles may produce extremely high sound intensities.

Many people are able to whistle, that is, to produce sound by forcing air through their lips which are shaped to create the required turbulence and a resonant chamber (the mouth). A more intense whistle may be created using the fingers to shape the opening - this allows the mouth to relax permitting a much more forceful stream to be blown through. This type of whistle is usually called a wolf-whistle.