For the "Steam Whistle" beer brand, see Steam Whistle Brewing

A steam whistle is a device used to produce sound with the aid of live steam. The whistle consists of the following main parts, as seen on the drawing: The whistle bell (1), the steam orifice (2) and the valve (9).

When the lever (10) is pulled, the valve opens and lets the steam escape through the orifice. The steam will alternately compress and rarefy in the bell, causing the sound. The pitch, or tone, is dependent of the length of the bell.

Uses of steam whistles

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Steam whistles are often used in factories, and similar places to signal the start or end of a shift, etc., as well as on trains for signalling. Steam whistles on trains have a long history.

Train whistles originated around 1832 by way of a musical instrument designer who made them for signalling purposes. They typically consist of three, four, or five whistles that sound together. Typically train whistles form a minor seventh chord.

An array of steam whistles arranged to play music is referred to as a calliope.

Recently the steam in whistles in trains as well as in calliopes has been replaced with compressed air.

Recent developments to the steam whistle include toroidal whistles, which behave as large virtual phased arrays of about 30 traditional steam whistles within a single toroidal chamber. This arrangement insures that the entire virtual array radiates in phase and adds to the output. Toroidal whistles are represented by the following patents:

U.S. Patent 4429656, Feb 7, 1984 Toroidal Shaped Closed Chamber Whistle

U.S. Patent 4686928, Aug 18, 1987 Toroidal Whistle

These whistles achieve outputs as high as 125-135 dB at 30 meters at a pressure of only 15 PSIG, making them comparable in both efficiency and output to the loudest warning sirens.

See also

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Train whistle

Sound production | Aerophones