Everyone knows what a siren is, or at least what it does, but not everyone knows how a siren works. While most fire engine sirens these days are electronic, the traditional siren is a type of mechanical air-gating system, converting a steady air stream into a rapid series of pulses that we hear as a tone. It’s possible to make a siren that is not as loud as a warning siren, but that produces controllable, steady pitches and can be used to play melodies. This picture shows one such musical siren.
Sounds of the Musical Siren
Musical siren construction is covered in the aerophones chapter of the book Musical Instrument Design by Bart Hopkin (one of many, many topics covered in the book). In addition, more extensive information on sirens appeared in two articles appearing in the Experimental Musical Instruments quarterly journal. The first, in Volume 12 #4 (June 1997) covered the history of sirens, with explanations of basic principles and lots of wonderful historic engravings of early instruments. The second, in Volume 13 #1 (Sept 1997) had information on musical siren construction.