In its most simple form the siren consists of two metal disks, each perforated with equally spaced concentric holes. One disk forms the top of the "wind chest" while the other rotates close to the first. Air is forced through the system, which causes the upper disk to rotate, owing to the slanted bore of the holes. As the disk rotates the flow of air is periodically cut off and reinstated resulting in a regular emission of puffs of air. The ensuing fluctuations in air pressure set up simple sound waves of a specific frequency depending on the speed of rotation of the upper disk. De la Tour arranged for the upper disk to drive a mechanism that can count how many revolutions per second were produced. Knowing how many holes there are in the disks, and thus how many puffs of air per rotation, one can immediately calculate the exact frequency of the sound produced.
The use of the siren in experiments rapidly became widespread. Prior to its invention, scientist had no reliable way to measure or create tones of specific frequency so for acousticians the siren was a great step forward. De La Tour's original design was rapidly improved upon and developed for new and ingenious uses by the great German scientist Herman von Helmholtz (1821-1894) as well as the famed Parisian acoustic instrument maker Rudolph Koenig (1832-1901).
