Electric Siren for Hire
There are two types of siren (not mouth siren) that are found in the orchestral percussion requirements these days. The first is a manual version that came to prominence in the 1940's and is known as an air raid siren. The second version is similar in design except rather than the power source being manual, this derives from electricity. Both the sirens work on a complicated internal impeller system that draws air through the mechanics of the instrument and creates the unmistakable "whaoouuurrrrrrrwhaoouuurrrrrrrwhaoouuurrrrrrr" sound that is well known today. The German composer Kurt Weill was a champion of the hand cranked siren. Two electric sirens are generally required for Ionisation by Varese.