Article 04 August/September 2006

Mechanical Sirens

Electronic sirens found on emergency vehicles today first appeared in the 1960s. Before this, emergency vehicles were equipped with a mechanical siren consisting of a motor that spun an air impeller.

In this photo taken in 1960, Associated Ambulance manager Gerry Price is shown leaning on a massive Federal 'Q' Series mechanical siren. Associated was one of the private ambulance services operating in the City of Calgary in the early 1960s.

Mechanical sirens were often referred to as coaster sirens or growler sirens due to their characteristic low growl when only partially "revved up." The driver controlled the volume and pattern of the siren with a dimmer switch mounted close to the driver's left foot.

Mechanical sirens were available in a variety of sizes and the sound they emitted was proportionate to their size - a small siren would have a cheap sounding high pitch whereas a large siren would start off with a low pitch and progress to a higher volume. Large sirens drew an enormous amount of electrical amps from the vehicle's alternator and battery - so much in fact if the driver wound up the siren too aggressively, the vehicle's headlights would dim and the sparkplugs would retard, resulting in the vehicle's engine running rough and causing the vehicle to lurch forward. A large mechanical siren could draw as much as 350 amps at peak, whereas today's electronic sirens only draw 20 amps.

Another disadvantage of mechanical sirens was their inability to operate in an instant on/off fashion. At start up it could take a block or two of driving before the siren reached full volume and when you arrived at your destination the siren would still be wailing away unless your siren was also equipped with a siren brake.

Copyright 2006 Peter Adsten