Who decided on the sound that sirens (police, fire, ambulance) make?

September 17, 2005 7:49 PM

Who decided on the sound that sirens (police, fire, ambulance) make?

I've always wondered how the "siren sound" in fire trucks, police cars, ambulances, etc. was agreed upon and why it differs in other countries. Is there a reason it is the way that it is...maybe so sound can travel?

posted by greenbean to technology (10 comments total)

Well, it probably initially had something to do with the physical construction of a Siren. The little rotating wheel inside the device was spun up by a hand crank, so it would initially start out low until the person had spun it up to a given speed. When the person stopped spinning the crank, the internal wheel would slowly spin down... thus the pitch would also slowly lower.

Then the person would repeat. Then the electronic ones were made, which used oscillators to mimic the old style.
posted by odinsdream at 8:25 PM on September 17, 2005

Even though the sound is different in certain countries, the mechanics of the siren sound are designed to use the Doppler effect to assist pedestrians/drivers determine how far an emergency vehicle is, and from what direction it is approaching.
posted by purephase at 8:38 PM on September 17, 2005

I read a totally fantastic article a couple of years ago -- I'll be damned if I can tell you where -- about how research has been done that came up with a much more effective siren. It was designed so that others can determine its location, avoiding the problem with standard sirens of having no idea of whether you need to pull over or if it's two blocks away. The problem with this weird beepy new siren was that firefighters hadn't been conditioned to get all charged up by it. They'd get to the fire without any adrenaline. So nobody liked it, and it was scrapped.

No source. I suck.
posted by waldo at 9:07 PM on September 17, 2005

Waldo, was it the directional sound siren research from Leeds University and Sound Alert?
posted by acoutu at 9:28 PM on September 17, 2005

purephase writes "the mechanics of the siren sound are designed to use the Doppler effect to assist pedestrians/drivers determine how far an emergency vehicle is, and from what direction it is approaching."

The doppler effect doesn't aid the recognition of direction or distance and is not unique to sirens - any moving sound source (relative to the listener) will exhibit the effect.

The broadband/white-noise burst sound signals which are still being trialled in various countries are designed to aid other road users pin-point the location of the sound source, but intermittently injecting a burst of broadband "static" in the sirens' output - it is much easier for our brains to identify the direction of broadband noise than it is the much narrower standard siren sound.
posted by benzo8 at 10:32 PM on September 17, 2005

I remember reading about the white noise directional sound siren acoutu mentions when the British news presenter Sheena McDonald was run over by a police car in central London back in '99.
posted by forallmankind at 12:23 AM on September 18, 2005

The changing pitch of a siren helps it to be heard above other sounds, whatever sound a listener happens to have closer. I've often wondered if the two-tone European sirens are easier to hear than the ocilating American sort. I'm entirely unsure about that.

Its definitly the case that the more a siren varies, the more likely it will be noticed, especially considering the sound systems folks have in cars these days.
posted by Goofyy at 3:11 AM on September 18, 2005

Not an answer, but I read somewhere that Germany recently changed (or will soon change) their police sirens from what they were before to the American style sirens.
No idea why.
posted by easternblot at 8:46 AM on September 18, 2005

I always heard that the European style tri-tone siren came about to replace the familar American style siren due to the latter's similarity to air raid sirens and a post WWII populace all too familiar with air raids. Probably BS but you never know.
posted by spartacusroosevelt at 10:40 AM on September 18, 2005

A bit of a tangent, but the opening notes of The Beatles' "I Am The Walrus" is meant to emulate the sound of a police siren. (#5)
posted by Ian A.T. at 3:51 PM on September 18, 2005