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Vehicle Sirens
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Does anyone know the difference between, Fire, Police and Ambulance sirens ?
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They all have what are known as two tones (the na nar na nar) as said. This is known in sonic terms as "The Doppler Effect", sorry I can not put the two dots above the o. This is for long, straight range
At junctions this is changed manually by the driver or co-pillot to a wail, for a wall of sound.
They also have a fast beating siren for in traffic.
The town police cars are fitted with a normally aspirated siren whereas motorway and traffic cars have the optional air siren, much louder for obvious reasons.
Fire and ambulance also have air sirens due to the stopping distant needed for the larger vehicles.
Most of all the emergency vehicles have an air horn as well, operated by a single blast of the normal horn. These are illegal in normal road cars.
At junctions this is changed manually by the driver or co-pillot to a wail, for a wall of sound.
They also have a fast beating siren for in traffic.
The town police cars are fitted with a normally aspirated siren whereas motorway and traffic cars have the optional air siren, much louder for obvious reasons.
Fire and ambulance also have air sirens due to the stopping distant needed for the larger vehicles.
Most of all the emergency vehicles have an air horn as well, operated by a single blast of the normal horn. These are illegal in normal road cars.
Sorry I am thinking doppleganger which has the two dots over the a. Bloody Germans.
Without being too technical, of course the two tones produce a doppler effect. There is of course "two tones" (i.e two seperate pitches, or two seperate wavelengths) in two tones, hence the name. I believe I am right in explaining this for long straight ranges.
Kempie, with respect, you are confusing the issue, but likewise due to my simplification, I know where you are coming from.
Without being too technical, of course the two tones produce a doppler effect. There is of course "two tones" (i.e two seperate pitches, or two seperate wavelengths) in two tones, hence the name. I believe I am right in explaining this for long straight ranges.
Kempie, with respect, you are confusing the issue, but likewise due to my simplification, I know where you are coming from.
The two tones do not in themselves produce a Doppler effect.
If the emergency vehicle is stationary and the observer is also stationary then the siren will produce no apparent Doppler effect; it only occurs where motion is involved.
http://en.wikipedia.org/wiki/Doppler_effect
The Doppler effect can also be heard when a single tone horn passes by.
If the emergency vehicle is stationary and the observer is also stationary then the siren will produce no apparent Doppler effect; it only occurs where motion is involved.
http://en.wikipedia.org/wiki/Doppler_effect
The Doppler effect can also be heard when a single tone horn passes by.
My dear kempie. Yes you are right the two tones do in themselves not cause a doppler effect, in the same way hot water, coffee and a mug does not produce coffee. You need another variable (i.e human application) for the coffee to be made. In the same way you need distance and closing for the Doppler effect.
This is all too technical for me, who has admitted that I do not even know how to put an umlaut above an "O" without cut and pasting.
If you could tell me how to do that in laymans terms, I would be impressed.
This is all too technical for me, who has admitted that I do not even know how to put an umlaut above an "O" without cut and pasting.
If you could tell me how to do that in laymans terms, I would be impressed.
Changing the subject slightly (forgive me Roughquest), why do fire engines have "FIRE ENGINE" written in reverse on the front of them?
Is it in case you see the front of a 6' x 8' bright red vehicle with a 100+ decibel siren and flashing blue lights in your rear view mirror................and your not sure what it is??
Is it in case you see the front of a 6' x 8' bright red vehicle with a 100+ decibel siren and flashing blue lights in your rear view mirror................and your not sure what it is??
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