Vehicle Sirens

[Roughquest]

Does anyone know the difference between, Fire, Police and Ambulance sirens ?

[Octavius]

Yes.

Wee wa wee wa
Nur nur nur nur

and

parp, wuuuurp, parp , wuuurp

[Roughquest]

Waaaagh ! Octavious that is just soooo funny, made my afternoon - excellent - now I can tell which is which...LOL

x

[redcrx]

nope. I always called them nee naw lorries (fire), nee naw Vans (ambulances) and nee naw cars (police)

Get confused now the fire brigade have cars and the police have vans.

[Octavius]

I believe they differ between the various UK authorities.

[liquidspace]

This question has made everyone sound like 5 year olds lol.

[Joe_the_Lion]

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.

[sleepyj]

do they hear the siren really clear in the vihicle ? if they do you would think they would end up deaf . any one know

[Joe_the_Lion]

No sound is energy and the energy of such is going away from the car. You can hear it of course, but it is quieter in the emergency vehicle than it is for other road users.

[kempie]

The Doppler Effect (no umlaut over the 'o') is the change of frequency perceived by an observer moving relative to the source of a sound wave. This is not what produces the "two tones" of the siren but is why the sound of the siren changes when an emergency vehicle passes by.

[Joe_the_Lion]

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.

[kempie]

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.

[Joe_the_Lion]

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.

[kempie]

Hold down the Alt key and using the number keypad (with Num Lock on) type 0246.
�

Alternatively, type an 'e' after the 'o'
oe

e.g. M�hne, Moehne

[unruliejulie]

they all sound the same to me Roughqurest, i like the drivers and passengers of the fire engines the best though!!!!!!! :-)

[fly258]

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??

[Joe_the_Lion]

Because the police have large vans aswell and in night time red would be obselete. You don't have to pull over for a fire engine do you?

[Roughquest]

so you can read them in your rear view mirror the right way as to read 'FIRE ENGINE' or 'AMBULANCE'