Sirens

[natalie_1982]

Why do the sirens of emergency vehicles have different sounds? Also I've noticed that police cars have several different noises - why is this?

[Ewood27]

To get your attention and indicate when there's more than one of them.

[gazzawazza]

I think it's just whatever the manufacturer puts in (in an effort to make their arrival more noticeable) which may be in response to specifications requested by the services' technical departments.  It's not only police cars, our fire appliances have at least four different tunes

[IndieSinger]

Ewood27 is closer - there are three main sounds emitted from emergency vehicles. If two vehicles are on the way to an emergency, they will both use different sounds. If there are three, they will use one siren each. This is so that you know (without counting) that there is more than one vehicle on its way to try to get past you.

[natalie_1982]

Thanks, but I was thinking that in one street a vehicle may have the "meeeemooorrrrr meeemoooorrrr" (!), then change to "WAWAWAWAWAWAW" and then the "WEEEEEEEEEEEEEWAAAAAAAAAAWWWWWW". Thanks everyone!

[New Forester]

I've always got the impression that Natalie's "WAWAWAWAWAWAW" was a button they hit when some lazy person will not get out of the way.

 

Can what you say really be true, IndieSinger?  Do the different vehicles actually communicate and decide who'll have which siren?  How do they know when there is more than one?  What if there are more vehicles than types of siren?  Evidence please.

 

Personally I find the Wee-ooo-wee-ooo-wee-ooo type confusing.  It slides up and down the scale so much that the Doppler effect is obscured, and you can't tell whether it's coming towards you or away -- unlike the good old Dee dah dee dah.

 

There's another one now with an intermittent sharp hiss of white noise (sorry, can't spell that ...Bchchchch?).  I know it's designed to cut through any other noise, but it only sounds as if the juggernaut behind you has just worked its air-brakes.

 

I think all these new sounds are just councils trying to be trendy.

[natalie_1982]

I agree with NF, when vehicles are on they way to an emergency are they going to call each other to ask which siren they will be using today? Will they argue as hey never get to use the good siren and it's not fair because they always get left with the bchbchbchbch one that noone likes? On discussion in the office, we can't spell that one either or make the noise.

[Hammer]

I have noticed that they generally use the slow woooOOOOOOooooo  woooooOOOOOOoooo but then upgrade to the faster nee-naw-nee-naw when they are approaching a junction or jumping a red light. Maybe the faster version is intended to make us take more notice and get out of the way quicker.

[natalie_1982]

Really though, they ought to make us aware. Someone said it's so you can hear from which direction they're coming as to the different sounds, but surely it'd be safer if you didn't know where they were coming from and just sat still, so to speak, until you'd been passed or were out of the way. If people knew which direction vehicles were coming I bet there'd always be some smartarse who would think that they could just nip across or whatever.

[bluedolphin]

I reamember from a episode of Kojak ...they were speeding to a crime scene at about 5:30 am and Theo told Crocker to switch on the siren.... Crocker asks why....the road was practically empty..... Theo answers....something like " if i am woke up  early so can everyone else be"!!!

[booksworth]

The white noise _is_ to help other drivers spot where the emergency vehicle is. Around here the roads are so clogged with traffic that emergency vehicles usually can't move without the active help of other motorists getting out of the way. I think our local fire engines have only one sounder each: you could always tell which one was on its way.

[TracyJ]

There was some kind of report on Tomorrow's World yonks ago about the horrible white noise being used cos it was the only one proven to be heard over the usual sounds in a car, most prominently, the radio. I live at the back of a police station and am convinced that the sirens dictate which takeaway they're on the way to. The NeeNaw is almost certainly code for 'chicken korma and poppadoms'

[Kev_UK]

It's because some drivers have their music that loud and if listening to techno, etc with it's variety of sounds, the emergency vehicle can be heard without the driver thinking it's part of the song

[gazzawazza]

To Natalie and New Forester, you're absolutely right, we don't talk to each other en-route to incidents and sometimes we don't even know which services are attending so IndieSinger is wrong in his answer. 

I personally use the Waw-Waw-Waw-Waw-Waw one simply because it seems to do the job best and Natalie, I love your idea of us all arguing who's going to use which siren today!!!

[dan_999uk]

Copied from my answer to the other siren post:

There are three main siren tones in use in the UK:

Wail - slow, continuous rising and falling tone
Yelp - fast, continuous rising and falling tone
Hi-Lo - or "two-tones" - alternating high and low pitched tones
There are other tones such as Phaser and Airhorn but these are not as familiar to the public and are seldom used.

The reason for having different tones is because they are more effective in certain conditions - for instance, wail can be heard from a longer distance on high speed roads, yelp is good for getting attention at junctions, traffic lights etc, and hi-lo is good in dense crowds or very slow moving traffic.

Most sirens have an on/off switch and the tone is changed either by a dial on the siren control box or by tapping the vehicle horn. Most sirens have all three of the above tones, some have other things like a public address system.

When I'm going to an emergency, the siren will usually be on wail, and I'll switch it to yelp approaching hazards such as roundabouts, traffic lights etc to get attention and hopefully ease my passage through traffic.

If you have an emergency vehicle behind you and you hear a long horn blast on their normal car horn, it means SHIFT NOW!

To answer specific points above:

• If there's more than one emergency vehicle going through traffic, you use different tones to highlight that there is more than one vehicle present. This isn't agreed but drivers can hear what tones the other vehicle is using and select an alternative.
• Hammer is right when s/he says the tone changes approaching junctions - see above. 
• The "white noise" system that was on Tomorrows World is called "The Localiser" and is made by Sound Alert - unfortunately it didn't really take off any I don't know anywhere that uses it.