Is there a science behind the pitch and duration of emergency sirens?

[JoeyM]

I was out having a smoke on the porch just now, when a siren went off in the distance.

At first I didn't know if it were ambulance or police, but it definitely wasn't a fire truck.

I wondered how "the powers that be" decided what siren (speed and duration etc) algorithm should be, for example, police sounds this way and fire truck sounds that way. And what do they use, a perfect sine wave, or something else?

Another thing I have a use for finding out is, what predominant frequencies does a good siren like to put out?


I almost make a disclaimer if my questions are dumb, but really, sirens used on emergency vehicles are some of the most important audio you can broadcast sometimes.

[tenkas]

Well sirens are different from places to places... The police does not sound the same in the US, Canada, France, etc.

Do you have a recording?

[Sk106]

Over here there is.
20 years ago we used to hear these baa-buu-baa-buu ... a constant blairing. But it was noticed that while you clearly heard the sound, even inside your own car, you had great trouble hearing from what direction the sound came from - like if they were behind you, in front of you, or running parallell with you, meaning they might cross your path in the next intersection. Also, when you heard outdoors from a distancem you had no way of telling what direction you heard them from, because of all the echos and reverb.

So they did their homework on that, and now the sirens sound radically different. Here, they alternate in sound character, like going through a cycle of different themes, rotating every 3 second or so. One of those is the same as before, but another of these cycles is a short stabbing sound, kindof like a K-K, K-K, K-K, K-K, which really does help you feel where they are.

When I was a kid, I could clearly distinguish between the ambulance, police or firetrucks - from far away. They all sang the same song, but they had a different kind of timbre to the voice, so to speak. Today, I can't tell the difference at all.

[Jules]

Doppler effect

See halfway down this page..

[The Fresh Man]

Another thing I have a use for finding out is, what predominant frequencies does a good siren like to put out?

They tend to be around 1k or above. I can sometimes sing as high as 1k and can do some pretty good siren impersonations. I sometimes do them to warm up when I'm singing a ballad that needs good falsetto. I also did a police siren guitar solo on one of my metal band's songs. Some people said it was the best solo they had heard because they thought there was a real police car on stage. I got really angry at the lighting guy for not flashing blue and red when i played it but i got that jerk back with the shit in the bag trick on his front door step, though it was his wife who stomped on it and he laughed at her.

[Em Kay]

Originally Posted by Sk106

Over here there is.
20 years ago we used to hear these baa-buu-baa-buu ... a constant blairing. But it was noticed that while you clearly heard the sound, even inside your own car, you had great trouble hearing from what direction the sound came from - like if they were behind you, in front of you, or running parallell with you, meaning they might cross your path in the next intersection. Also, when you heard outdoors from a distancem you had no way of telling what direction you heard them from, because of all the echos and reverb.

So they did their homework on that, and now the sirens sound radically different. Here, they alternate in sound character, like going through a cycle of different themes, rotating every 3 second or so. One of those is the same as before, but another of these cycles is a short stabbing sound, kindof like a K-K, K-K, K-K, K-K, which really does help you feel where they are.

When I was a kid, I could clearly distinguish between the ambulance, police or firetrucks - from far away. They all sang the same song, but they had a different kind of timbre to the voice, so to speak. Today, I can't tell the difference at all.

Yeah, I remember watching a programme about this before they switched to the new sirens (in the UK) for the exact reasons you describe.

[narcoman]

Originally Posted by The Fresh Man

They tend to be around 1k or above. I can sometimes sing as high as 1k and can do some pretty good siren impersonations. I sometimes do them to warm up when I'm singing a ballad that needs good falsetto. I also did a police siren guitar solo on one of my metal band's songs. Some people said it was the best solo they had heard because they thought there was a real police car on stage. I got really angry at the lighting guy for not flashing blue and red when i played it but i got that jerk back with the shit in the bag trick on his front door step, though it was his wife who stomped on it and he laughed at her.

whaaaaaa.?

[Clueless]

This subject is treated in part in the book Soundscapes: The Tuning of the World. 100 years ago sirens were about 85dB, then they increased in loudness by about 10dB every 10-20 years so that by the 1970s we were treated to 122dB wails. The science behind that is simple: HIGH VOLUME IS ASSOCIATED WITH POWER. It's all about acting powerful, regardless of the health and human consequences associated with such expressions of power.

What kind of complete idiot even thought of specifying a 122dB siren, let alone building one?!

[Johnny the Fox]

For the way the human hearing works, a good alarm signal needs to be tonal and intermittent or constantly modulating. That way you get the most attention out of a given sound power.

In many parts of the world the electronic siren signals are more or less imitations of historic signals that were generated mechanically like real rotating sirenes or pneumatic horns. In Europe the loudest sirens are still pneumatic. I think it is the same with firefighters in many parts of the world.

Even today it is not so easy to generate good and reliable siren signals with loudspeakers. The cars need extra batteries, the speakers get hot and can die because of overheating.

Many signals I have heard have a lot of their harmonic energy in the 2k area (the fundamental frequencies are lower). This is probably only partly due to a clever plan but works well because it's a sensitive range of the human ear, even for people with damaged hearing. As well the insulation of normal car windows has a week spot in this frequency range (coincidence frequency).

One thing the European designers deal with these days is the transmission into the car. The Policemen are tired of arriving at the crime scene or accident in an almost deaf state because the signal is too loud inside the police car.

Cheers

[joeydego]

Good question! All I can say is come to NYC. No matter how many sirens, bells, whistles, the word POLICE on every inch of the car, or screaming over the PA is coming out of your car, some jerkoff in a BMW will STILL ignore it all and cut you off. Hours of entertainment. I hate sirens. All of them.

[PinnacleProdUK]

Defo a stoned thought! Lmao!

[Darwin James]

Yea, loud, obnoxious, memorable, and placed high to carry distance.

Kinda like....... (insert an artist name here)

[eascholz]

Nobody mentioned that a bunch of sirens use TRITONES to get people's attention. Oh, so metal

[audiomichael]

Originally Posted by Clueless

This subject is treated in part in the book Soundscapes: The Tuning of the World. 100 years ago sirens were about 85dB, then they increased in loudness by about 10dB every 10-20 years so that by the 1970s we were treated to 122dB wails. The science behind that is simple: HIGH VOLUME IS ASSOCIATED WITH POWER. It's all about acting powerful, regardless of the health and human consequences associated with such expressions of power.

What kind of complete idiot even thought of specifying a 122dB siren, let alone building one?!

Keep in mind that the average ambient noise has probably also gone up at least 10db every 20 years in major metro cities. Add that to the amazing car stereos that most people have (compared to the rotary AM/ FM/ tape decks that people had 20 years ago), and it seems obvious that they would need to increase the siren volume. Next would probably be some kind of emergency BlueTooth-type code that send to cars when they are near an emergengy vehicle.

My dad drove fire trucks for 20 years, and you wouldn't believe how many accidents they almost get into because people don't hear, or don't obey the sirens. It's certainly not some empty display of power.

[tysonviolin]

I saw a rich lady in a lexus SUV (on the phone) almost get clobberred yesterday. She was halfway through the intersection when she realized she was the only one out there and the firetruck went woooosh past her. Only then did she stop...... In the middle of the freakin' intersection. She made me mad watching.

Don't ask HER what the siren sounded like.

[Rikers Beard]

I actually drive rescue/fire trucks all the time on a volunteer dept. As for our dept. we use a shorter faster sweep in town and a longer slower sweep in rural areas. We were always told it is in regard to doppler effect and making an unnatural doppler sound. It also has something to do with the audible range of different frequencies. in rural areas it doesn't make sense to have a high pitched siren since the sounds is absorbed so quickly. Our ambulance just got the latest and greatest that's actually 2 siren tones at once.... no noticeable difference with traffic. In other words if there is a solution they haven't got it yet.
My experience is that volume is a bit irrelevant today as cars are much too soundproof. I've rode many an ass with a siren and airhorn blaring with no luck. However, it's usually a bad deal when they see you finally because they will make a bad choice about where to go often slamming on the brakes at the same time. That being said many times emergency responders are too jacked up on adrenaline to drive defensively anyhow.
The best thing we have is a spotlight on our light bar that make a random pattern to catch rearviewmirrors.

[mikethedrummer]

Originally Posted by eascholz

Nobody mentioned that a bunch of sirens use TRITONES to get people's attention. Oh, so metal

lol \m/

one time back in school there was a siren outside that was clearly audible in the class room and since we were on the topic of audio my teacher stopped the class to listen then announced the specific notes the siren was hitting. =O
he said "you just have to learn to listen"
so apparently "perfect pitch" can be practiced.

[Clueless]

Originally Posted by Rikers Beard

My experience is that volume is a bit irrelevant today as cars are much too soundproof. I've rode many an ass with a siren and airhorn blaring with no luck. However, it's usually a bad deal when they see you finally because they will make a bad choice about where to go often slamming on the brakes at the same time. That being said many times emergency responders are too jacked up on adrenaline to drive defensively anyhow.
The best thing we have is a spotlight on our light bar that make a random pattern to catch rearviewmirrors.

Right...as you say its the wrong tool for the job. In the mean time, the sirens pollute the soundscape of the city, and they damage the hearing of those innocent pedestrians who cannot defend themselves against the racket. Clearly mere escalation of volume levels is the wrong solution--because as the examples go, there is no amount of volume that will attract the attention of somebody determined at all costs to ignore it.

[Dean Roddey]

Actually, my company is working on a high end tube-based siren, which we feel will work much better. It includes a soft clipper to avoid that blaring clipped distortion effect, enhances harmonics in the upper mids, pushes up the air frequencies for a more exciting siren experience, and modulates the lower frequencies for greater apparent separation. And the S/N ratio is far better than the run of the mill sirens most folks use.

You do have to strap four pairs of Barefoot MM27s to the top of your emergency vehicle, and sometimes the 14 tubes in the power amp section can act up if they get wet during firefighting. But we believe that people are willing to deal with the cost and maintenance for a really high quality siren.

[JoeyM]

Originally Posted by PinnacleProdUK

Defo a stoned thought! Lmao!

Thank you all very much, esp Rikers Beard.

The state of world media what it is, I speculate it's inevitable that emergency tones of all kinds will creep their way into advertising and music and everything else. Louder, get their attention is the trend.

There's effects I hear already on Fox News and others where they go to a newsflash and you hear a dialup modem sound halfway in the mix. It's another sound that's hard to ignore.

I might spend some time analyzing the sounds that get our attention, coach's whistles and engines about to tear themselves apart and all that. Why? I don't' know LOL

I just... have... to find out...

[Rikers Beard]

Originally Posted by JoeyM

Thank you all very much, esp Rikers Beard.

The state of world media what it is, I speculate it's inevitable that emergency tones of all kinds will creep their way into advertising and music and everything else. Louder, get their attention is the trend.

There's effects I hear already on Fox News and others where they go to a newsflash and you hear a dialup modem sound halfway in the mix. It's another sound that's hard to ignore.

I might spend some time analyzing the sounds that get our attention, coach's whistles and engines about to tear themselves apart and all that. Why? I don't' know LOL

I just... have... to find out...

Agreed, the media is clearly in tune with what I'd consider subconscious sounds to get our attention. Sounds that we've heard since birth that have a mostly universal appeal/distain. Maybe that's a reason sirens may have less of an effect. Maybe we've become so use to the sounds it doesn't trigger a response like it use to. And hey, volume must work. If anyone wants to think loudness war, I think TV commercials have all Music beat. Is anyone else annoyed when watching TV and the commercial comes along 20db louder? Yeah! Let me scream in your face about boner pills!