# air raid siren

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#### TheMG

I just got this crazy idea...

Everyone knows the characteristic sound of a two-tone air raid siren right? For those who don't know what I'm talking about: http://youtube.com/watch?v=S3Z91xfFZ1U

Ok, so here's the idea: building some type of circuit to emulate that sound.

From my research so far I've found out the two tones are at a 5/6 pitch ratio, and go up to about 500Hz on full speed.

So the circuit would have to produce these two tones, maintaining the same ratio all the while the frequency and amplitude goes down and back up according to what I think would be a triangle wave (simulating the spinning up and down of the motor).

I don't know yet, but I think a little distortion would be welcomed for a more "realistic" sound.

If I/we succeed, that should make for a kick*** alarm clock, doorbell, whatever other use you might think of!

Ok go!

#### eStatic

TheMG said:
If I/we succeed, that should make for a kick*** alarm clock, doorbell, whatever other use you might think of!
Ok go!

Right! A sound to remind you that your fellow man is likely to blow you and your loved ones to burning hell. I love it. Maybe you could have screams of agony from women and children segued in after the siren dies down. That would really be kick*** eh?

Don’t' mind me, I've just got this problem where I have an immediate puke response to the smell of burning flesh.

#### Don Bunce

A 555 timer chip would be a good place to start.Two of them tuned to a 5/6 ratio,and another one used to vary the freq.Not sure how well they would track,but might make interesting sound as they go in and out of tune,especially at 110-120 db.

Another way would be to make a master osc,and divide the output by 10 and 12 to get the two tones.If you want to get fancy,you could add an additional LFO (1/20 hz) to simulate the doppler shift of a rotating siren.

If you are not already familiar with it,do a Google search for the Big Red Chrysler air raid siren.(victorysiren.com)Also search 555 timer,and siren circuits.

#### Pano

Paid Member
Not something I would want to do.

We have Tsunami warning sirens here in Hawaii. Similar sound.

They test them the first weekday of every month.
So your circuit would have me running for high ground, or running to take my landlord the rent check!

#### TheMG

Lol, I don't know, but for some reason I like the sound. Again, don't ask me why.

Fact: I've never heard such a siren in real life, and to the best of my knowledge there are no such sirens installed/used over here.

I don't know if I'll ever actually attempt this project now that I think about it. Haven't got the time currently. Don't even ask where the idea came from.

#### Don Bunce

You need to experience one of these in "person" to get the full effect,not only are they insanely loud,they vibrate your entire body.

As "cool" as they may be,(along with truck,train,and boat horns,steam whistles,etc)they are not toys,and besides the serious hearing damage potential,your neighbors and the local law will not be amused,since they warn of impending disaster.

Anyway,an electronic version that can be kept to a reasonable volume seems to be a sensible project.

Or you can get an aoogha horn on Ebay for about \$40.00

Let's see you sleep through that!

#### TheMG

Yeah, that was part of the electronic idea. Very difficult to make a small scale (read: much less loud) siren such as this while staying true to the sound of the real thing. An electronic version, assuming the sound produced can be made to resemble the real thing, can be adjusted as loud or as silent as needed.

#### OzMikeH

On occasion I need to work on equipment in close proximity to those sirens which may go off ay any time. The spec sheet says they produce 153 dB. I have no idea what the distance that level is measured at.
When we go near them if they are not isolated we have to wear ear plugs and ear muffs. They will not protect my hearing, but they will reduce the level enough so you can run away from the siren before going deaf. You have to stick your fingers in your ears 200m away.
I've never experienced one going off, I imagine it would shake the snot out of your nose.

I suggest you get a sound recorder/player chip. I used to use them for automated voice prompts for radio controlled runway lighting. Very easy to use.

I think your doorbell should play the sound of someone knocking on the door....

#### Pano

Paid Member
OzMikeH said:
I think your doorbell should play the sound of someone knocking on the door....

He-he... My mobile phone rings like a good old telephone bell. That's the retro spirit! (I like the knocking doorbell even better)

#### unclejed613

i once made the sound on an EMC (analog) synthesizer in high school. i used square waves and two VCO's running off of a common control voltage and added a bit of tape echo with a 500mS delay to get it to sound just right. the sound should maintain the 5/6 ratio, as the real siren uses a spinning cylinder with two separate sets of slots in it (the slots are the reason i chose square waves, and the sets of slots are on the same cylinder,and that's the reason for maintaining the ratio). you may want to simulate the spinup and spindown sequences as well. since (at least here in Colorado) the horns on these sirens rotate, you may want to add a 20% depth tremolo with a rate of about 0.3hz. in other parts of the country, such as Massachusetts the slow tremolo doesn't exist, since the raw siren is mounted on telephone poles

#### cyclotronguy

The real air raid siren

Old ones were powered by big and I mean big Hemi V-8 power plants. You don't know loud till you hear one of those up close and personal.

Up close and personal being anywhere close enough to hear.

Cyclotornguy

#### unclejed613

the ones i remember back east in Boston were big yellow or red cylinders with 3 cone shaped vents at the top. they were usually mounted on telephone poles or the tops of buildings. kinda looked like the following picture:

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#### cyclotronguy

What I had in mind produced 138 dB at 100 feet as it slowly rotated on it's turntable. Exit velocity of air at the horn was 400 MPH. Photo from an old advertisement. Clearly heard at 4 miles

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#### form109

id rather make a Mechanical one with a Blower and some Stators..

#### form109

the ones i remember back east in Boston were big yellow or red cylinders with 3 cone shaped vents at the top. they were usually mounted on telephone poles or the tops of buildings. kinda looked like the following picture:

http://www.vistafd.org/images/siren-f.jpg

Sort of Like This one?

#### Steerpike

That's exactly what I need to direct at my doofus neighbour!

#### unclejed613

exactly.... VERY LOUD!!!! you wouldn't want to be standing where the pic was taken from if it went off.... you would quickly find out what the "threshold of pain" and "threshold of feeling" in the Fletcher-Munson curves is referring to.

#### form109

exactly.... VERY LOUD!!!! you wouldn't want to be standing where the pic was taken from if it went off.... you would quickly find out what the "threshold of pain" and "threshold of feeling" in the Fletcher-Munson curves is referring to.

Most Warning Sirens are Between 102 and 135 Decibels...when Measured at 100 Feet.

The Largest Directional Siren (Rotating) is an ASC Tempest 135 Which is Rated 135 Decibels at 100 Feet

The Largest Omidirectional Siren (Non Rotating) is a Sentry 40V2T Which is Rated 130 Decibels at 100 Feet.

#### unclejed613

out here in colorado, they're used for tornado warnings now, and recently i've heard an electronic version that sounds like a modern police siren except the warble is set at a fixed rate that remains the same for the whole 5 minutes or so that they run the siren instead of the changing warble modes that emergency vehicles use.

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