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Registered Member #1438
Joined: Sat Apr 12 2008, 12:57AM
Location: Canada
Posts: 218
I've always been a big fan on many different types of sirens and alarms and since the Air Raid Siren is portrayed in our society as domes day I've always wanted one of these. Wanting one of these siren's, I did a slight research about the functions of how they work but never found a website with any types of blueprint or construction tips.
My understanding of these device is that there is a central stator with holes (I wanted to know if any other hole shape then square works.) which is a housing for a fan that creates noise. The air is sucked in through some holes while let out at some holes slightly like a whistle that's pulsing and pulsing at a pretty high rate.
Now, trying to make a Air Raid Siren driven by not any Hemi Engine but an high RPM Motor capable of rotating the fan enough to make and replicate that distinctive noise.
Since this is probably my first time at attempting to try and making anything like, I'm not sure if it's going to be a hard thing to make or easy but some feedbacks would be nice.
(Will not make it any bigger then an averaged sized paper.)
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
You must have found websites about civil defense sirens, such as (with audio clips like , found by googling "siren hemi".
Your understanding is right: in general a mechanical siren is an air blower with mechanical chopper. Flow direction can be axial or radial, openings can be round or rectangular or other. Power conversion efficiency, from prime mover to acoustic output, can be very high.
In case it gives you some ideas for your project: Here is my unfinished ultrasonic siren, idle since 2006. Goal is to generate an acoustic field intense enough to see in a schlieren photograph. RPM is around 50000, as I recall, using a brushless DC model airplane motor. Air source is a vortex blower a.k.a. regenerative blower or ring compressor -- much quieter and with more pressure than a vacuum cleaner.
To mod: if these pics are too big, just ask & I'll resize them to 400 pixels wide.
[edit] So you want to "replicate the distinctive sound" of the civil defense siren, we hope at a much lower power level. The Victory Siren has a rotor with six slots, and spools up to 4400 RPM for a 440 Hz fundamental tone. I think you can do well by starting with a mechanical police/ambulance siren (search ebay for vintage police siren) , or make something similar. Using a speed control to limit the maximum RPM, and the rise/fall rate, can probably make a passable imitation of an air raid warning.
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Air Raid Siren/Civil Defence Siren
The Victory Siren has a rotor with six slots, and spools up to 4400 RPM for a 440 Hz fundamental tone.