Air raid sirens have an important job to do, and have been a critical piece of public safety infrastructure in times of geopolitical turmoil. They sound quite unlike anything else, by virtue of their mechanical method of generating an extremely loud sound output. They’re actually remarkably simple to build yourself, as [MarkMakies] demonstrates.
[Mark’s] build relies almost entirely on 3D printed components and ex-RC gear. The sound itself is generated by a rotor which spins inside a stator. Each is designed with special slots, such that as the rotor turns at speed, it creates spikes of air pressure that generate a loud wail. The rotor and stator are fitted inside a housing with a horn for output, which helps direct and amplify the sound further.
To spin the rotor, [Mark] used a powerful brushless motor controlled by a common hobby speed controller. The actual speed is determined by a potentiometer, which generates pulses to command the speed controller via a simple 555 circuit. By ramping the speed of the motor up and down, it’s possible to vary the pitch of the siren as is often done with real air raid sirens. This action could be entirely automated if so desired.
If you do decide to build such a siren, just be wary about how you use it. There’s no need to go around agitating the townsfolk absent an actual air raid. It’s worth noting that sirens of this type aren’t just used for air raids, either. They’re often used for tornado warnings, too, such as in Dallas, for example. But why not for music?
I’ve always wanted an air raid siren, ideally mounted outside my house and wired to my home security system on a 3 minute delay (so I can still cancel it in case of a false alarm, before the entire neighborhood has to hear it, and I likely end up with a several hundred dollar fine from my HOA).
It’s just such a classic sound, that drives an instinctive reaction that a bad situation is brewing.
Just keep the siren out of sight, and “play dumb”/act surprised and confused if/when any complaints are made. Providing evidence or proof of a temporary sound’s location is a lot more difficult than say proving an object’s location (simple photograph).
How about you just act like an adult and realize you can’t always have your noisemakers?
I’m going to take one of those to the local rc airplane park… :D btw.. i feel like i have seen this post before?
I knew a guy who bought an old air-raid siren off ebay and restored it and cranked it up. Earned him a visit from the authorities.
I help restore an old one from the 1940’s, and it worked excellent. Very loud, about the same size as the one in the article.