The Siren Board

We acquired a fiberglas horn from the guys in Michigan and a local sheet metal shop made a spiral ductwork elbow work. Two 12" bolt flanges from Graingers connect the horn to the elbow. We' are going to paint this new stuff with Army green and an artist friend says that she can age it to match. That's my volunteer standing there.



I'll soon post a video of it spinning while an actual recording of a siren starting up and slowly shutting down in one revolution.

An acquaintance in Ohio has an original metal horn. He sent me the measurements and I compared them with the fiberglas horn and they were all but identical. We'd love to get the engine shroud if anyone knows where one is lurking.

what speed does the motor spin at?

The motor is 1725 rpm. If you are referring to the whole unit, it takes about one minute to make one complete revolution.

oh, so not that fast then. it should make a good display!

The recording of an 8-Port Mobil Directo is exist, but IIRC the only one is the one at Milwaukee, WI, a gas-powered variant which turned electric.

Anyhow, Dennis,

1. Assuming there's no Gas MD recording around, could we see a video of your museum unit running from start, engine running, signal then shutdown? Not rotating is the another thing. (Talking about rotating, the siren supposed to turn using only one engine / motor)

2. Instead of playing a recording through the horn, why not have the siren really sound using its chopper (The part you refer as "... cylinder spinning in another hollow cylinder with holes parallel to each other to create sound...")? That'll make more sense to visitors. Noise levels? A full demonstration outdoors and/or stuffing the air intake (Lower horn), projector horn (Upper horn) (But put fabric BEFORE the smaller end) and elbow with layers of black colour fabric could do it. Some Thunderbolt 1000(T and 1003) owners stuff the horn to minimize sound output during test runs.

Great to see this siren being restored!

I would love to see a full power run of this siren.

This is the post I have been waiting for for years. Great to see that more progress has been made on it. Was it originally designed to spin at 1725 RPM? That would make it an octave lower and considerably quieter.

Zarlog wrote: ↑

Sun Oct 28, 2018 7:37 pm

This is the post I have been waiting for for years. Great to see that more progress has been made on it. Was it originally designed to spin at 1725 RPM? That would make it an octave lower and considerably quieter.

In this instance, the motor only drives the rotation mechanism, not the chopper - that’s driven by the “gasoline” engine. The engine should run at around ~3500 rpm, if I recall correctly