The Siren Board

That mystery siren almost looks like a single head HOR to me, maybe rotational?

Hedberg had sirens in several shapes, and E.D. Bullard had conical-rotor sirens in this shape. However, if you compare it with the size of the windows below it, the siren isn't that big.

Daniel wrote:Hedberg had sirens in several shapes, and E.D. Bullard had conical-rotor sirens in this shape. However, if you compare it with the size of the windows below it, the siren isn't that big.

Now that I look at it, it does seem to resemble the shape of an E. D. Bullard siren, just with one head. Here is a picture of some:

A bit off topic, but in the siren in the very front, does it seem to have a coding mechanism?

Yeah, now that I look at it again, it looks nothing like a HOR. I just thought maybe it was at an odd angle.

Yes, the one up front has a coding system. It's a solenoid operated sleeve over the stator that rotates to close the ports.

Most of these were used in San Francisco. With six ports, these should sound almost exactly like those damper-equipped sirens in Japan. It's no wonder that these were replaced with STL-10's in the 50's.

Looking at past years arial photography, neither Thunderbolts in Sacramento have rotated since roughly 2009. Not sure if the system is totally decommissioned, or if they just aren't tested anymore. Either way it's a shame.