The Siren Board

This is a Mussolini-era electromagnetic siren from La Sonora. It is essentially a huge electric horn suspended above a conical reflector. Rome had a system of these during WWII and a few still remain. I posted a video of one of these being used by a VFD as a fire horn (second video), but today I found one (first video) where the horn's pitch is being modulated to imitate a siren. The third video is a news article which shows several of these horns plus a view of the control box.

Variable tone


https://www.youtube.com/watch?v=NU6QD1g3oGc


Straight tone


https://www.youtube.com/watch?v=Jx0MJNB2lzE

News article


https://www.youtube.com/watch?v=NDrNqgPoygs

Very cool! I remember seeing a bunch of these on old Corbis images years ago. Now we know what they sound like!

That's an interesting type of siren.

Very interesting. I wonder how this modulation effect can be generated with an electromagnetic horn. Certainly not by reducing the voltage, that would make the horn to be more quiet. Maybe with a frequency converter? Also I wonder if this effect was originally used as a signal.

I know this is a little off topic but Marshal H is that you?

I'd always presumed it was a vibratory horn that could be either frequency-modulated or mechanically adjusted (one switch was marked motor). Perhaps it is more of a speaker coil. The three-horn version looks a lot like that mystery siren in Montana.