The Siren Board

Here are a few antique sirens in Italy.

http://www.youtube.com/watch?v=-DOp0umunJM
http://www.youtube.com/watch?v=HbKNf9x1Jqw
http://www.youtube.com/watch?v=nnWoO-yxBBY
http://www.youtube.com/watch?v=KRZ7oVMcDhQ
http://www.youtube.com/watch?v=kWeKuQZvPoY

Excellent finds! The first siren sounds like a vacuum cleaner. Μaybe the motor rotation is reversed or it's just the camera.

On the first video, I can't figure out what the object beside the motor is. A relay? It opens when the tone goes high and closes when it drops. I wonder if this has a two-speed motor like South American sirens, which alternate between two speeds instead of switching on and off like most sirens.

Daniel wrote:On the first video, I can't figure out what the object beside the motor is. A relay? It opens when the tone goes high and closes when it drops. I wonder if this has a two-speed motor like South American sirens, which alternate between two speeds instead of switching on and off like most sirens.

It's an electromagnet that moves a vertical? damper. That's why the tone drops. Apparently it doesn't block completely the intake or ports.