Kockums Tyfon air horn warning system in Sweden

[Daniel]

These horns are normally used instead of sirens in Sweden and Norway. The compressor is self-contained on each horn, and they usually come as single horns or in groups of three (dissonantly tuned a minor 2nd apart).

http://www.youtube.com/watch?v=LwyUMmHdDTA

Manufacturer:
http://www.kockumsonics.com/products/al ... _tyfon.htm

[Corey Hudson]

So you mean its a piston horn? Or does it have a legit compressor piped into a diaphram?

[Daniel]

These are regular diaphragm horns with small compressor units mounted nearby.