The Siren Board

Your best bet is probably a compressed air system with air horn. When the alarm is triggered, the small air solenoid releases letting air from the tank flow into the horn and sound the horn. This requires almost no power to operate, but would require someone to go out there every time the horn sounds to refill the tank. There would also not be an easy way to test since again, someone would have to physically go out there to fill up the tank. But it really is the most simple and cost effective way to provide a short but very loud warning. I would worry about electronic speakers failing shortly in an environment like that, plus there more that can go wrong in that type of system.

If it were a Tyfon-type diaphragm horn, it would need a water-tight, corrosion-resistant diaphragm, horn, and housing. On the other hand, whistle buoys have used a type of steam whistle for over a hundred years. Since they are brass and have a simple design, they can get filled with water and blown clean repeatedly. They actually found the three-bell whistle from the Titanic on the ocean floor, cleaned it up, and it still blows. Perhaps a toroidal whistle operating on compressed air or CO2 would make an efficient alert, because the toroidal design can generate as much sound output as a large siren.

Hey all, I just wanted to say thanks for the help you gave me.

I just came out of our client meeting and my lecturer loved the concept and selected it out of five others for further development and production of a working prototype model.

Congratulations on having your design selected. What will you do to assure that the horn is pointing toward the intended warning area when it sounds?

I was under the impression the sound would be emitted in a relatively uniform manner.
I'll have a look into the design further.

Johnoe wrote:I was under the impression the sound would be emitted in a relatively uniform manner.
I'll have a look into the design further.

I'm no acoustics expert but have learned a thing or two over the years.

Generally sound will radiate uniformly from a source but the catch is that it won't be as loud as focused sound. It's pretty much the same principle of a light globe versus a laser pointer. If you focus the sound waves to a specific area, they will be much louder than omnidirectional emitted sound.

I've noticed that your design only has one sound emission point. You might want to consider the hole being covered completely if the device were to "land" in such a way on the sea bed. Multiple ports should aid this (i.e. a port at each of the compass points (if that makes any sense)).

You could also look at a recessed exponential horn to aid in sound focusing. It looks like the holes depicted in your design won't be sufficient in achieving the maximum possible output (something to do with frequency cut-off (I get lost at this point)).

Hope that helps.

:: Edit ::
This is what I mean by recessed horns and that they should be at "compass points" (on all four sides): http://www.jmarcoz.com/sirens/kassel4_ge.jpg

This siren is the German HLS, also driven by compressed air.

Great, thanks, that is a big help.

One design might involve placing the horn on top of the buoy with a cone-shaped omnidirectional radiator suspended above the horn opening. This will direct sound in all directions as long as the buoy is upright.

Or just space four horns around the buoy.