Grumman/Northrup developed an electrohydraulic driven poppet valve
device, known as a HIANG or High Intensity Acoustical Noise Generator
which could modulate a moderate pressure air stream and generate an
iterated shockwave or pulse train at very near the theoretical upper
limit of 194 dB at the throat of a horn. NASA used these to stress test certain spacecraft components during the 1970s.
In addition to HIANGs, modulated air loudspeakers, such as Wyle Laboratory's WAS-3000 are also used. The WAS-3000 operates very much like a voice coil driven diaphone in that instead of driving a cone or dome as in a conventional loudspeaker driver, the voice coil drives a slotted cylinder positioned inside of stationary slots in which compressed air at about 30 PSI flows at a high rate. When audio current flows through the voice coil, the air flow is modulated as audio at up to 30 kW acoustical. That's not amplifier watts, but actual acoustical watts!
The Army Research Lab also uses one of these to drive the giant truck mounted horn of their MOAS (mother of all loudspeakers) to simulate battlefield ordnance sounds during battlefield training. You have to see this thing to believe it!! It's as big as the long flatbed truck that it is mounted on!
SirenMadness wrote:The Diaphone is basically a siren with a reciprocating chopper, and a diaphragm as the "motor." Speaking of Diaphones, does anyone remember that monster they used on rocket-launching sites to test for large acoustic effects?