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It's actually a very different idea than the Nazi's weapon. Hypersonic Sound utilizes ultrasonic sound waves to "encode" an incoming sound signal so that it can be reproduced directly in front of the listener. It relies on the "non-linearity principle" of air to cause collisions of ultrasonic sound waves to produce sum and difference frequencies of the colliding waves. Obviously the sum of ultrasonic waves will not even be close to audible frequencies, but the difference waves will be audible and will reproduce the input signal, and it will be extremely directed due to the precision of ultrasonic waves. While this could be used to produce ultra low frequencies such as 6.5Hz, the technology is designed simply to direct sound so that only certain people can hear it. I cannot provide a much more technical explanation, but if you search for Hypersonic Sound, you will find ATC's website with lots of technical docs on the process. Personally, I definitely understand how annoyingly it can be used as an advertising tool and more, but I think it has very novel uses for the field of sound art. Though, this might be just hopefulness coming from a Music Technology student. -Nick On Aug 27, 2004, at 6:15 AM, Suit & Tie Guy wrote: >> Check out this very creepy article about the LRAD............a sonic >> device that can be used as a weapon or as >> a crowd controller. > > yes. it's the same idea that the Nazis were using the 40s. > > they had a parabolic sound cannon which fired a 6.5 hz sine wave at > some obscene dB level that could blow a soldier apart ... if he stood > still for 4 minutes. > > there was a picture of one in the Time-Life book The Secret War, from > their WWII book series. > > they ended up using it for crowd control because getting the enemy to > stand still for several minutes is kind of difficult. > > btw: notice anything particular about that frequency? it's the average > resonant frequency of the human body, which also happens to fall > within the 6-7 hz range which we find most musically pleasing for > vibrato. > > coincidence? > > hopefully at this point a more educated member of this list will chime > in and either provide more significant and thoughtful information or > inform me of my extreme mistaken-ness. either way, if you have more > info on this please chime in, as googling presented me with no > reference pages to include in this post. > --- > Eric Williamson > www.suitandtieguy.com > >