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[danickstr]

I saw an evening news show where a guy had discovered hot to use two ultra-sonic frequencies to create a beat tone in the audible range, and you only had to "shine " both frequencies on someone for them to hear it quite vividly and the person next to them (lets say , in bed and trying to sleep while you are watching TV) hears nothing.  it was a TRULY amazing phenomenon.  And then it vanished from thin air and I never read a thing about it again.

I am telling you it was the coolest thing, to have silence in one area and the phase difference focused on the microphone suddenly getting really loud as it passed into the band area, and then silent again.


anyone know anything about this?  if I disappear after this post, I will know why.  what a governmental coo it would be to have this technology(and I am sure they do), and probably just don;t want us schmoes to have it for shutting up sleepy girlfriends/wives.

[dcollins]

danickstr wrote on Mon, 18 July 2005 17:46

I am telling you it was the coolest thing, to have silence in one area and the phase difference focused on the microphone suddenly getting really loud as it passed into the band area, and then silent again.

By the time you get the SPL high enough for air non-linearity, this might also qualify as a non-lethal weapon!

More for crowd control than "each person gets their own mix."

DC

[rollmottle]

http://www.holosonics.com/technology.html

[Ronny]

dcollins wrote on Mon, 18 July 2005 22:18

danickstr wrote on Mon, 18 July 2005 17:46 I am telling you it was the coolest thing, to have silence in one area and the phase difference focused on the microphone suddenly getting really loud as it passed into the band area, and then silent again. By the time you get the SPL high enough for air non-linearity, this might also qualify as a non-lethal weapon! More for crowd control than "each person gets their own mix." DC

No doubt the military implications, but this is nothing newer than placing the receiver at Arrecibo in the correct spot to maximize the parabolic gain from the 1/4 mile wide dish. The same physics apply, the exception is that line of site distance on the Earth would allow a much smaller transmission bandwidth. This technology is not baffling nor new. I'm a bit confused, however, on how ultrasonic frequencies can make audible freq's bypass anyone that is within the sound tunnel going to the intended recipient. I'm not so sure the technology has arrived at beaming around corners or through solid objects. All I see is groundwork that the military did 30 years ago.

[danickstr]

ronny

i apparently did not adequately describe the gist of this technology.  the way the designer described it is that it is two different ultrasonic frequencies that have to both be beamed onto a person for the interference frequency to create a "difference wave" in the audible spectrum that then eminates from the recipient's body itself.  

the beauty of it is that it can be triangulated on the target from two distinct sources, so no one else getting just one freq. would hear anything.

it is a novel concept and was not even the same as the link which someone has generously taken the time to give.  the link is informative but I don't think it is the same concept either.

anyway, hope to hear from others that may have info to track this.

[rankus]

Yes.  I saw something about this on the tube about six months ago.   They were touting it as a great tool in crowd control during riots etc.  They could talk directly to people from some distance.  Another application they were planning was military communications under battle field conditions.....


I like the suggested home uses better ;-0

[zmix]

The police had these in New York during the RNC. These were to be used as a weapon against the millions who marched in protest against the rethuglicans.


http://www.sfgate.com/cgi-bin/article.cgi?f=/news/archive/20 04/08/19/politics1557EDT0636.DTL

[arconaut]

I saw this at the last NY AES show two years ago, they were off in a back corner, but there they were with a funny looking speaker which had a paper arrow on it and the words "birds inside".

Sure enough, just when you walked past you could hear birds chirping. If you stepped a half-foot to either side, you heard nothing.

Pretty freaky.