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Targeted Sound Beams
Mr_Kcleen writes: "Wired has a story on using sound beams targeted to only one person. They discuss various uses, from musical performances to possible weaponization." This is another one of those ideas that are right around the corner, really, honest.
The New York Times is also covering the article (free reg) or you could just go to The Audio Spotlight's home page for a more detailed account of their technology.
Pompei's website hase more detailed information of this here: http://web.media.mit.edu/~pompei/spotlight/ here is a brief description from the site. Technology: Because it is impossible to generate extremely narrow beams of audible sound without extremely large loudspeaker arrays, we instead generate the sound indirectly, using the nonlinearity of the air to convert a narrow beam of ultrasound into a highly directive, audible beam of sound. The device transmits a narrow beam of ultrasound (blue), which, due to the inherent nonlinearity of the air itself, distorts (changes shape) very slightly as it travels. This distortion creates, along with new ultrasonic frequencies, audible artifacts (green) which can be mathematically predicted, and therefore controlled. By constructing the proper ultrasonic beam, this nonlinearity can be used to create, within the beam itself, an audible sound beam containing any sound desired. This is presently done in real-time using low cost circuitry, a specially designed amplifier, and transducers developed at MIT specifically for this project.
Saying Java is nice because it works on all OS's is like saying that anal sex is nice because it works on all genders.
This was reported in Scientific American in 1998. I also recall seeing it in New Scientist, and on the BBC television programme, "Tomorrow's World" at about the same time.
"E pur si muove!" - attributed to Galileo Galilei, 1564-1642
to directing sound with a parabolic lens.
In its broadest sense the problem with any transmitting antenna, be it sound, light or radio frequencies, is diffraction
For a given wavelength the smaller the space you emit the waves from the wider the angle they spread over.
What these people have done is to use the improved diffraction characteristics of high frequency ultrasound, which diffracts far less than ordinary audio frequencies to generate audio sound literally "out of thin air" due to a nonlinear interaction within the air.
Hats off to Mr Pompei, it sounds like a very neat system. (I couln't help the pun, sorry)
Be nice to people on the way up. You will meet them again on your way down!