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Klarinet Archive - Posting 000889.txt from 2001/02

From: Oliver Seely <oliver-seely@-----.net>
Subj: Re: [kl] You never know who'll you meet ...
Date: Fri, 23 Feb 2001 11:28:13 -0500

Well, O.K., but the rhetoric seems to be that of the inventor, Pompei, not
an independent observer. Moreover, it isn't clear if the "ultrasound" near
the emitter array (the "Audio Spotlight") is an amplitude modulated
millimeter wavelength emission described later or something else. The
conversion from inaudible "ultrasound" to something that can be heard seems
to be constructive interference at some known distance from the emitter,
though the principle is never described.

There's a lot of hype mixed in with the interesting stuff, in my opinion.
For example, the paragraph

"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."

makes me think that Pompei would be good at marketing herbal remedies. He
reminds me a little of some of our electronic music majors who haven't yet
taken enough physics to know what they're talking about.

Oliver

At 10:58 PM 2/22/01 -0600, you wrote:
>Sitting next to me at a chamber music concert a few days ago was Mary Beth
>Bennet, a professor at UT who does acoustics work. We got to talking about
>non-linear sound perception. She turned me on to non-linear sound
>propagation! Here's a little fun page about non-linearities in sound
>propagation:
>
>http://sound.media.mit.edu/~pompei/nonlin/nonlin.html/
>
>In 1975, Mary Beth Bennett and David T. Blackstock, both at the University
>of Texas at Austin, were the first to demonstrate the effect, and this page
>discusses one of the more interesting aspects.
>
>Mark C.

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