From: John Larkin
Subject: Re: Coming soon to a theatre near you - endless mischief potential
Date: Sun, 13 Oct 2002 11:54:19 -0700
Organization: Posted via Supernews, http://www.supernews.com
References: <0b7oAdAR1Zq9Ewqf@jmwa.demon.co.uk> <firstname.lastname@example.org>
X-Newsreader: Forte Agent 1.91/32.564
On Sun, 13 Oct 2002 18:25:26 GMT, James Meyer
>On Sun, 13 Oct 2002 11:05:09 -0700, John Larkin
>>So, after the ultrasonics haved faded away, the low-frequency audio
>>obligingly remains in the same tight beam, traveling in the original
>>single direction, even for wavelengths that exceed the beam diameter,
>>and are audible only within the narrow cone of the beam.
> It's my understanding from a quick look at the technique some time ago
>that TWO beams are used. The axis of the beams intersect at a point somewhere
>and that creates an area where the interference occurs and the audible sound is
>produced. Sound isn't produced or directed along either beam, but only where
>the beams come together. That is what allows the production of sound at
>particular spots remote from the ultrasonic sources and not at others.
> A single ultrasonic lifeguard megaphone seems to be an unwarranted and
>bogus extrapolation of the existing techniques.
right, the two-beam thing, at least qualitatively, has a chance of
working. The sources will of course have to be far apart to get the
angles wide enough to target a reasonably small spot. But both
American Technology and Holosonics (not to mention the august Popular
Science) show a single, roughly 1-square-foot, source, and claim all
the bizarre features I have questioned.
The concept of a single ultrasonic 'tube' confining the generated
sonics is, as you point out, bogus.