From: email@example.com (milne_v)
Subject: Re: Coming soon to a theatre near you - endless mischief potential
Date: 13 Oct 2002 20:07:51 -0700
References: <0b7oAdAR1Zq9Ewqf@jmwa.demon.co.uk> <firstname.lastname@example.org>
NNTP-Posting-Date: 14 Oct 2002 03:07:51 GMT
John Larkin wrote in message news:...
> On Sun, 13 Oct 2002 18:25:26 GMT, James Meyer
> >On Sun, 13 Oct 2002 11:05:09 -0700, John Larkin
> > wroth:
> >>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.
It's single beam, dual beam used to be used. The process is explained
for single beam. We'll just have to wait and see what the products do.
Holosonics originally from MIT Medialab has units operating in museums
etc. I don't have any problem with the single beam dynamics, I have
problems with the transducer coupling being able to move enough air
to achieve the power levels at the distances mentioned. If the
products hit the market then I'm sure they'll get a good technical
working over. One problewm I did hear about was that the product could
cause some inner ear irritation to the listener if the beam struck the
eardrum straight on.