References: <0b7oAdAR1Zq9Ewqf@jmwa.demon.co.uk> <email@example.com>
Subject: Re: Coming soon to a theatre near you - endless mischief potential
X-Newsreader: Microsoft Outlook Express 5.00.2919.6700
Date: Mon, 14 Oct 2002 03:15:08 GMT
NNTP-Posting-Date: Mon, 14 Oct 2002 03:15:08 GMT
Organization: AT&T Worldnet
I have heard someone on a skate-board come near a house on the opposite side
of my window at 4 am and project a sound that was straight out of a sci-fi
movie ( a pre-historic bird call type - kriek-kriek-kriek... ) up to the
window of that house. < This was a few months ago >
Before I could turn around, the person was gone (rolling on the
This could not happen unless the unit was compact and hand-held etc.
"milne_v" wrote in message
> John Larkin wrote in
> > On Sun, 13 Oct 2002 18:25:26 GMT, James Meyer
> > wrote:
> > >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
> > >and that creates an area where the interference occurs and the audible
> > >produced. Sound isn't produced or directed along either beam, but only
> > >the beams come together. That is what allows the production of sound
> > >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.
> > >
> > >Jim
> > Jim,
> > 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.
> > John
> 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.