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From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: Coming soon to a theatre near you - endless mischief potential
Date: Sat, 12 Oct 2002 19:35:12 GMT
NNTP-Posting-Date: Sat, 12 Oct 2002 12:35:12 PDT
Winfield Hill wrote:
> A tightly-focused beam could be aimed directly at a person from a
> long distance away; most of the low-frequency sound is generated
> along the pathway, with very little of the original high-frequency
> arriving because of very high HF ultrasonic attenuation in air (I've
> posted that data here several times). Thus announcements could
> be conveniently aimed just at a person or a small group of people.
> This technology has been explored for 10 years by Pompeii at MIT.
It can't be quite that simple. If mixing occurs along the path the low
frequency is generated with small aperture at a distance and diffraction
will cause enormous beam spreads. The mixing really needs to be near the
target to avoid this problem.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons firstname.lastname@example.org
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