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From: brent@terra.UUCP
Newsgroups: rec.aviation,sci.electronics,rec.audio
Subject: Re: Noise-cancelling microphone
Message-ID: <19549@sun.uucp>
Date: Fri, 22-May-87 13:02:40 EDT
Article-I.D.: sun.19549
Posted: Fri May 22 13:02:40 1987
Date-Received: Sat, 23-May-87 10:49:33 EDT
References: <1027@mips.UUCP> <689@cod.UUCP> <867@lll-lcc.aRpA> <2849@mit-hermes.AI.MIT.EDU>
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Summary: leg pull ?

In article <2849@mit-hermes.AI.MIT.EDU>, jpexg@mit-hermes.AI.MIT.EDU (John Purbrick) writes:
> 
> Regarding noise-cancelling speakers and mikes, there was an article in the
> British magazine "New Scientist" a while back about the use of "anti-noise"
> near large sources of acoustic noise like stationary gas turbine installations.
> The idea was to put a microphone some way from the device and drive a speaker
> adjacent to the device; an electronic system would try to null out the
> resultant signal as measured at the mike. As I recall the system was claimed
> to work fairly well, but I don't recall the db figures or how they solved
> the obvious problem of delay from the noise sources to the mike.


Sounds like New Scientist is putting one over you.  It's
certainly not this easy (possible ?) to do this in an
open acoustic field.  It reminds me of an Aurthur C. Clarke
story in "Tales of the White Hart" where someone invented one
of these sound-nulling gadgets and had fun with it.

I remember some years ago reading a similar article in
New Scientist about an optical element that had just been
invented for large telescopes that corrected images that
lay at the extremes of the telecopes' field.

The developers of this element were reported to be very
excited at the commercial possibilities of the element
when applied to corrective lenses for people.  The human
eye can resolve detail sharply over a small area at the
center of the visual field.  The new element would correct
off-axis images so that the high visual acuity would extend
over the whole visual field.  The amount of eye movement
in scanning an extended image would be greatly reduced.
As an example they suggested that inspection of posted train
timetables would be greatly facilitated.

I've seen articles in similar vein in Scientific American.
Was it the April 1st issue ?

Made in New Zealand -->  Brent Callaghan  @ Sun Microsystems
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