Re: Clarke - two questions

Richard Todd <rmtodd@[EMAIL PROTECTED]
> writes:

>Did the noise canceler in the story cancel just noise in a region next to

>your ears, as the current noise-cancelling headphones do, or did it
cancel
>noise in a much wider area?  

>I remember thinking about this while reading Flint and Weber's _Crown of 
>Slaves_, where a noise-cancelling device is a (minor) plot point in one
scene.
>I'm not sure I buy the notion that you could make a device that could
listen
>to the ambient sound and accurately produce counter-waves sufficient to 
>almost perfectly cancel all sound through, say, an entire room.  Not even

>given that Solarian or Manty mollycirc hardware is probably as much
faster than
>current DSP hardware than that hardware is compared to the first Intel
4004
>microprocessor.   I don't buy that good-enough cancellation over a wide
>area would be possible, given the finite propagation time of sound waves.


	As it happens sometime last year I ran across a news report 
of an experimental device to significantly reduce crowd noises.  The 
intended application was that noise cancellation should be able to keep 
football/soccer chants from spilling out into open rebellion and the 
occasional invasion of a neighboring nation, although I recall one of 
the quoted figures wondering whether a crowd trying to get a chant going 
and finding just no success would find itself more agitated. 

	A quick search of the BBC News web site shows I can't pull up 
the proper keywords for it.  I *think* the gadget was supposed to work 
by a pretty basic slight delay and clever bit of amplification.  I may 
have read it on Reuters instead, but their archives are more difficult 
for me.  

	I apologize for having such an inadequate citation, and I hope 
it wasn't some silly thing I ran across in New Scientist.  

-- 
								Joseph Nebus
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