Quiet-List 1997

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Re: Technology and Coping

>     Will someone explain this to me? 
>     How can noise be "cancelled"? 
Michael Wright

  David has done a pretty good job with his explanation. Somewhere on one
of my computers I have a 10 or so page document detailing the technical
side to noise cancellation principles. All that needs to be understood is
that in theory, if a sound wave of amplitude and frequency that is a
mirror image to the original sound wave, is directed at the original wave,
then it should cancel it out, leaving nothing to be heard. 

 In a nutshell, although the priciple of this technology is quite
straightforward, in practice it is extremely difficult to pull off
successfully. There are several companies trying to capitalize on the
virtually unlimited amount of uses that such technology would afford. 
Unfortunately, to date there are few commercial applications that directly
help the public. The most common uses in practice today are in aircraft
cabins, and some European/Japanese subway trains. Aircraft pilots have
been using NC headphones for several years now. Experiments are being
carried out in various automobile vehicles as well. 

 To link this back to our discussion...  NC technology is very limited
today in its applications. For the most part, it is most successful in
countering *specific* predictable noise sources. It also targets sounds
which belong to the low-end of the sound frequency spectrum with more ease
than those of the mid-high range.  

 As quiet-list members, most of us are aware of the three general 
locations to counter noise: at the source, at
the receiver, and somewhere in between. NC works best operating on the
source. For applications such as Peter's heat pump example, this would
work out very nicely if implemented properly. This example is very
achievable with today's NC technology.  

 David was pointing out was that in many circumstances, technology 
is undesirable and unnecessary to
resolve noisy situations. If a person is making unnecessary and
unreasonable noise, then that person should cease that behaviour
immediately, or rather never begin it in the first place.  Bringing in the
latest and greatest technology can help, but shouldn't be relied upon to
conquer many of our noise problems.  

 Wouldn't you know it. She finally makes her first Quiet-list post and is 
pounced upon from all directions <g>. 

 Eric Greenspoon
  Vice President - Citizens' Coalition Against Noise

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