Quiet-List 1997

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Re: Measurement/Question/Sensitivity



John Darcy Evans wrote:
> 
> Dear List:
> Measurement:
> I believe we are re-inventing a lot of wheels!  The physics of sound
> propagation is well understood and good libraries will have copious
> material!
> European countries have standards and codes of practice for the
> prediction of road traffic and airport noise as well as recommendations
> for maximum ambient levels in internal environments and for speech
> intelligibility.  I would be surprised if the USA and Canada don't have
> equivalent codes [even South Africa is well armed with these].
> Ideally, noisy equipment should be specified by maximum permissible
> sound power level. As this is extremely difficult to measure in the field,
> an in-situ maximum permissible sound pressure level has to be specified;
> alternatively, a maximum free field sound pressure level at a defined
> distance.  For free field hemispherical sound propagation [ie usual short
> range circumstances], the sound pressure level derived from a given
> source drops by roughly 6dB for every doubling of distance from the
> source. [BUT dB's are not a measure of annoyance!]
> Question/Sensitivity, etc.:
> In terms of sheer weight of damage to human civilisation, I am sure that
> noise is among the top 10.  However, I remain convinced that the only
> way forward for us anti-noise activists is to quantify noise damage in
> terms of hard cash and that means research.  It means hard cash to
> move an airport or road and it costs hard facts for the legislators and
> courts to take noise seriously, even if part of those hard facts have to be
> the realities of aggresive political agitation and lobbying.  Cigarette smoke
> is easier to get a grip on than noise and therefore noise will be
> correspondingly more difficuflt to overcome.  I expect the processes will
> have to be much the same - ie established, repeatable Health/Noise
> correlation and un-questionable cost apportionment followed by long and
> focused lobbying.
> A ray of light at the end of the tunnel seems to be the intention of the
> British Government to research the social cost of noise during 1998.
> Hopefully, the end of 1998 will therefore present us with something
> meaningful to build on, even if it has emerged from a European context.
> Regards ...
> 
> John D'Arcy-Evans
> tel.:     (021) 400 3860
> fax:     (021) 419 7096
> E-mail: jdevans@ctcc.gov.za
> 
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Measurement and sensitivity to noise can be more closely related than is
commonly practiced.  But it gets technical and is best discussed
graphically.  But the basic concept is this:

People are less sensitive to a sound environment that is considered
"white noise".  Among the characteristics of white noise are (1) it is
constant in sound level, and (2) the frequencies are distributed over a
wide range.  A large waterfall is an example of white noise. 
Sensitivity to sound levels can be estimated by using factors that
include both the sound level and the "white noise" character.  Both can
be determined from measurements, provided that the measurements are
sufficiently frequent.  I have developed a rating method for noise based
on this approach.
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