Quiet-List 1997

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Re: Measuring noise



David Staudacher wrote:

>    It would be convenient to have a unit of measure in which distance 
> was already factored in, like the "foot-candle" (or lumen) unit for 
> measuring light intensity.  I think there may already be such a unit. 
> I came across something called "Sound Power Level" (SPL) which I think 
> attempts to do this, but I don't know much about it.  

Hi,

Sound is a variation of pressure. Thus it is defined (amplitude) as a force
on a surface like the velocity is defined in terms of distance and time. So
the distance you may have encountered (SPL) is a surface (normal to the
direction of propagation). The distance between a source and a receiver has
nothing to do with the definition of the sound itself.

About having a unit of measure in which distance is already factored in, I
don't see what you mean, is it that the reading is made each time to the
same distance of the source? Well this is not a bad idea for some cases, as
for printers for example, but it yields to problems (surrounding objets,
location of the printer, the printer itself) of interpretation for
measurements. However this method does not work for outdoor noise (aircraft
and traffic in particular where people ask for ordinances that would limit
the noise levels at their ears and not at a standard distance of the
source).

Regards

			Loc
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