Quiet-List 1997

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Inadequacies of the A-Scale



In a message dated 97-11-30 00:38:14 EST, you write:

<< Believe it or not, but the A-weighted scale was intended as a
 temporary measure - but after everyone started using it iot has sort
 of stuck...
 
 There is a better parameter available - known as "Loudness" - this is
 more complex as it takes better note of the frequency distribution of
 the noise. Unfortunately, there aren't many cheap loudness meters
 around yet (actually, come to think of it, I can't think of any...). >>


The A-scale is useful when the sound falls between, say, 750-4000 Hz. It is
completely inadequate when the sound is below 750 Hz, such as the bass
component in music. Octave band analysis is useful here, and is well
established with plenty of legal precedent. Octave band analysis can be time
consuming (if the technician does not have a lot of practice) and the meter
is relatively expensive. 

I think that the C-scale may be useful, as it does not eliminate as much of
the low frequencies as does the A-scale. It is on practically every meter
sold, and you would not have to turn around a whole industry (sound level
meter manufacturers.) Setting permissible C-scale levels could not be
arbitrary. This could bear some investigation, with studies determining the
C-weighted levels at which speech and sleep interference occurred, as was
done for the A-scale in EPA's Levels Document. This would be a useful
endeavor, and I have discussed it with several jurisdictions. However, none
wants to be the ground breaker. Also, human subject studies are unspeakably
complex, expensive and time consuming. If EPA's ONAC is reopened, this might
be a useful thing for them to get into.

Eric Zwerling
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