Quiet-List 1997

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Re: Measuring noise



Message text written by INTERNET:quiet-list@igc.org
>When a whisper is rated at 30 dB, what is left to rate at 20 dB and 10
dB??  If doubling this level to 60 dB brings us to the level of normal
conversation, it just doesn't seem reasonable that another 30 dB increase
should bring us to the level of a power mower.  <


It's my understanding that an increase of 30 decibels would not double the
sound level as one might expect.    Again, the American Academy of
Otolaryngology states:  "as decibel intensity increases by 10 units, each
increase is 10 times the lower figure. Thus, 20 decibels is 10 TIMES  the
intensity of 10 decibels and 30 decibels is 100 TIMES as intense as 10
decibels."  It may not seem reasonable but that's the way the experts say
it works. This is the system we currently have to work with so we should
try to make it work for us.

The distance between a noise source and the point at which it is being
measured may at times be valid information in fully understanding a noise
problem but it is basically the decibel level where the noise is being
perceived that is important.  How or why does it matter how loud the noise
is at its source (or how far that source is from me) unless at that source
it is louder than an applicable regulation allows.  It's the noise level
when it reaches me that is the problem.  Using the figures attributed to
Jeremy Tatum, if a noise originating 3 feet away from me is 58dB and it
interfers with my speaking and understanding, it's a problem.  If, at its
point of origin 500 feet away, it measures 58 dB, I probably don't hear it
and it's not a problem. 

If a person is making a noise on adjoining property and it exceeds 50 dB at
my property line, he is violating the local noise code and he can legally
be told to stop.  That 50 dB measurement, taken at the property line, would
appear to be the critical factor here just as the 58 dB reading is when it
reaches my ear, not what it would register at its source.  It doesn't
matter how far away from that line the noise originates, or how loud it is
at it's source, but how loud it is where it is being heard or measured.  It
is the loudness at its point of perception that most noise laws address and
it's laws to control noise that are at least part of our concern.

To me, that 50 dB(A) measurement of sound at my property line is not
"rather meaningless" at all, just as the 59 dB(A) to 69 dB(A) readings for
the music in the local mall are not meaningless.  They mean the music is
too loud for me to carry on a conversation and they should be forced to
keep their music at or below 55 dB (A). It doesn't matter that the music 
comes from speakers 100 feet above me and might measure 80 dB(A) a foot
from the speaker.  What matters is what it measures at my ear and distance
be damned.

 >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).<

I feel that Loic is correct here and that the basic problem has little to
do with distance but rather with readings at certain levels taken either at
a given geographic point (like a property line) or based on the assumption
that the reading instrument is within a meter or so of the offended or
endangered ears.


STEPHEN O. FRAZIER
SFNABQ@compuserve.com
Writing at 11:53:25 AM on 12/15/97



P.S.....I just took a reading of a person talking on the telephone with no
background noise to speak of and within normal conversation distance from
me.  I used a trusty Radio Shack meter on the fast setting and took an (A)
reading.  The  sound levels  bounced between 52 and 64 .   That averages
out to 58 dB - pretty close to the EPA's 60 and it appeared to me to be a
civilized conversation.  Did the same thing at the dinner table and got
comparable results (until the food fight started).
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