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Re: Measuring noise
On Sun, 14 Dec 1997, David Staudacher wrote:
> Britannica article and Stephen's AAO pamphlet. I think we should
> strive to make distance a routinely expected part of any decibel-based
> statement, just as we routinely expect velocity to be stated in terms
> of time and distance. No one should accept one without the other.
> from 1 thru 10, I would propose something like the "foot-bel" as a
> standard unit. On such a scale, everything would be stated in terms
> of a standard distance.
I agree that a standard should be used when quoting dBs. When I see dBs
quoted in papers/articles I automatically assume that they are dB(A). I
then "assume" that they were measured a few feet from the noise source.
This assumption isn't good enough of course.
Our organizations should be pushing manufacturers to label their
sound-emitting equipment with a standard dB system that incorporates
distance into the figures. Right now the manufacturers are
all over the map. Most do not label their equipment. Those that do use
varying "standards". For example Canon labels their bubble jet printers
for noise levels. Their BJC-240, BJC-4200, and BJC-4300 are all rated at
45 dB(A). No distance is mentioned.
We should be encouraging manufacturers to label their products for noise
levels, but using a standardized method. If two manufacturers measure
their products to have a sound level of 45 dB(A), it's still possible for
one of them to be twice as loud as the other!
> the low end of any noise scale. When a whisper is rated at 30 dB,
> what is left to rate at 20 dB and 10 dB??
I'm not sure whether you are taking into account the nature of the
dB logarithmic scale. A 20 dB sound would sound half as loud to our ears
as a 30 dB whisper (it would in fact have 10 times less sound energy).
There are many sounds that could be produced in this 20 dB range that we
could still hear.
> 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. I know that logarithmic scales can be
Going from 30 dB to 60 dB should _never be viewed as doubling. It is
1000 times the sound energy level and sounds 8 times as loud to our ears.
So going from 60 dB to 90 dB (a power mower) is adding 1000 times the
sound energy level and sounds 8 times as loud as the 60 dB sound.
I hope that shortly an international standard is set up to measure
sound levels which incorporates distance in the measurement _and uses the
(C) scale or a scale which weights the lower sound frequencies to be as
important if not more important than the mid and higher frequencies.
After all it is the low frequencies which disturb people when they hear
car stereos, home stereos, airplanes, automobile traffic etc.
I was in an electronic store several months ago and took two sound level
measurements. One using the (A) scale and one using the (C) scale. The
sound registered approximately 60 dB(A) and more than 80 dB(C). I became
a (C) scale convert immediately. The noise was very annoying.
President - NoiseWatch
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