In a message dated 10/26/02 6:08:22 PM Central Daylight Time,
owner-ax-digest@autox.team.net writes:
<< If a sound is 7db over "stock" is that a significant increase? This
relates to
interior muffler noise or resonance. >>
The other responses were technically correct, but there is one big thing that
meters can't really show. That is the frequency spectrum of the sound. If it
was a nice melow sounding 87 db before, and now it is a raspy 94 db, it could
sound much much louder, but if it was a raspy mettalic 87 db, and it is now a
mellow 94 db, it might actually be more pleasent. Noise measuremtns for
hearing sfet (OSHA) and for most noise complain tests are done using the "A"
weighting scale. This measures the sound pressure through a filter which is
close to the spectrum of the human ears most sensitive region, upper
midrange. When I set theatre sound levels, we set them to 85 db using "C"
weighting. Switching the meter to "A" weighting usually shows about a 5 db
drop since it is filtering out much of the low frequency energy. We set the
sub woofers at 95 db, but just in the active region up to 200 hz. Even the C
weighting shows this as less than 85 db, and A weighting is almost nil.
A very loud rumbling car could show very low A weighted sound levels. But
squealing tires could be over 100 db A.
Gary M.
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