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Re: Regulation & Road Noise (fwd)
Sorry if this message is redundant. I didn't see it on the list. Also,
note I've corrected an error here.
> The criterion "beyond 30 ft the sound should disappear" has little
> meaning without a number behind it. Should it be less than 10% of the
> ambient? in sound pressure? in energy? Numbers are needed to give flesh
> to criteria for a quieter and more pleasant environment.
Depending on frequency and sound pressure level, psychoacoustic masking
effects begin to be noticeable (that is, a sound becomes inaudible in
the presence of another one) when the sound presure level goes some
20 dB below the masking sound. Of course this is a rough criterion,
because a high-pitched tone won't mask a low-pitched one at all, almost
regardless of its sound pressure level.
So, if numbers are to be included, one should say that, roughly, in order
to be inaudible sound or noise should be at least 20 dB below the ambient
noise level. This means that the presence of the unwanted sound should
increase sound level in not more than 0.043 dB [there was a mistake here
the first time I posted this message].
Anyway, may I insist on this being a rough, just-to-begin-with hypothesis.
Taking into account that music is a discrete-spectrum kind of sound,
whereas ambient noise is a continuous-spectrum one, this is likely to be a
rather permissive criterion yet.
I'll try to think a bit more about this, and if I reach any interesting
result I'll post it to the list.
Incidentally, 20 dB below means 10 % in sound pressure and 1 % in
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