### ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

## 2aNS5. Applications of the proposed new method for computing attenuation
of fractional octave bands of a wideband noise by atmospheric absorption.

**Paul D. Joppa
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*Boeing Commercial Airplane Group, P.O. Box 3707, MS 67-ML, Seattle, WA
98124-2207
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**Louis C. Sutherl
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*Rancho Palos Verdes, CA 90274
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**Allan J. Zuckerwar
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*NASA Langley Res. Ctr., Hampton, VA 23681-0001
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A simple method for computing the attenuation due to atmospheric
absorption for fractional octave bands of noise, outlined in a previous paper
[P. D. Joppa, L. C. Sutherland, and A. J. Zuckerwar, J. Acoust. Soc. Am. Suppl.
1 88, S73 (1990)], is briefly reviewed and example applications to aircraft
noise and room acoustics presented. The method uses an analytical approximation
of a ``representative'' frequency for which the pure-tone attenuation loss due
to atmospheric absorption is equal to the actual loss for the band of noise.
The resulting total band attenuation, (delta)Lb for propagation over a distance
s, for a band with an exact midband frequency f[sub m], is equal to a nonlinear
function of the total pure-tone attenuation a(f[sub m])(centered dot)s over
this path where a(f[sub m]) is the pure-tone attenuation coefficient at the
exact midband frequency f[sub m]. The method provides better estimates than in
SAE ARP 866A for the true band attenuation when the total true band attenuation
is less than about 50 dB. For application to room acoustics, it is shown that
the ``distance'' s involved is simply equal to the reverberation time, T times
the speed of sound in the room.