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Low-frequency absorption of sound in airThirty sets of sound absorption measurements in air at a pressure of 1 atmosphere are presented at temperatures from 10 C to 50 C, relative humidities from 0 to 100 percent, and frequencies from 10 to 2500 Hz. The measurements were conducted by the method of free decay in a resonant tube having a length of 18.261 m and bore diameter of 0.152 m. Background measurements in a gas consisting of 89.5 percent N2 and 10.5 percent Ar, a mixture which has the same sound velocity as air, permitted the wall and structural losses of the tube to be separated from the constituent absorption, consisting of classical rotational and vibrational absorption, in the air samples. The data were used to evaluate the vibrational relaxation frequencies of N2 and/or O2 for each of the 30 sets of meteorological parameters. Over the full range of humidity, the measured relaxation frequencies of N2 in air lie between those specified by ANSI Standard S1.26-1978 and those measured earlier in binary N2H2O mixtures. The measured relaxation frequencies could be determined only at very low values of humidity, reveal a significant trend away from the ANSI standard, in agreement with a prior investigation.
Document ID
19850065472
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Zuckerwar, A. J.
(NASA Langley Research Center Hampton, VA, United States)
Meredith, R. W.
(U.S. Navy, Naval Oceanographic Research and Development Activity, Bay St. Louis MS, United States)
Date Acquired
August 12, 2013
Publication Date
September 1, 1985
Publication Information
Publication: Acoustical Society of America, Journal
Volume: 78
ISSN: 0001-4966
Subject Category
Acoustics
Accession Number
85A47623
Funding Number(s)
CONTRACT_GRANT: NAG1-234
Distribution Limits
Public
Copyright
Other

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