Attenuation of Audible Sound in Fog and Smoke
Vern O. Knudsen, John V. Wilson, and Neal S. Anderson
University of California, Los Angeles, California
(Received July 19, 1948)
Measurements of the rate of decay of sound in a reverberation room, first with no fog or smoke in the room and then with fog or smoke of known concentration and particle size added to the room, show that the attenuation of sound in a number of aerosols is in approximate agreement with values predicted by the theories of Sewell, Epstein, and Oswatitsch. In a water fog having a concentration of 2.0×10–6 grams/cm3 and average droplet radius of 6.25×10–4 cm, the attenuation owing to the fog increased from about 5 db/sec. at 500 c.p.s. to 13 db/sec. at 8000 c.p.s. In a quite similar fog of mineral oil, the corresponding attenuation increased from 1.6 db/sec. at 500 c.p.s. to 21 db/sec. at 8000 c.p.s. At very low frequencies, a fog of water is much more absorptive than is a fog of oil; the difference is ascribed to a “relaxation” effect of evaporation from and recondensation the droplets, which is much greater for water than for oil. The attenuation of sound in smoke may become rather high, amounting to 58 db/sec. at a frequency of 6000 c.p.s. for a moderately dense smoke of NH4Cl (180 g in a volume of 6080 cu. ft.). ©1948 Acoustical Society of America
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See Also:
Propagation of Sound Through Atmospheric Fog
Measurements of the Attenuation of Sound by a Warm Air Fog