Measurement of the Rate of Decay of Sound in Small Chambers for Frequencies to 11,000 cycles, and a Determination of the Effects of Temperature and Humidity on the Absorption of Sound in Air

A modification of the Norris-Andree method of measuring the rate of decay of sound in small chambers has been developed which operates satisfactorily for frequencies up to 11,000 cycles. The rate of decay, in db per second, in cubical chambers 6 feet and 2 feet on an edge, is accurately linear over a range of at least 60 db. The equipment has been used to determine the effects of temperature and humidity on the absorption of sound in air. The results obtained confirm those obtained by the author two years ago, but the measurements have been extended to higher frequencies, to dryer air, and to temperatures between 0 and 70°C. The results exhibit further evidence of the absorption of sound owing to the transfer of energy by collisions of H2O and O2 molecules (see abstract by H. O. Kneser, Bull. Am. Phys. Soc. for Washington meeting, April, 1933). The apparatus also is convenient for measuring the absorption coefficients of small samples of acoustical materials, especially at high frequencies.