Acoustical Properties of Air versus Temperature and Pressure
Simple algebraic formulas are presented for calculating all the linear acoustical properties of air, except the absorption coefficient, in terms of ambient temperature and pressure. Numerical results are given and compared with published data. Use of the formulas avoids searching for data, ensures that the data are consistent, and facilitates investigation of the effects of ambient conditions on the performance of acoustic devices. The formulas assume dry air; a brief sensitivity analysis suggests that the effects of humidity are of a lesser order of magnitude than those of temperature and pressure. The absorption coefficient, which differs from the other properties in that it is strongly influenced by humidity, can be calculated from the temperature, pressure, and humidity using equations given in ANSI S1.26-1978. But the formulas presented may be regarded as adequate for the modeling of small acoustic devices in which atmospheric absorption of sound waves is not significant.
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