Simplified procedure for computing the absorption of sound by the atmosphere

This paper describes a study that resulted in the development of a simplified method for calculating attenuation by atmospheric-absorption for wide-band sounds analyzed by one-third octave-band filters. The new method [referred to herein as the Volpe Method] utilizes the accurate pure-tone sound absorption algorithms of two published standards, the International Standard, “Acoustics-Attenuation of Sound During Propagation Outdoors-Part 1: Calculation of the Absorption of Sound by the Atmosphere,” ISO 9613-1 and, the American National Standard, “Method for Calculation of the Absorption of Sound by the Atmosphere,” ANSI S1.26-1995. The purpose of the study was to extend the useful attenuation range of the Approximate Method outlined in the ANSI document, and provide a basis for replacing the current Society of Automotive Engineers Aerospace Recommended Practice 866A, “Standard Values of Atmospheric Absorption as a Function of Temperature and Humidity” (SAE ARP 866A). The Volpe Method was found to be useable to mid-band absorption levels up to 500 dB with errors of less than ±0.5 dB or ±5% (of mid-band attenuation levels) to 100 dB, and ±7% to 500 dB.