Atmospheric Absorption of Sound: Theoretical Predictions

TLDR

The study predicts atmospheric sound absorption by modeling air as a mixture of nitrogen, oxygen, water vapor, and carbon dioxide and applying energy transfer rates for binary collisions. The authors model atmospheric sound absorption using 24 energy transfer mechanisms, compare calculated curves with experimental data across 0–100 % humidity, and include classical absorption and rotational relaxation effects to predict total absorption at 20 °C. Theory agrees well with experiment; CO₂ below 0.1 % has negligible effect on audible sound absorption at high humidity, but becomes significant at very low humidity.

Abstract

By assuming that air is composed of four gases (i.e., nitrogen, oxygen, water vapor, and carbon dioxide) and applying energy transfer rates for the binary collisions inherent in such a system, absorption of sound in the atmosphere has been predicted. The calculated curves based upon 24 energy transfer mechanisms are compared with experimental data over the humidity range of 0–100% relative humidity. Agreement between theory and experiment is very good. By including classical absorption and rotational relaxation effects, the total atmospheric absorption is also predicted at 20°C. Calculations made for various concentrations of CO2 indicate that low CO2 levels (less than 0.1%) do not significantly affect absorption of audible sound at high humidities. At very low humidities, however, CO2 is an important factor.