A new approach to the effect of bandpass filters on sound absorption calculations

Abstract

Atmospheric absorption losses are usually calculated for single frequencies, but must often be applied to bandpass-filtered data, usually in octave bands or one-third octave bands. The simplest approach, using the absorption value at the bandpass filter center frequency, is inaccurate for broadband sources when the losses are large because the resulting spectrum has a large negative slope with frequency, and thus the band level is dominated by power near the lower band edge. The proposed new approach uses a representative frequency at which absorption is calculated and which depends on the total absorption along the path. An expression for the representative frequency is derived and errors are evaluated for several cases. A practical method, suitable for hand or computer implementation, is proposed.s