REPRESENTATIVE FREQUENCY APPROACH TO THE EFFECT OF BANDPASS-FILTERS ON EVALUATION OF SOUND-ATTENUATION BY THE ATMOSPHERE

Pure tone attenuation coefficients for computing attenuation from atmo spheric absorption cannot always be applied accurately to determine th e corresponding total attenuation of a broadband sound analyzed by fra ctional-octave-band filters. This total band attenuation depends on th e finite width and shape of the bandpass filters and the strong freque ncy-dependent characteristics of atmospheric attenuation, A new theore tically founded and empirically refined method is outlined that makes it possible to determine the band-level attenuation of a broadband sou nd analyzed by fractional-octave-band filters for given meteorological conditions along a sound-propagation path, The method is based on rep resenting the one-third-octave-band attenuation by the pure-tone atten uation at a single representative frequency. However, unlike other suc h methods, the representative frequency is a function of the total pur e-tone attenuation over the propagation path at the exact midband freq uency, The new method provides results that are much more accurate tha n, and comparably as easy to apply as, the method contained in the Soc iety of Automotive Engineers Aerospace Recommended Practice ARP 866A:1 975. Application of the method is illustrated for (a) evaluation of at mospheric propagation loss of broadband souud through a homogeneous at mosphere and a nonuniform layered atmosphere and (b) volume absorption for broadband sound in room acoustics. (C) 1996 Institute of Noise Co ntrol Engineering.