The discovery in the 1960s that sound was seriously attenuated at bass frequencies when it passed over audience seating presented a puzzle: Why had this behavior not been detected subjectively? The results of a measurement program in 17 British concert halls are used to establish the magnitude of effects on sound spectra caused by reverberation time frequency characteristics, grazing incidence, and other effects. Two design features were found to produce excessive bass sound attenuation: ceiling designs which obscure reflections from above and hall shapes responsible for poor diffusion for later sound. It is concluded that average effects due to grazing incidence can be compensated by a rise in bass frequency reverberation time.
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