Systematic errors in the high frequency predictions of geometrical acoustics software can result from the use of seat absorption coefficients derived by traditional measurement methods based on diffuse-field assumptions. This analysis treats in-situ measurement methods in which seat absorption coefficients are calculated by a diffuse-field model from reverberation time measurements made in auditoria. Computer models illustrate that the nonuniform distributions of absorption in auditoria result in significant differences between the absorption coefficients derived by an in-situ measurement method and the true random-incidence absorption coefficients. Proposals are made for methods to be used when measuring seat absorption coefficients for use in geometrical acoustics software.

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