Effects of aperture diffraction on reverberant energy decay in coupled-room auditoria are estimated at mid frequencies, defined as frequencies above the Schroeder frequencies of subrooms, but having wavelengths of the order of the characteristic dimensions of apertures. Hybrid models are developed that account for wave effects at apertures but treat sound fields in subrooms using high-frequency models. The models give more accurate estimates of the random-incidence power transmission coefficient. These estimates agree well with independent measurements of circular apertures in thin, hard screens. When used to predict the effects of diffraction in a schematic representation of typical coupled-room auditoria, new mid-frequency models suggest that effects of diffraction on decay curves, while smaller than variations due to input-parameter uncertainty, are large enough to be audible.
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