The ability of computational geometrical acoustics to accurately model energy decay in systems of coupled rooms is investigated both theoretically and experimentally. Unlike single-volume rooms, coupled rooms have reflection density that is not described by a single quadratic function of time. It is shown that tail-correction procedures used by beam-axis-tracing algorithms, which assume quadratic growth of reflection density, can lead to inaccurate predictions in coupled rooms. Further, beam-axis tracing implemented as ray tracing with a growing detection sphere is susceptible to error in coupled rooms when the detection sphere extends into adjacent subrooms. Marked error is anticipated in those cases for which the source and receiver are in the less reverberant of two rooms and is expected to be most severe for (1) small coupling apertures and (2) receiver positions near boundaries between subrooms. Errors are demonstrated by comparison of computational geometrical acoustics predictions with scale-model measurements made in a two-room coupled system. A revised beam-axis∕ray-tracing algorithm is investigated that circumvents possible error mechanisms by switching to ray tracing for the late part of the decay. Comparisons with scale-model measurements indicate that the revised algorithm is able to predict energy decay accurately in coupled rooms.

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