Volume 118, Issue 3, September 2005
Index of content:
- ARCHITECTURAL ACOUSTICS 
The effects of simple coupled volume geometry on the objective and subjective results from nonexponential decay118(2005); http://dx.doi.org/10.1121/1.1984892View Description Hide Description
This project focuses on the individual and interactive acoustic effects of three architectural parameters on the double slope profile from a simple coupled volume system created in the computer modeling program ODEON. The three variables studied are the volume ratio between the main and secondary spaces, the absorption ratio between the two spaces, and aperture size. The resulting energy decay profiles are analyzed using coupling coefficient ratios and Bayesiananalysis. Coupling coefficient results show general trends in the effects of the three architectural parameters that match previous research results and the predominant interactive effect between the three variables involving a large coupled volume. Similar results are suggested by the Bayesiananalysis based on the newly developed quantifiers, decay ratio and , although a more complex relationship among the variables may exist at larger volume ratios. A subset of the simulated sound fields have been auralized and used to conduct psychoacoustictesting. The subjective testing results indicate that perceived reverberation increases with greater coupled volume size and aperture size, correlating well with objective results. The outcomes also suggest that higher perceived reverberation coincides with larger decay ratios and smaller values. Subjective results based on clarity showed no significant effects.
Adapting a randomized beam-axis-tracing algorithm to modeling of coupled rooms via late-part ray tracinga)118(2005); http://dx.doi.org/10.1121/1.2000772View Description Hide Description
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.