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UBC Theses and Dissertations

Acoustical modeling of the transient response of rooms using a beam-tracing model Yousefzadeh, Behrooz


Two room-acoustical prediction models were previously developed in the UBC Acoustics and Noise Research Group and used for studying the steady-state responses of various room configurations. The first is a wave-based beam-tracing model for empty rooms with specularly-reflecting, extended-reaction surfaces. Room surfaces were modeled as multiple layers of elastic solid, fluid and poroelastic materials, and their acoustical properties were calculated using a transfer-matrix approach. The second model, PRAY, is a wave-based ray-tracing model which can account for fittings, diffuse surface reflection and sound diffraction. This thesis presents further development of the existing beam-tracing model, incorporating features from PRAY such as diffuse reflection. The computational efficiency of the existing model has been improved and energy-based prediction has been implemented. Both wave- and energy-based modeling have been validated against theory for the case of sound propagation above a rigid plane. The new model can predict the pressure impulse response between the source and receiver, which is required for obtaining the temporal response of rooms to other sound sources, as well as for deriving room-acoustical parameters that correlate with subjective perception of sound. The new model is used to compare the effects of different surface-reaction models on the transient response and derived room-acoustical parameters. In addition to investigating the significance of modeling room surfaces as of extended or local reaction, effects of phase changes due to surface reflections have been studied by considering real and complex reflection coefficients. Moreover, wave-based energy impulse responses and room-acoustical parameters have been compared with those obtained from energy-based modeling. Modeling of diffuse surface reflections has been implemented in the model and validated against existing experimental results. The model has been further extended to include sound diffraction around wedges based on an exact formulation. This broadens the application of the model to situations with more realistic features, such as sound propagation in fitted rooms or in long enclosures with bends, and evaluation of screen barriers in open-plan offices. The implemented diffraction model has been validated through comparison with existing results in the literature, and by comparing prediction results with experiments on a finite-length barrier over a flat surface.

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