UBC Theses and Dissertations
Acoustical modeling of rooms with extended-reaction surfaces Wareing, Andrew
The acoustical modeling of rooms has always been a great challenge, especially when efforts are made to incorporate acoustical phenomena that are complicated to model. Knowledge of the acoustical behaviour of room surfaces is fundamental to predicting the sound field in a room. Surfaces are classified, acoustically, as of either extended or local reaction. All known room-prediction models assume, whether implicitly or explicitly, that surfaces are of local reaction. How can extended-reaction surfaces be incorporated into room-prediction models? What is the significance to predicted steady-state sound pressures in rooms of surfaces modeled as of extended vs. local reaction? This thesis is a detailed account of research dedicated to answering these questions. The main research goal was to develop a computationally efficient room-prediction model that included phase, and was applicable to rooms with extended- and local-reaction surfaces. A literature review concluded that a combined beam-tracing model with phase, and a transfer-matrix approach to model the surfaces, was the best choice. The transfermatrix model is applicable to extended- or local-reaction surfaces. These surfaces are modeled as multi-layers of fluid, solid or porous materials. Biot theory was used in the transfer-matrix formulation of the porous layer. The new model consisted of the transfer-matrix model integrated into the beam-tracing algorithm. The model is valid for specular reflection only, and calculations were performed in the frequency domain. Both models were validated, and applied to three different room configurations: a 3m x 3m x 3m small office; a 10m x 3m x 3m corridor; and a 10m x 10m x 3m small industrial workroom. The test surfaces consisted of a glass plate, double drywall panels, double steel panels, a carpeted floor and a suspended-acoustical ceiling. Two predictions were made for each test surface in each room configuration - one for extended and one for local reaction. Results showed significantly higher predicted sound-pressure levels in rooms with a suspended-acoustical ceiling modeled as extended reaction, at low frequency. Rooms with walls of double drywall panels modeled as an extended-reaction surface showed significantly higher predicted sound-pressure levels. Sound-pressure levels were shown to be nearly equal in rooms with a single glass panel, carpet, and fibre-glass modeled as an extendedor local-reaction surface. An analysis of the reflection coefficients of these surfaces was performed to explain the results. The results confirm that it can be important to model the extended-reaction nature of room surfaces in some cases.
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