| Summary: | 博士 === 淡江大學 === 水資源及環境工程學系博士班 === 98 === The propagation of sound in long enclosures with branches has been studied theoretically and experimentally, and an efficient combined method is proposed to predict the sound field in long enclosures with branches. Based on the wave-acoustics theory, the theoretical analysis of the sound field of the long enclosures with branches is performed. This paper also investigated the sound field prediction of long enclosures with branches, by using the acoustic modeling program, ODEON. The results obtained by the theoretical analysis and the numerical simulation ODEON are compared with the experimental measurements, and the characteristics of the two methods for predicting the sound field of long enclosures with branches are analyzed. Compared with the experimental results, it is found that: 1) the results predicted by the theoretical analysis fluctuate relatively large with respect to the source-receiver distance, and the sound pressure level (SPL) attenuation obtained is smaller than that measured; and 2) the results predicted by the numerical simulation is smoother, and the calculated SPL attenuation is larger than that measured. To effectively predict the sound field of long enclosures with branches, a combined numerical method is thus proposed. The effectiveness of the proposed combined method is demonstrated by the scale-model experiments. A theoretical model has been developed for the prediction of sound propagation in a rectangular long enclosure. The model is based on the image-source method, and the effect of interference among the infinite number of image sources generated by multiple reflections is incorporated by coherently summing the contributions from the image sources. The various impedances of the boundaries are added in the model. Experiments are carried out to validate the proposed theoretical model, where the enclosure walls are lined with different kinds of sound absorption material to simulate different impedance boundaries. It is shown in the paper that the developed model agrees reasonably better with the experimental data than that of the ODEON software.
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