揚聲器於不同空間聲傳行為之研究

Abstract

本文主要探討管道幾何類型及尺寸與消音量關係，分為管壁吸音係數、外在基礎管路幾何形狀設計及細部管路設計。研究方法主要分為兩部分，第一部分以有限元素軟體ANSYS模擬分析聲音在開放空間及外接管路中輻射情況，驗證揚聲器及空氣元素模型在聲場流固耦合分析之可行性，開放空間中空氣模型聲壓與距離的關係符合點音源衰減公式。在管路分析部分提出簡化的分析模型，能有效降低時間，驗證含空氣有限元素模型之正確性。第二部分改變外接管路幾何形狀及管壁性質，提供具膨脹腔消音管幾何尺寸設計依據。依據以上分析參數結果，歸納出設計參數對消音器之消音性能影響，以設計符合減噪頻率之消音器。

This thesis studies the sound propagation in different hollow bodies and the factors that can reduce the sound pressure level inside or at the exits of the bodies. The contents of the thesis consist of two parts. In the first part, the finite element code ANSYS is used to simulate the sound radiation of a vibrating plate and sound propagation in open space or a hollow structure. The results of ANSYS are compared with the experimental data obtained in this study. It has been found that the simulation can predict the performance of the speaker well in open space and in muffler as well. In the analysis of sound propagation in pipes, we propose a simplified analytical model using surface impedance to simulate surface sound-absorbing phenomenon of the pipe. The proposed method can effectively reduce the computing time for solving the problem. Compared with the theoretical formula available in the literature, the accuracy of the present finite element model for sound propagation in pipes has been verified by the previous solutions. In the second part, the effects of the pipe geometry and the wall sound absorption coefficient on the noise elimination of the pipes are studied. According to the results obtained in the ANSYS simulation, the parameters of the pipes that can have significant effects on the noise elimination of the pipes are identified.