具一階剪變形及附加質量複合材料板之振動與聲傳研究

Abstract

本文重點分為兩大部份。第一部份為利用Rayleigh-Ritz method分析揚聲板的振動行為，其中以一階剪變形平板理論模擬揚聲板及利用Timoshenko Beam理論模擬音圈和附加質量。本方法的準確性透過有限單元軟體ANSYS以及實驗的相互驗證，進而簡化模型，節省計算時間，適合做揚聲器的聲傳分析。第二部份為藉由揚聲板附加質量，造成初始共振頻率降低，以增加聲壓曲線的有效頻寬。並利用附加對稱之均布質量來改變揚聲板的節線位置與振形模態，減少音谷的產生及降低音谷落差，其中探討附加質量位置的選擇、附加重量的影響、揚聲板及附加質量的材質對模態及聲壓曲線的影響，設計較佳的參數達到降低音谷落差的目的。

Two parts are discussed in the thesis. The first part is about the construction of the Rayleigh-Ritz method based on the first order shear deformation plate theory and Timoshenko Beam theory for the sound radiation analysis of a flat-panel sound radiator. In the Rayleigh-Ritz method, the voice coil as well as the attached masses of the sound radiator is modeled by Timoshenko beams. The suitability of the proposed method has been validated by the results obtained from the finite element software ANSYS and experiments. The second part is about the study of the effects of the attached masses on the sound radiation behavior of the sound radiator. The purpose of attaching masses onto the sound radiation panel is to lower the resonant frequency of the sound radiator. If the attached masses are situated at inappropriate locations on the panel, unacceptable sound pressure drops may be induced on the sound pressure level (SPL) curve of the sound radiator. Therefore, the finite element method is used to study how the attached masses affect the SPL curve of the sound radiator. Some appropriate locations of the attached masses are determined to improve the smoothness of the SPL curve.