不同激振位置對條狀複合材料揚聲板揚聲行為影響之研究

Abstract

本文主要探討雙激振系統下聲壓曲線的影響，一方面藉由增加激振器數目提高激振力，提升其聲壓感度；另一方面藉改變雙激振器的激振位置來改善其聲壓曲線的平滑性。研究方法分為三部份，第一部份為用Rayleigh-Ritz method分析揚聲板的振動行為，將揚聲系統簡化成數學模型進行模擬可獲得合理的結果，並可大幅度減少計算時間，在此使用矩形複合材料平板來模擬揚聲板，用彈簧來模擬懸邊，用四根梁來模擬一個音圈，複合材料平板使用古典積層板理論，梁的部分則採用簡易梁理論。首先推導出揚聲板、懸邊及音圈的動能及應變能，用Rayleigh-Ritz method將板及梁之變形以級數方式表示，建立此揚聲系統之總勢位能，並對其變形函數未定係數變分，可求得振動特徵方程式，求解此方程式後可得到板之自然頻率、模態，進而求得聲壓曲線，再將結果與有限元素分析軟體ANSYS及實驗結果相互比較以驗證此種方法的正確性。第二部分利用有限元素分析軟體ANSYS分析各種不同激振位置下的聲壓曲線，並探討聲壓曲線的差異。最後改變揚聲板的材料常數進行聲壓分析，觀察不同材料常數下聲壓曲線的變化，以作為實務上雙激振系統平面揚聲器選擇不同材料揚聲板之參考依據。

This thesis studies the sound radiation of strip-type flat plates excited at different locations. The purpose of exciting the plate at different locations is two-fold: Raise the sound pressure level (SPL) and improve the smoothness of the SPL curve. This study consists of three parts. In the first part, a Rayleigh-Ritz method is constructed to study the vibration of sound radiation plates which comprising a flat plate, a flexible surround, and a number of voice coils. In the mathematical model of the sound radiation plate, the vibration of the plate is formulated on the basis of the classical lamination theory. The flexible surround is treated as spring. The voice coils are modeled by simple beams. The accuracy of the method is verified by the finite element code ANSYS. In the second part, the vibration response of the plate is used in the first Rayleigh integral to construct the SPL curve of the plate. The experimental SPL curves as well as those obtained using ANSYS are used to validate the suitability of the present method for the analysis of sound radiation plates. Finally, the effects of excitation locations on the SPL curves of sound radiation plates are studied. The more appropriate locations of the voice coils are determined to minimize the magnitude of the sound pressure level drop in the mid-frequency range for the plates. The effects of the material constants of the sound radiation plates on the SPL curves are also studied theoretically. The results obtained in this thesis should be useful for the design of flat-panel speakers.