矩形揚聲板受不同激振方式之最佳化設計

Abstract

平面揚聲器在中音域附近易有一聲壓落差，稱為音谷，音谷的產生會影響揚聲器表現。因此本文利用附加對稱質量及改變激振方法改善聲壓曲線，減少音谷產生。以古典板理論及Rayleigh-Ritz數值方法結合總域極小值最佳化理論設計附加對稱位置質量的最佳位置，探討碳纖揚聲板附加質量對聲壓曲線及振動模態之影響，達到欲改善的聲壓區間曲線平滑，且探討該質量位置對振動模態之影響。本文亦研究片狀激振器之製作，此新型之激振器可隨意更改激振方式與位置，在揚聲器的研製上可有相當大的應用，以最佳化方法找出最佳之激振位置，另依分析的結果實際製作出揚聲器並量測其聲壓曲線，結果顯示其確有較平滑的聲壓曲線表現。 本文歸納出可依據不同尺寸之揚聲板選擇適當的方法改善聲壓曲線。

Panel-speakers may have dips in mid frequency range on the sound pressure level (SPL) curve. In general, such dip can be harmful to the sound quality of the loudspeakers. In this thesis, the mid-frequency SPL dips are suppressed or eliminated using two different methods. In the first methods, point or distributed masses are attached to the plate at different locations to improve the smoothness of the SPL curve in a specific frequency range. An optimal design method is used to determine the locations of the masses. In the optimal design process, the vibration analysis of the sound radiation plate is accomplished using the Rayleigh-Ritz method, the sound pressure produced by the sound radiation plate is calculated using the first Rayleigh integral, and the optimal excitation location is determined using a global optimization technique. In the second method, the K-exciter is used to excite the sound radiation plate. The advantages of K-exciter are that it can be put anywhere on the plate and the shape of excitation force can be in any form. The optimal excitation locations are obtained in the optimal design. The feasibility and applications of the proposed methods have been validated by experimental results.