平面揚聲器中彈性支承的非線性行為研究

Abstract

平面喇叭受彈性支承和音圈的物性與電性影響，聲壓隨著瓦數的增加呈現衰減或扭曲情形，未能把原音完整的表現出來。其中，當彈性支承受到較大的變形量時，由於幾何非線性的影響而產生剛度硬化或軟化現象，以致造成喇叭的非線性衝程。本文將探討不同設計的彈性支承，其中包括接腳與懸邊，而接腳分2-D與3-D兩種。研究如何調整懸邊形狀、尺寸的參數，以提高支承勁度的線性變形量和正反方向的對稱度。首先利用靜力實驗找出各種彈性支承設計的力與位移關係圖，並量測喇叭的聲壓曲線。使用ANSYS建構彈性支承和揚聲板系統的有限單元模型，進行靜力的非線性分析和在線性範圍內的簡諧激震分析。藉比較理論與實驗的結果，以確立支承的材料性質與了解其線性的衝程量。最後分析2-D與3-D接腳搭配懸邊的最佳組合，並由聲壓的實驗與理論值比較得知，最佳的彈性支承可增加聲壓的線性範圍。

Due to the physical and electrical characteristics of flexible supports and voice coil, the Sound Pressure Level (SPL) may behave nonlinearly with the increase of voltage rather than varying linearly. In general, owing to geometric nonlinearity, the rigidity of a flexible support may experience hardening or softening when subjecting large deformation. In this thesis, we discuss several designs of flexible supports including elastic damper (2D or 3D) and suspension. The purpose is to enlarge the range for linear deformation while at the same time maintain the symmetry for positive and negative directions of deformation when designing the elastic dampers and suspension. The goal can be achieved by adjusting the shape and dimension of the flexible supports. First, we find the load-displacement curve of a flexible support via the static experiment, and then we use ANSYS to construct a finite element model of the speaker. Based on the nonlinear deformation and linear harmonic exciting analyses, the SPL curve is obtained and used to verify the results of static and SPL tests so that we can identify the material properties of the supports and find out the linear displacement ranges of the supports. Finally, we use two optimal support combinations including 2-D or 3-D elastic supports and suspension to study the SPL curves of the speaker theoretically and experimentally. The results show that the choices of the optimal flexible supports can produce larger linear range for the SPL curves.