振膜材質組合對微型揚聲器輸出影響探討

Abstract

本研究將利用有限元素法模擬微型揚聲器受力時的運動形態，進而計算出揚聲器系統的頻率響應曲線。首先會探討音圈位置對於整體聲壓造成的影響，由於振膜改進設計主要是希望可以擴大頻率範圍，即第一個模態頻率降低、第二個模態頻率提高，同時增加整體聲壓輸出並使整體聲壓較為穩定。 經由討論音圈位置，發現音圈半徑的大小對於模態頻率的影響甚大；基本上揚聲器第二個模態形狀可以分為音圈內及音圈外的振膜振動，所以本研究將針對這兩種情形做振膜材質的探討，藉由振膜材質改變進行相關討論，找出增加揚聲器效能的方法。 本論文經由軟體模擬後發現，當第二個模態形狀主要為音圈以內振膜運動時，因為第一個模態與第二個模態運動的位置不同，所以較容易以振模材質改變的方式進行振膜改進設計，即可以分別改變音圈內外材質使第一個模態頻率與第二個模態頻率間的間距增加。並發現當第二個模態形狀主要為音圈以內運動時，模態頻率改善的情形較佳，所以討論振膜厚度時，本論文將以第二個模態形狀為音圈以內運動之模型進行討論，此時，可以得到振膜厚度與第一個模態頻率成等比成長。 而有限元素法模擬微型揚聲器相較於電機聲等效電路，雖然計算量較大，但對於高頻部分可以有效描述，有利於改進整體揚聲器系統之精確度。

In this thesis, the use of the finite element method is to simulate the micro-speaker and then calculate the sound pressure level of the speaker system. First, this study investigates how the voice coil positions impact on the overall sound pressure. The improved design of diaphragm is hoping to reduce the first eigen frequency and elevate the second modal frequency to increase the overall sound pressure and that the overall sound pressure can also be more stable. Through the discussion to the position of the voice coil, the radius size of the voice coil has great influence to the sound pressure level. Basically, the speaker’s second mode shape can be divided into voice coil inside and outside diaphragm vibration. With this reason, the investigation of the diaphragm material will base on these two cases and find out the way to improve the efficiency of the speaker by changing the membrane material. In this thesis, after simulation by software, it is found that when the second mode shape is in motion as voice coil inside diaphragm, it is easier to improve the design by changing the diaphragm’s material, due to the first and second mode shape are in different positions of motion. That means the spacing between first and second frequency can be elevated by replacing the material of the voice coil inside and outside. So we will use this model when discussing the thickness of diaphragm, and will get the result that the first eigen frequency will proportional to the thickness of diaphragm. The finite element method is more efficient and accurate than the electro-mechano-acoustic analogous circuits, although the finite element method has larger amount of calculation, but could effectively describe the high frequency portion and well improved the overall accuracy of the speaker system.