電磁動力式激震器之設計與應用

Abstract

本文主要探討小型(激震器直徑在30 mm以內)電磁動圈式環形激震器的設計，分為外磁式與內磁式兩種結構。根據不同的設計因素，利用有限元素法分析其磁場，得到氣隙磁通密度，進而探討其趨勢。外磁式結構漏磁大，所以也會探討如何改變外磁式結構，使漏磁減至最小而增加氣隙磁通密度。再將分析所得的數據，利用類神經網路建立經驗資料庫，並對網路模擬值、分析值與實際量測值做比較。 之後，將繼續研究激震器的動態行為分析，組合激震器、平面振動板及懸邊形成平面揚聲器進行實驗，量測第一個共振頻率Fs的聲壓與衝程，及系統各個機械性質參數。因為揚聲器在Fs的運動情形為剛體運動，所以我們可以利用一維剛體振動模型模擬，並將模擬的振動量假設為揚聲器的振幅代入簡化後的一維聲壓公式，進而模擬揚聲器的聲壓頻率圖，比較模擬值與實驗值，並探討各個影響因素。量測所得的機械性質參數亦與實際量測值做比較，並探討其誤差因素。

This paper is focused on the design of small circular electrodynamic actuators and the sound pressure simulation of small planar loudspeakers. There are two types of circular electrodynamic actuators which have either an outter magnet or inner magnet. We used 2-D finite element model to analyze the flux distribution in the air gap of the magnet assembly and determine the maximum flux density. Then we studied the effects of different design parameters on the distribution of magnetic flux and used these analytical data together with the neural network method to establish a tool for designing actuators. We made several loudspeakers by assembling actuators , suspensions , and planar vibration plates and measured their amplitudes at the first resonant frequencies Fs and SPL curves. At the first resonant frequency , loudspeaker’s dynamic behavior is same as a one degree of freedom vibration system. Therefore we used a one degree of freedom vitration system to simulate the loudspeaker and caculate the amplitude at Fs. Then we can simulate the SPL curves of loudspeaker by using the one degree of freedom sound pressure theory. We discussed the differences between the theoretical and experimental results and identified the factors which can have influences on the performance of the speakers.