複合材料板受矩形激震器激震 之揚聲行為研究

Abstract

本文主要探討電磁矩形激震器對於揚聲器聲壓的改良設計。揚聲器為因應現代產品的平面化趨勢，而常將揚聲器製作為狹長型，以增加空間利用彈性。然而一般狹長形揚聲板使用圓形激震器激震時，激震器大小會被揚聲板寬度受限，導致聲壓感度降低及曲線在中音域處附近易有一聲壓落差，影響揚聲器之表現。因此本文使用矩形激震器激震，一方面增加激震器在揚聲板上的激震面積，提升其聲壓感度；另一方面藉改變揚聲板之變形來改善其聲壓曲線。研究方法分為兩部份，第一部份利用有限元素分析軟體ANSYS分析理論聲壓曲線，探討藉由改變揚聲板節線與矩形音圈長短軸比例參數，減緩中音谷之落差；第二部份利用ANSYS分析激震器氣隙磁通密度分布，探討改變激震器之體積與型態等參數，以增加激震力，提升揚聲器之聲壓感度。依以上分析參數結果，歸納出矩形激震器揚聲器之設計準則，再透過揚聲板加勁方式，使聲壓曲線及感度獲得進一步的改善。最後實際製作出揚聲器，並經由實驗驗證，結果顯示其設計準則可平滑矩形激震器激震之聲壓曲線。

This thesis studies the sound radiation of flat-plate loudspeakers using rectangular transducers. Loudspeakers are usually made of long and narrow shape to fit the limited space in slim electronic products. In general, the long rectangular radiating plates are excited by circular transducers for sound radiation. However, the size of the circular transducer is limited by the narrow width of the radiating plate. The small transducer may produce low sound pressure level (SPL) and cause a major dip in mid frequency range. To circumvent the above shortcomings, a rectangular transducer is used to excite the panel for sound radiation. In this way, it increases the stroke of the radiating plate to raise sound pressure. On the other hand, it changes the deflected shape of the radiating plate to improve the SPL curve. The study contains two parts. In first part, the software ANSYS is used to determine the theoretical SPL curve of the plate; the effects of the deflected shape on radiating plate and the aspect ratio of the rectangular voice coil are studied to eliminate any large sound pressure dip on the SPL curve. In the second part, ANSYS is again used to analyze the magnetic flux of a rectangular transducer, the design of the rectangular transducer is modified to increase the Lorentz force for raising the loudspeakers sensitivity. Base on above results, a design procedure is proposed for choosing appropriate panels and transducers that can produce good SPL curves for rectangular speakers. At last, a number of loudspeakers are fabricated and tested to verify the proposed design procedure.