平板揚聲器之設計與失真研究

Abstract

本文採用無彈波並且以結構性支承取代傳統懸邊支承的設計，以及不同的碳纖肋條加勁複材三明治板，實際製作研發一新型之全音域長方形平板揚聲器，並比較各種支承的優缺點。介紹各種不同形式的失真並以諧波失真為主要探討對象。以數學的方式說明諧波失真如何產生，以及奇次諧波大於偶次諧波的原因。探討驅動力與懸邊勁度非線性對低頻失真的影響。探討中高頻失真與共振頻率及最大失真頻率與中音谷關係。討論揚聲器各項參數對失真曲線的影響，以及降低失真的可行方法。探討現行的諧波失真量測誤差來源，並以雷射測位儀所測得的位移失真與麥克風所測得的聲壓失真比較。

An innovative design of flat panel loudspeaker is proposed, which adopts no spider and uses structural supports instead of conventional suspension. Different reinforced composite sandwich panels are fabricated and used to make a rectangular flat panel loudspeaker with frequency response range from 120Hz to 20kHz. Harmonic distortions of the flat-panel speakers are measured to study the cause of the distortions. The influences of the nonlinearity of motor force and suspension stiffness on low frequency distortion are investigated and the relation between the mid-frequency-dip and mode shape and the cause of distortion in mid-frequency range are also studied. The displacement distortion recorded from LDV(Laser Doppler Velocimeter) and the sound pressure distortion measured by microphone are used to study the sources of measurement inaccuracy.