傳輸矩陣法在微穿孔板以及穿孔板背貼多孔性吸音材之吸音特性應用

Abstract

本文目的在探討改變穿孔直徑、穿孔率、背後空氣層厚度以及背貼材料厚度和不同材料的流動阻率時，微穿孔板以及穿孔板背貼多孔性吸音材料之吸音效果。為了分析此兩種吸音結構的吸音理論，結合聲波在不同介質的傳輸矩陣，得到材料表面阻抗及吸音率的計算公式，並在阻抗管中進行實驗，結果理論計算和實驗结果符合良好，最後再從理論上，改變上述結構參數，以計算其對吸音率的影響。 本研究所得之結論有以下幾點： 一、 對微穿孔板設計而言，針對低頻及吸收頻寬，孔徑0.4mm、穿孔 率1％、板厚1mm以及較大的空氣層厚度會有較佳的吸音率。 二、雙層比單層微穿孔板結構在低頻吸音效果更好且吸收頻寬更大。 三、對於穿孔板背貼多孔性吸音材料，因為多孔性吸音材料在高頻的 吸音率較好，所以適當地調整孔徑、穿孔率等結構參數，可使吸音結構在高低頻皆能有理想的吸音率。 四、背貼吸音材時，穿孔板的穿孔率要大於20％以上時，吸音才有一 定效果。 五、微穿孔板的聲學特性是由板本身的結構參數所決定；穿孔板孔徑 較大且當穿孔率大於20％，聲學特性主要由空腔内的吸音材料决定。

This study is mainly to discuss the sound absorption effects of mirco-perforated panels and perforated panels backing with porous materials when changing the diameters of the apertures,the perforation,the thickness of air layers,the thickness of backing materials and the flow resistivities of different materials.In order to analyze these two absorptive structures,assocating the transfer matrices of sound wave in different media,and we can get the formulas of surface impedances and sound absorption coefficients,and then we do experiments in the impenance tubes.It shows that the theory and the experiment result can match well. Finally, we change parameters of the sound absorptive structers and calculating the influence of the sound absorption coefficients from the theory. There are some conclusions as follow: 1.For designing mirco-perforated panels,the diameter is 0.4mm,the perforation is 1％,the panel thickness is 1mm,and the larger air layer will get advance in sound absorption coefficients in low frequency and sound absorption bandwidth. 2.The double layer of the mirco-perforated panels will have better sound absorption effects and can broaden the frequency range of sound absorption. 3.For perforated panels backing with porous materials,because the porous materials have higher sound absorption coefficient in high frequency,we can adjust the structure parameter,ex: the diameters of the apertures,the perforation...etc,that can make structures have ideal sound absorption effects in both low and high frequency. 4.The perforation must be over 20％, and then the sound absorption have some level effect when perforated panels backing with porous materials. 5.The acoustic characteristic of the mirco-perforated panels is decided by the structure parameters of panels themselves,and when the diameters of the apertures are larger and over 20％, the acoustic characteristic is decided by the absorptive materials in air layer.