以互相關檢測理論開發無響室吸音係數測試法之研究－－以多孔性材料為樣本

A Study of Test Method for Absorption Coefficient of Material Through Cross-Correlation in an Anechoic Chamber－ The Porous Plane Materials as Example

本研究以檢討無響室（anechoic chamber）中互相關（cross-correlation）脈衝遲延法檢測吸音率（absorption coefficient）之測試標準為目的，初期實驗試材仍以多孔性材料(porous materials)為樣本。其研究之方法是以M-序列（M-sequence）技術製造擬似白色噪音（white noise)來進行實驗測試，且作為相關函數 （correlationfunction）計算理論之基礎。此法藉由無響室內記錄聲波反射能量，即直達聲（direct sound）與反射聲（reflection sound）之振幅比來推導受測材料之吸音能力（即材料之吸音率）；並調查量測時正確之聲音入射角度與吸音係數之間的關係，以確立互相關脈衝遲延法之實際適用範圍。

The purpose of this study is to research a new absorption coefficientmethod by using correlation technology which has been developed and appliedto the measurement of acoustical qualities. This study employs broadband frequency range 250Hz~4kHz signal – simulated white noise producedby M- sequence technology as the measuring source. The shapes ofthe cross - correlation curves are easy to detect correlation peaks derivedfrom the sound intensity of direct or reflected traces from material withinthe anechoic chamber. They will be proportioned to the ratios of reflectiveenergy as absorption ability or absorption coefficient. Finally, the broadband frequency range, multiple directions for each sound beam can be surveyedindependently to establish a new standard measure for absorptivecharacteristics.