The modified method of measuring the complex transmission coefficient of multilayer acoustical panel in impedance tube

In order to improve the measuring precision of complex transmission coefficients in impedance tube, the influence that comes from the transmission–reflection wave in the transmission tube is analyzed, and the modified formulas of complex reflection and complex transmission coefficients are proposed. With the experiment of organic glass, it can be confirmed that the modified formulas are useful and can decrease the demand of the tube end. Through the measurement of the complex transmission coefficients of multilayer acoustical panel, the complex transmission coefficients of multilayer both forward and backward incidences are definitely the same in theory either normal or oblique incidence. When sound wave is normal incidence, the method is also verified to be correct with experiments in impedance tube.