Measurement in situ of the absorption coefficient of automobile interior materials based on the pseudo- impedance tube method

How to measure the absorption coefficient of automobile interior materials accurately in situ is a very important issue. The objective of this study was to investigate an experimental method to estimate the absorption coefficient of automobile interior materials in a free-field conditions. Based on the two microphones method (TMM) and the transfer function method (TFM), pseudo-impedance tube method has been introduced to overcome the deficiency of the two methods. In the pseudo-impedance tube method, the impedance tube is used as sound source, and the absorption coefficient is calculated by the TMM. In this paper, simulations of different sound sources directivity characteristic have been presented which demonstrates pseudo-impedance tube is more suitable than the loudspeaker. The absorption coefficients of automobile interior materials samples have been measured by the pseudo-impedance tube method and the TFM. It turned out that results are in good agreement with the ones of the TFM in 500-1000Hz. Therefore, The absorption coefficient of material can be measured with pseudo-impedance tube, this method can effectively make the distance between the signal source and automobile interior materials shorter, and it provides the possibility of measuring the absorption coefficient of automobile interior materials for a small space in situ measurement.