High frequency sound absorption coefficient determination with multi-modal decomposition in improved impedance tube test method

For measuring the sound absorption coefficient in the higher frequency range,multi-modal decomposition method in impedance tube is used to measure material sound absorption coefficient over the cut-off frequency of plane wave in the tube.In the process of measurement,the microphone array is placed along the circumferential and axial directions of the tube,and then decompose the first three acoustic circumferential modes and their axial incident and reflected waves.These measurement data can be used to calculate the material sound absorption efficient up to 10000 Hz.At last the precision of the multi-modal decomposition method is validated by comparing the measurement results of the common impedance tube method.