In-situ measurement of sound absorbing properties using plane-wave sound field reproduced by virtual loudspeaker array

Abstract

A new method of measuring the acoustic properties of sound absorbing material in situ under reproduced plane wave sound field is proposed. This method employs a single loudspeaker to synthesize a virtual array of loudspeakers which reproduce the plane wave sound field in front of the material surface, and applies the standard transfer function method to measure acoustic impedance and absorption coefficient. Simulation shows that this method can accurately measure absorption coefficient in the frequency range of 100–1.6 k Hz. This method is also applied to measure the absorption coefficient and acoustic impedance of two test samples in a semi-anechoic chamber, and compared with two other existing in-situ measurement methods. The proposed method demonstrates higher accuracy in measuring both acoustic impedance and absorption coefficient for the strongly-absorbing material sample in the frequency range of 175–1.6 k Hz and for the weakly-absorbing material sample in the frequency range of 250–1.6 k Hz. Experimental results and theoretical analysis also show that insufficient signal-to-noise ratio and unwanted reflected waves contribute to the insufficient accuracy of this method below 175 Hz.