In situ impulse response method of oblique incidence sound absorption coefficient with microphone array

Abstract

The paper reports the development of the methods for measuring oblique incidence sound absorption coefficient in situ. The standing wave tube method and reverberation room method are not suitable for the test in situ. And the transfer function method presented by Allard fails to consider scattering effect of unsmooth surfaces. Based on the use of microphone array, the paper presents an impulse response method to study oblique incidence sound absorption coefficient. The impulse signal generator is designed to simulate pseudo-random noise including many different frequencies. The microphone array can eliminate the effect of reflection and scattering. The paper compares the impulse response methods of in situ measurement in reverberation room and free field, with another method which used in standing wave tube. The specimen is made of polyurethane foam. The results show that the absorption coefficient obtained by the standing wave tube is similar to reverberation room, but smaller than free field. Although the results obtained by three methods are not the same, the three curves reflect the same varying tendency. This in situ method can satisfy the technical requirement of measuring.