2018 Volume 39 Issue 6 Pages 417-423
To measure the normal incident sound absorption coefficient and transmission loss for frequencies around 10 kHz, a small impedance tube with an inner diameter of 15 mm was developed. It was found that the influences of sound attenuation, caused by the viscosity of air near the inner tube wall and the surface roughness on the wall of the tube at microphone, were non-negligible. To address these issues, we propose a correction method for the sound attenuation and an improved microphone holder to smoothen the inner wall surface. It was then possible to accurately measure the sound absorption coefficient and transmission loss with acceptable level of accuracy.