Validation study of in situ sound absorption measurement

An in situ acoustic tube measurement is a non-destructive way to measure the sound absorption coefficient of a material. This method is practical for obtaining sound absorption in cases where it is not straightforward to sample specimens in applications such as automobile interiors, room walls, ceilings, or carpeted floors. However, the in-situ method's limitations lie in measurement errors due to the sound energy leakage through the open boundaries within the materials. In addition, it is not straightforward to provide a general correction factor compared to the standard in-tube method because the errors depend on various factors such as material characteristics, material flow resistance, installation conditions, pipe flange size, etc. The aim here is to provide practical guidelines for reducing in-situ error by analyzing and comparing that procedure with the standard in-tube method. Here, in-tube and in-situ methods were used to measure and they were then analyzed by creating FEM-based acoustic tube and poro-elastic material models. The effect of material flow resistivity and flange thickness were investigated and reported.