An Intensity Method for Measuring Absorption Properties in situ

The well-known Kundt's tube and reverberant room method are often used for measurement of acoustic absorption properties of samples under laboratory conditions. Several in situ measurement methods exist, but most of them are limited in frequency range, require large samples and/or are vulnerable to background noise or reflections. The PU in situ impedance method [1, 2] has been used successfully on relatively small samples (> 0.1 m2) in a broad frequency range (300 Hz - 10 kHz) under reverberant conditions (e.g. a car interior or a concert hall), see e.g. [3, 4, 5, 6, 7]. The small source-sample and probe-sample distance are the main reasons for the relative small sample size requirement and the low influence to background noise and reflections. However, in some cases the procedure shows artefacts because all the reflection at the top of the sample is considered, not taking into account wave propagation in the material. In this research the principle of measuring intensity instead of impedance is investigated. To eliminate near field effects an extrapolation technique is introduced that combines several measurements. The result is a technique to measure the absorption coefficient without knowledge of the material. The methods are examined theoretically and verified with experiments. References: 3 references open in new window Articles that cite this article?