A New Apparatus for Measuring the Effective Coupling of Acoustic Absorption of Materials Used Inside Cabins

The new apparatus developed in this research consists of a measurement tube with circular cross section which is equipped at both ends with sample holders. The sound power is injected by a small aperture on the side and the sound field is captured by a single microphone placed on the side as well. By calculation of the reverberation time inside the tube it is possible to derive the sound absorption coefficient for normal incidence both for a single and for a combination of two test samples. This apparatus is thus suitable to study the acoustic coupling of different types of sound absorbers in order to maximize their effect when used in combination. In the work the theory underlying the measurement method is expounded and the procedure of calculating single and double absorption figures is discussed. A set of experimental data is presented and compared with the available standardized process for the calculation of single absorption values. Then the coupled absorption coefficients are measured and it is shown how the behavior of coupled systems can significantly deviate from the prediction formulas.