On the in-situ measurement of transmission loss using the local plane wave method

Acoustic transmission loss of partitions can be measured by a two-room method or using a sound intensity technique. In any case, these methods rely on specific sound fields used in the experiment. For instance, the two-room method relies heavily on the diffusivity of the incident sound field, as well as the full absorption in the receiving room. In the actual application in which the partition is used however, the sound field may be very different from the idealized sound fields used in the laboratory experiment. As the acoustic boundary conditions in the sending and the receiving room affects the transmission, a method that shows this dependency would be much more appropriate. The local plane wave (LPW) family of methods have been successfully applied to measure sound absorption [1, 2]. Using the LPW method, one is able to split the total sound field into estimates of the incident field (a wave traveling in one direction) and the reflected field (a wave traveling into the opposite direction). Therefore, as the method does not require any assumptions about the global sound field, it can be used to approximate the sound absorption coefficient of a sample in any practical situation. Based on that very specific feature of the LPW method to separate incoming from reflected sound waves, in this paper, we will demonstrate the ability of the method to measure in-situ transmission loss. The method is explained by means of a numerical (finite element) fluid-structure interaction model.