Sound Insulation Provided by a Multi-layer System Containing a Heterogeneity: a BEM Approach

The sound insulation provided by a multi-layer partition with an infinite plane, composed of sets of fluid and elastic layers, dividing an infinite acoustic medium is analysed in this paper. A circular cylindrical fluid-filled heterogeneity is placed inside one of the elastic layers of the partition and the resulting airborne sound insulation and the impact sound pressure level are calculated. The solution is obtained using a Boundary Element Method (BEM) formulation in the frequency domain, where only the discretization of the heterogeneity’s surface is required, since Green’s functions are used for the multi-layered media. The model is excited by cylindrical line loads placed in either the acoustic or the elastic medium. Material losses are taken into account by means of complex velocities. A similar model has been developed by the authors in previous work, in that case to predict the sound insulation provided by single partitions in the presence of rigid, free, fluid-filled and elastic-filled heterogeneities. It is extended here to handle multi-layer systems. Several simulations are performed to see if the presence of fittings such as pipes, which are often housed inside building partitions, may affect the sound insulation. The analysis assumes multi-layer partitions, such as those built with two elastic layers sandwiching an air gap, and floating systems composed of a concrete screed resting on a cork layer laid over a structural concrete layer. An air-filled heterogeneity is placed inside one of the elastic layers. Responses are compared with those provided by the solution without the presence of the heterogeneity. The analysis allows the conclusion that the sound insulation is slightly affected by the presence of the heterogeneities inside multi-layer systems.