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The need for the industry to simulate and optimize the acoustic trim parts has increased during the last decade. There are many approaches to integrate the effect of an acoustic trim in a finite element model. These approaches can be very simple and empirical like the classical non-structural mass (NSM) combined to a high acoustic damping value in the receiver cavity to much more detailed and complex approach like the Poro-Elastic Materials (PEM) method using the Biot parameters. The objective of this paper is to identify which approach is the most appropriate in given situations. This article will first make a review of the theory behind the different methods (NSM, Impedances, Transfer Matrix Method, PEM). Each of them will be investigated for the different typical trim families used in the automotive industry: absorber, spring/mass, spring/mass/absorber.

The need in the automotive industry to understand the physical behavior of trims used in a vehicle is high. The PEM (poro-elastic method) was developed to permit an explicit representation of the trims in the FEM full vehicle models and to give tools to diagnose the effect of the trims and test design changes (porous material property, geometry, etc.,). During the last decade, the evolution of software and hardware has allowed the creation of models with highly detailed trim description (porous material using Biot parameters, plastic trims, etc.,). These models can provide good correlation up to 400Hz compared to measurements in contrast to classical NSM (Non Structural Mass) methodology which shows limitations.