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Porous materials are extensively used in the construction of automotive sound package parts, due to their intrinsic capability of dissipating energy through different mechanisms. The issue related to the optimization of sound package parts (in terms of weight, cost, performances) has led to the need of models suitable for the analysis of porous materials' dynamical behavior and for this, along the years, several analytical and numerical models were proposed, all based on the system of equations initially developed by Biot. In particular, since about 10 years, FE implementations of Biot's system of equations have been available in commercial software programs but their application to sound package parts has been limited to a few isolated cases. This is due, partially at least, to the difficulty of smoothly integrating this type of analyses into the virtual NVH vehicle development.

Due to the pressure on CO₂ reduction, during the last years "lightweight" parts have become rather popular, as opposed to "conventional" parts, traditionally constituted by a heavy mass layer on top of a soft decoupler. While "conventional" parts are based on pure insulation, "lightweight" parts propose some kind of compromise between absorption and insulation. This makes their design difficult: designing a "lightweight" part means adjusting in the proper way the balance between the absorption and the insulation provided by the part itself and the search for an optimal balance has to take into account relevant vehicle-dependent boundary conditions. Typically, in the design of a lightweight dash insulator a key role is played by the presence of the instrumentation panel and by the importance of the pass-throughs. This article describes a procedure that can help the NVH engineer in the above-mentioned task.

The use of small reverberation rooms for the measurement of the Diffuse Field Absorption Coefficient (DFAC) is common practice in the automotive industry. Such practice brings with itself a few issues, related to the limited size of the measurement environment. Some of these issues (e.g. measurements’ repeatability and reproducibility) have already been thoroughly investigated in articles published at past SAE NV Conferences. This paper intends to focus on some other “minor” aspects related to the measurement of DFAC in small reverberation rooms that so far have received little attention but that can, anyhow, have a non-negligible influence on the measurement results, in particular when they have to be compared to target curves.

This article presents a new system for the measurement on small samples of the normal-incidence Insertion Loss (IL) of multilayers used for the manufacturing of automotive sound package parts. The system consists of a rigid piston connected to an electrodynamic shaker and facing a tube positioned just above it. The measurement principle is based on the evaluation of the Transfer Matrix (TM) of the piston-and-sample assembly, from which the desired IL can be calculated. The TM can, in turn, be evaluated from the measurement of the piston velocity and of the acoustic pressure inside the tube, with two different tube termination conditions. The proposed measurement system is first of all aimed at simplifying the assessment of the acoustic insulation of multilayers used for the manufacturing of sound package parts.