Frame Resonance of High Air Flow Resistivity Plastic Foams: Properties to Improve Acoustical Absorption of Composite Multi-Layered Systems

The optimization of acoustical properties of multi-layered materials used in the automotive industry requires a good understanding and characterization of the various component layers. This is a particular concern in the case of headliners where performance must be balanced with packing space demands. These composite structures when used with flexible urethane foams provide good stiffness and light weight, but their acoustic performance can be sub-optimal. Measurements undertaken with poro-elastic high airflow resistivity foams highlighted frame resonances which, if exploited, might significantly improve the acoustical performance of this system.

A new modeling technique based on a pseudo-macroscopic description of the poro-elastic material in the framework of a four-pole network will be used to explain these frame resonances. This formulation exploits the electro-acoustical analogy in transmission line theory. The description of the poro-elastic material is based on a global description of the structure superposed on the fluid. Under normal incidence, each phase is assumed to support a compressional wave. In the present study, emphasis will be put on tools to tune these systems to a specific range of frequency and comparison of predictions and measurements will be presented to assess the validity of the modeling technique.