Structure Borne Insertion Loss of Sound Package Components

Typical automotive sound package components are usually characterized by their absorption coefficients and their acoustic power-based insertion loss. This insertion loss (IL) is usually obtained by subtracting the transmission loss (TL) of a bare flat steel plate from the TL of the same plate covered with the trim material. While providing useful information regarding the performance of the component, air-borne insertion loss is based solely on acoustic excitations and thus provides very little information about the structure-borne performance of the component.

This paper presents an attempt to introduce a standard procedure to define the power-based structure-borne insertion loss of sound package components. A flat steel plate is excited mechanically using a shaker. Different carpet constructions are applied on the plate and tested. Based on velocity measurements, a force transducer and intensity probe, the mechanical input and the acoustic radiated power are obtained. Structure-borne insertion loss is then calculated from the input and radiated power measurements. Details of the technique are described and results for different configurations are presented and discussed. In order to analyze the governing physical mechanisms, low and high frequency numerical simulations are studied. The numerical approach is based on two methods;1) the low frequency spectrum is covered using a finite element formulation,2) a transfer matrix approach, modified to incorporate mechanical excitations, is used for the high frequency portion of the spectrum.