Improvement Of Interior Acoustics Of A Top-class Car In The Low Frequency Range Using A Hybrid Numerical-experimental Technique

Numerical prediction plays a key role during the development of new car projects, and definition of dynamic-acoustic behaviour of sound proofing materials is a crucial task in this process, in order to optimize the final noise as well as the weight of the vehicle treatment. Inside the development of a new project, the well-known FSI (Fluid-Structure Interaction) technique, based on FEM models of both car body and cavity has been succesfully applied since the last ten years, but in this simulation system acoustic materials have been taken into account only as acoustic impedances, representing a boundary condition for the fluid-structure interaction. This paper would like to represent a step ahead in material simulation, where Uhe dynamic behaviour of the various panels composing the car body are calculated in complete models (sheet metal layer+damping layer+sound insulating layer), separately from the "treated" cavity. The cavity behaviour is taken into account experimentally, measuring the acoustic transfer functions between panels and reference microphones, and these results are finally merged with velocity profiles coming from FEM simulation of complete panels to achieve a final noise prediction. An application of this technique to a top-class car acoustics is discussed, reviewing the various steps of the simulation and measurement processes and evaluating the various proposed alternatives for the acoustic treatment and their effects in the lowfrequency band (typically the 2nd firing order), with also a final comparison with a real testbench measurement on the car prototype.