Acoustic Optimization of a Blow Molded Resonant Absorber

Engine compartment closeout panels (belly pans) are an important part of a strategy to reduce exterior vehicle noise. These parts are generally made with a rigid carrier faced on the engine side with an absorbent material (often foam).

Over one year ago these traditional treatments were improved upon by substituting resonant absorbers for the foam. Both the carrier and absorber are now made from a single material and in a one-step manufacturing process. The absorbers are blow molded plate resonators in the shape of “blocks”. Our development target was to work with the manufacturing process to produce a shape that would provide the desired acoustical performance. To do this required two tools.

One tool is a blow molding simulation that describes the manufacturing process that creates the blocks. Another tool is an acoustic simulation that predicts the absorption of the block. By using these two tools it is possible to design a block that can be manufactured in a robust way that will work over a desired frequency range. This development process will be discussed and the practical use of these absorbers will be shown.