In previous work, a sound package consisting of a layer of limp, fibrous material and a flexible microperforated panel was considered. It was found that a weight optimization process for their treatment gave many different flow resistivity and surface density combinations that yielded the same spaceaveraged interior pressures downstream of the sound package. Thus, from the optimization results, it was possible to identify a potential weight reduction range. Generally, it was found that a combination of a relatively heavy, high flow resistance MPP with a relatively light fibrous layer gave the lowest weight solutions at a given space-average pressure (SAP) for this particular sound package configuration when mounted to a 1 mm aluminum panel. Note, however, that exterior noise transmits into a vehicle’s interior by many different paths, and air leaks that form in the dashpanel, for example, are particularly important. Therefore, the impact of leaks on the performance of sound packages needs to be considered when it comes to weight optimization. In particular, a small amount of leakage can significantly degrade the transmission performance of a treatment. In the present work, air leakage was modeled as a parallel path through the sound package. Further, to identify the effect of a heavier rigid panel on the optimization results, the aluminum panel was replaced by a 1 mm steel panel. Finally, in order to see the effect of the interior absorptivity of the cabin on the weight resulting from the sound package optimization, the calculation of the aluminum, no-leakage case was repeated with reduced interior absorption.
Sound transmission, Sound absorption, Automotive sound package, Weight minimization
Acoustics and Noise Control
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