For many years, industries have been searching for effective noise control solutions having cost effective features such as light weight and small volume. Conventional porous acoustical materials such as polymeric fibers, glass fibers and polyurethane foams fall into the category that meet most of these needs, but it is often said that these materials cannot provide effective absorption at low frequencies. Metamaterials or metasurfaces, on the other hand, have become popular recently due to their potential for nearly-perfect low frequency absorption performance. However, these materials still show obvious limitations regarding their implementation in industry due to their weight, volume, manufacturability and cost. So, to provide acoustical solutions that are applicable in automotive and aerospace industries, here we consider modification of sound packages that specifically enhance the low frequency acoustical performance of conventional porous media. It will be shown that by changing the surface treatment of layered sound packages, and by using a combination of limp fibrous and foam-type poro-elastic materials, excellent sound absorption can be achieved in a frequency range from a few hundred Hz to 10000 Hz without a significant weight or volume penalty. The various concepts will be illustrated through example calculations implemented by using a newly-developed transfer matrix method.
Low frequency, Sound absorption, Poro-elastic, Noise control, Layered sound package, Optimization
Acoustics and Noise Control
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