Since the concept of microperforated panels (MPPs) was introduced by Maa, there have been continuing efforts to apply MPPs, primarily as fiber-free sound absorbing materials, typically wall-mounted. The objective of the present work was to demonstrate that multi-layer MPPs can also be effective functional absorbers and lightweight barrier systems. The acoustical properties of lightweight MPPs depend on hole diameter, thickness, porosity, mass per unit area, and air cavity depth. In the case of a single layer, it is possible to find a combination of these parameters that results in good performance over one or two octaves. However, to be effective for noise control over a broader range of frequencies, it is necessary to design multi-layer MPPs. Thus here the focus was on the optimal design of multi-layer MPPs in the speech interference range, 500 to 4000 kHz. In the case of functional absorbers, the total absorption of the system was optimized, while in the case of barriers, a high transmission loss was desired, without necessarily sacrificing the absorption of the system. In the latter case, in particular, it was possible to create systems having transmission losses well in excess of the mass law over a broad range of frequencies.
Microperforated panels, Sound transmission, Barriers, Functional absorbers, Multiple layers
Acoustics and Noise Control
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