Abstract
Sound absorbing materials are used in buildings to dissipate sound energy into heat using viscous and thermal processes. Sound absorbers increase the transmission loss of walls, decrease the reverberation time of rooms, and attenuate the noise generated by internal sound sources. Porous absorbers (fibrous, cellular, or granular) are the most used materials in noise control applications because of their high performance-to-cost ratio in the frequency band of interest. However, when cleaning conditions and health reasons are of concern, microperforated panel (MPP) absorbers may be the preferred choice. MPPs, consisting of many minute (sub-millimetric) holes in a panel, are tunable absorbers in a prescribed frequency band, whose main shortcomings are high manufacturing cost and limited absorption frequency band. Currently, the production cost of MPPs can be drastically reduced by means of modern techniques. The absorption frequency band can be considerably enlarged by designing multiple-layer MPPs (ML-MPPs). The aim of this article is to review the high potential of ML-MPPs as a modern, clean, and healthy alternative to porous materials for sound absorption.
Highlights
Porous and fibrous materials are excellent sound absorbers available at a reasonable cost
The absorption frequency band can be considerably enlarged by designing multiple-layer microperforated panel (MPP) (ML-MPPs)
The aim of this article is to review the high potential of ML-MPPs as a modern, clean, and healthy alternative to porous materials for sound absorption
Summary
Porous and fibrous materials are excellent sound absorbers available at a reasonable cost. Porous and fibrous absorbers can potentially release particles which can become problematic in environments requiring special cleaning and health conditions, such as the food industry, hospitals, or white rooms for the production of microelectronic devices Other applications where these materials are not recommended are the inside of ducts where high velocity gases circulate, such as the exhaust of engines [1]. The MPPs formerly proposed by Maa consisted of a distribution of minute circular holes of diameter d, over a panel of thickness t, with a perforation ratio, or porosity, φ. This MPP has an acoustic impedance, Z, which is complex (i.e., it has resistive and reactive components). A single-layer MPP (SL-MPP) is obtained which depends on the parameter set (d,t,φ,D)
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