Sound absorption and transmission through flexible micro-perforated panels backed by an air layer and a thin plate

Abstract

This paper describes theoretical and experimental investigations into the sound absorption and transmission properties of micro-perforated panels (MPP) backed by an air cavity and a thin plate. A fully coupled modal approach is proposed to calculate the absorption coefficient and the transmission loss of finite-sized micro-perforated panels-cavity-panel (MPPCP) partitions with conservative boundary conditions. It is validated against infinite partition models and experimental data. A practical methodology is proposed using collocated pressure-velocity sensors to evaluate in an anechoic environment the transmission and absorption properties of conventional MPPCPs. Results show under which conditions edge scattering effects should be accounted for at low frequencies. Coupled mode analysis is also performed and analytical approximations are derived from the resonance frequencies and mode shapes of a flexible MPPCP. It is found that the Helmholtz-type resonance frequency is deduced from the one associated to the rigidly backed MPPCP absorber shifted up by the mass-air mass resonance of the flexible non-perforated double-panel. Moreover, it is shown analytically and experimentally that the absorption mechanisms at the resonances are governed by a large air-frame relative velocity over the MPP surface, with either in-phase or out-of-phase relationships, depending on the MPPCP parameters.

Enhancing sound absorption and transmission through flexible multi-layer micro-perforated structures

“…a À s, calculated from Eqs. (14) and (15), represents the fraction of incident power dissipated in the ML-MPP.…”

Modeling vibroacoustic systems involving cascade open cavities and micro-perforated panels

“…[15][16][17] Therefore, an accurate description of the MPP inside complex vibroacoustic environment requires the inclusion of MPP vibration.…”

“…1 is considered here, in which staggered partial partitions or MPPs are connected in cascade through open acoustic cavities. The system can actually represent a wide range of practical applications, such as MPP backed by air layer and flexible plate, 16 double-glazed ventilation window 27 and with MPP absorbers, 13 allowing a flexible description of the separation layers. In the inlet duct, the system is excited by a normal incident plane wave.…”

“…Because of its appealing features such as cleanable, fiber-free and noncombustible, MPPs have found their use in a wide range of practical applications. [13][14][15][16][17][18][19][20] For example, Kang and Brocklesby 13 investigated the feasibility of applying MPP absorbers in ventilated window system. Allam and Å bom 14 proposed a new type of silencer based on MPP with slit holes.…”

“…Wang et al 15 developed a hybrid silencer using lightweight MPPs coupled with side-branch cavities. Bravo et al 16,17 discussed the sound absorption and transmission of flexible MPPs and MPPs backed by a flexible plate. Liu and Herrin 18 studied the effect of MPP absorption in acoustic enclosure by partitioning the backing cavity.…”