Abstract
A composite structure composed of a porous-material layer mosaicked with a perforated resonator is proposed to improve the low-frequency sound absorption of the porous layer. This structure is investigated in the form of a porous-material matrix (PM) and a perforated resonator (PR), and the PR is a thin perforated plate filled with porous material in its back cavity. Theoretical and numerical models are established to predict the acoustic impedance and sound absorption coefficient of the proposed structure, and two samples made of polyurethane and melamine, respectively, are tested in an impedance tube. The predicted results are consistent with that of the measured. Compared with a single porous layer with the same thickness, the results show that the designed structure provides an additional sound absorption peak at low frequencies. The proposed structure is compact and has an effective absorption bandwidth of more than two octaves especially below the frequency corresponding to 1/4 wavelength. A comparison is also made between the sound absorption coefficients of the proposed structure and a classical micro-perforated plate (MPP), and the results reveal equivalent acoustic performance, suggesting that it can be used as an alternative to the MPP for low–mid frequency sound absorption. Moreover, the influences of the main parameters on the sound absorption coefficient of PPCS are also analyzed, such as the hole diameter, area ratio, flow resistance, and porous-material thickness in the PR. The mechanism of sound absorption is discussed through the surface acoustic impedance and the distributions of particle velocity and sound pressure at several specific frequencies. This work provides a new idea for the applications of the thin porous layer in low- and medium-frequency sound absorption.
Highlights
Porous materials are usually composed of two phases, i.e., solid framework interwoven with pore network, and in the vicinity of the solid–air interface, the sound energy is consumed through viscous dissipation and heat conduction [1–3]
With the development of micro-perforated panels (MPP) theory [8,9], stretched ceilings based on micro-perforated panels [10,11] have been successfully used in room acoustics, and the sound absorption performance of MPP stretched ceilings filled with porous material is better than that of MPP with only air in the cavity
For the serial structure consisting of MPP, airspace, and porous material, Li et al [13] gave a theoretical prediction model with the transfer matrix method, and comparison of different results showed that the sound absorption performance of “porous material–air layer–MPP” is better than that of “MPP–air–porous material”
Summary
Porous materials are usually composed of two phases, i.e., solid framework interwoven with pore network, and in the vicinity of the solid–air interface, the sound energy is consumed through viscous dissipation and heat conduction [1–3]. A structure composed of porous materials and common perforated plate resonators with low perforation rate was designed by Li et al [16] based on the principle of acoustic impedance matching, and an L-shaped cavity was used to provide more compliance This structure with a total thickness of 80 mm has an average absorption coefficient of 0.9 in the frequency range of 200–1600 Hz. Recently, a new concept has been proposed for sound absorptive materials with double porosities. Based on the HPS theory, more double-porosity materials were proposed to improve the sound absorption of conventional porous materials based on the coupling effect of micropores and mesopores, such as slit perforated porous material [21], gradually perforated porous materials [22], porous material with labyrinthine channel [23], and two different micro-porous materials [24] Another type of sound absorption enhancement has a composite structure with resonant inclusions embedded in the porous material matrix [25–33]. The influences of the following parameters are discussed on the sound absorption performance of PPCS: the hole diameter, the area occupancy ratio, the thickness of porous material in the perforated resonator (PR), and flow resistance in the porous material (PM)
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