Sound absorption of a finite flexible micro-perforated panel backed by an air cavity

Lee, Y.Y.; Lee, Eric Wai Ming; Ng, C.F.

doi:10.1016/j.jsv.2004.11.024

Cited by 161 publications

(94 citation statements)

References 17 publications

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“…They are also widely used in sound absorption applications, as flexible panels covering a porous material [57] or backed by an air cavity [58,59,60]. In such applications, it has been shown that the vibration of the perforated plate has the effect of increasing the absorption coefficient [58]. In developing models for the sound absorption from a perforated plate, the acoustic impedance of a hole was approximated by the analytical solution for wave propagation in a small tube having a circular cross section, as proposed by…”

Section: Perforated Plate Modelsmentioning

confidence: 99%

Sound radiation from perforated plates

Putra

Thompson

2010

Journal of Sound and Vibration

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FACULTY OF ENGINEERING, SCIENCE AND MATHEMATICS INSTITUTE OF SOUND AND VIBRATION RESEARCH Doctor of Philosophy SOUND RADIATION FROM PERFORATED PLATES by Azma PutraPerforated plates are quite often used as a means of engineering noise control to reduce the sound radiated by structures. However, there appears to be a lack of representative models to determine the sound radiation from a perforated plate. The aim of this thesis is to develop such a model that can be used to give quantitative guidance corresponding to the design and effectiveness of this noise control measure.Following an assessment of various models for the radiation efficiency of an unbaffled plate, Laulagnet's model is implemented. Results are calculated and compared with those for baffled plates. From this, simple empirical formulae are developed and give a very good agreement with the analytical result. Laulagnet's model is then modified to include the effect of perforation in terms of a continuously distributed surface impedance to represent the holes. This produces a model for the sound radiation from a perforated unbaffled plate. It is found that the radiation efficiency reduces as the perforation ratio increases or as the hole size reduces. An approximate formula for the effect of perforation is proposed which shows a good agreement with the analytical calculation up to half the critical frequency. This could be used for an engineering application to predict the noise reduction due to perforation.The calculation for guided-guided boundary conditions shows that the radiation efficiency of an unbaffled plate is not sensitive to the edge conditions. It is also shown that perforation changes the plate bending stiffness and mass and hence increases the plate vibration.The situation is also considered in which a perforated unbaffled plate is located close to a reflecting rigid surface. This is established by modifying the Green's function in the perforated unbaffled model to include an imaginary source to represent the reflected sound. The result shows that the presence of the rigid surface reduces the radiation efficiency at low frequencies.The limitation of the assumption of a continuous acoustic impedance is investigated using a model of discrete sources. The perforated plate is discretised into elementary sources representing the plate and also the holes. It is found that the uniform surface impedance is only valid if the hole distance is less than an acoustic wavelength for a vibrating rectangular piston and less than half an acoustic wavelength for a rectangular plate in bending vibration. Otherwise, the array of holes is no longer effective to reduce the sound radiation.Experimental validation is conducted using a reciprocity technique. A good agreement is achieved between the measured results and the theoretical calculation for both the unbaffled perforated plate and the perforated plate near a rigid surface.

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Section: Perforated Plate Modelsmentioning

confidence: 99%

Sound radiation from perforated plates

Putra

Thompson

2010

Journal of Sound and Vibration

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“…These values correspond precisely to results that can be obtained using the equations presented in Section 2. The small peak at about 850 Hz for the cavity depth of 10 mm is believed to be the result of the panel vibration as reported in [17][18][19][20][21]. The measurements for all other types of MPPs showed the same trend, and are therefore not presented in this report.…”

Section: Measurementsmentioning

confidence: 74%

“…As reported by Lee et al [17] and also in [18][19][20][21], the vibration of the panel can affect the value of sound absorption coefficient significantly. The effect was reported to be particularly strong around the resonance frequencies of the panel.…”

Section: Measurementsmentioning

confidence: 85%

An Experimental Study of a Multi-Size Microperforated Panel Absorber

Miasa

Okuma

Kishimoto

et al. 2007

JSDD

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A new type of microperforated panel absorber (MPA) that has holes of multiple sizes instead of uniform size is experimentally investigated. The objective of this research is to obtain a wide band sound absorber that is thin, durable, clean, and healthy. The first step of this research is to investigate the performance of MPA having two different sizes and the same numbers of holes. The investigation is then extended to a combination of three and four different sizes of holes with various spatial arrangements and various densities or percentages of each size of holes on panels. The hole diameters vary between 0.4 mm and 1 mm and the cavity depths vary between 10 mm and 15 mm. The results show that a multi-size MPA enhances the absorption rate and widens the effective frequency band. This study also proves that a multi-size MPA when compared with a uniform size MPA has better sound absorption characteristics with respect to the absorber thickness and absorption bandwidth. These results make it possible to build thin, single layer sound absorbers that are effective in wide frequency bands and have the advantage of being tunable.

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“…The discrepancy of the Maa model results and the measurement ones are around 4% up to 14 % at half absorption frequency range. Some peaks are also present that are related with the panel resonances [19,20]. Those peaks are not considered in the Maa model so they are missing from the predicted results.…”

Section: Effect Of Panel Thicknessmentioning

confidence: 99%

Study on inhomogeneous perforation thick micro-perforated panel sound absorbers

Prasetiyo¹,

Sarwono²,

Sihar³

2016

J. MECH. ENG. SCI.

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Micro-perforated panel (MPP) sound absorbers are usually made of a thin panel and have narrow absorption bandwidth. This drawback causes the application of MPP to be limited. In this paper, the possibility of realizing wider absorption bandwidth MPP with sufficient structural strength is investigated. For this, multi-MPP (resonator) arranged in parallel to form an inhomogeneous perforation MPP is introduced to widen the absorption bandwidth. The thickness of MPP must be 1.5 times higher than perforation diameter or more in order to have appropriate strength. The characteristics of corresponding absorption coefficients are studied parametrically using theoretical models as thick panels can reduce the MPP's performance. It is found that the absorption bandwidth of thicker panels with inhomogeneous perforation approach can be at least twice times of classical MPP. The problem of reduced peak absorption coefficient in a thick panel can be avoided by keeping the acoustic resistance value around 1± 0.5 Rayls. Compared with homogeneous MPP, inter-resonator interaction exists in the inhomogeneous perforation thick MPP that causes the overall absorption to become higher due to the increasing of the acoustic resistance as well as the shifting of peak resonance following residual acoustic reactance. The measurement results confirm all of the characteristics.

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Sound absorption of a finite flexible micro-perforated panel backed by an air cavity

Cited by 161 publications

References 17 publications

Sound radiation from perforated plates

Sound radiation from perforated plates

An Experimental Study of a Multi-Size Microperforated Panel Absorber

Study on inhomogeneous perforation thick micro-perforated panel sound absorbers

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