Microperforated Panel Sound Absorber Research Articles

A theoretical study on the effect of a permeable membrane in the air cavity of a double-leaf microperforated panel space sound absorber

A double-leaf microperforated panel absorber (DLMPP) is composed of a two microperforated panel (MPP) with a air cavity in-between, and without any backing structure. It shows a Helmholtz-type resonance peak absorption and additional low frequency absorption, therefore it can be used as a wideband space sound absorber. In this study, a theoretical study is made to examine the effect of a permeable membrane inside the air-cavity. Permeable membranes are studied in our previous studies and proved to be effective to improve the sound absorption performance of various type MPP sound absorbers. We investigate the absorption characteristics of a DLMPP with a permeable membrane in the cavity through numerical examples, and also studied the effect of honeycomb in the cavity of the same sound absorption structure.

Sound absorption characteristics of a double-leaf structure with an MPP and a permeable membrane

As for the sound absorbing system using an MPP (microperforated panel), a double-leaf MPP sound absorber has been studied so far. However, this structure uses two MPPs, which are still expensive, and is disadvantageous when its cost is concerned. Therefore, it is considered that it can be advantageous if one of the leaves can be replaced with a less expensive material keeping high sound absorption performance. In this study, the possibility of producing a useful sound absorbing structure with an MPP and a permeable membrane as an alternative less expensive material is examined. The acoustic properties of this MPP and permeable membrane combination absorber are analysed theoretically with a Helmholtz integral formulation. The absorption performance and mechanism are discussed through the numerical examples. Also, the effect of a honeycomb in the air cavity, which is to be used for reinforcing the structure, is also discussed through a theoretical analysis.

Nested sampling-based design of multilayer microperforated panel sound absorbers

A model-based design approach for microperforated panel absorbers comprised of multiple panel layers is developed. Microperforated panels (MPPs) are becoming increasingly popular as sound absorbers, capable of providing broadband absorption with high absorption coefficients, without the use of traditional porous materials. To increase the bandwidth of the intrinsically peaked narrowband absorption of a single MPP, multiple such panels can be combined into composite sound absorbers. We propose a method based on Bayesian inference to design multilayered MPP absorbers capable of producing a user-specified absorption profile. Using nested sampling to accumulate Bayesian evidence and to implement Occam's razor, the method produces a design requiring the fewest number of MPP layers while meeting the specified design requirements.

(Micro-)Perforated wooden panels as sound absorbers

Different materials have been used as micro-perforated or perforated panels for applications as sound absorbers. The theory of microperforated panel sound absorbers introduced by D.-Y. Maa in 1975 is independent on the material of the panel. So also micro-perforations in wooden panels will give sound absorption. In combination with porous absorbants the efficiency of the absorbers set-ups can be improved. Modern manufacturing tools for wood and wooden veneers allow for perforations of submillimeter diameters of the single pores. Optically these perforations hardly change the impression of the wooden panel. Acoustically the combination of perforated wooden panels and a backing cavity give highly effective sound absorbers. Measured sound absorption coefficients of various set-ups with (micro-)perforated wooden panels will be presented. The new possibilities in design and applications in architectural acoustics will be discussed.

Effect of a honeycomb on the absorption characteristics of double-leaf microperforated panel (MPP) space sound absorbers

Sound absorbers using a microperforated panel (MPP) is usually not strong enough for room interior surfaces because MPPs are in general very thin. In order to solve this weakness, the authors proposed to use a honeycomb attached behind an MPP in the air-back cavity. In the authors previous studies a honeycomb is effective to improve the sound absorption performance of an ordinary wall-backed single-leaf MPP sound absorber. The honeycomb can also be applied to a space sound absorbing structures such as a double-leaf MPP space absorber (DLMPP). In this study, the effect of a honeycomb in the air-cavity on the sound absorption characteristics of a DLMPP is theoretically analysed. In the theory a Helmholtz-Kirchhoff integral formulation is utilised. The theory is validated with experimental results. The effect of the honeycomb on the sound absorption characteristics is discussed through the numerical examples calculated by the present theory. The results show that the honeycomb enhances the resonance peak and shifts it to lower freqeuencies. Although the honeycomb is effective to improve the sound absorption performance of a DLMPP at around resonance peak, it does not affect the additional low frequency absorption which is particular to a DLMPP

Sound Absorption Behavior of Knitted Spacer Fabrics

This paper presents an experimental investigation on the sound absorption behavior of knitted spacer fabrics. Both weft-knitted and warp-knitted fabrics were used in the study due to their different structure features. The weft-knitted spacer fabric used was composed of two varied plain knitted outer layers and one textured polyester multifilament spacer layer, and it was considered as a porous sound absorber. The warp-knitted spacer fabric used was made with mesh structure on the outer layers and monofilament yarn in the spacer layer, and it was considered as microperforated panel sound absorber. The noise absorption coefficients (NACs) of these two kinds of fabrics under both single and multilayer forms as well as their combinations were tested using a two-microphone impedance measurement tube. The results show that the fabric surface structure and thickness, spacer yarn type and their connecting ways, fabric combinations and their arrangement methods have significant effects on the sound absorbability. The results also demonstrate that good sound absorbability could be achieved by using knitted spacer fabrics if suitable fabric structures and combinations are used.