Space Sound Absorbers Research Articles

Influence of the acoustic structures placement on the measurements in a reverberation room

Absorption coefficient is a signification index of acoustic structures, which is useful to determine acoustic treatment with a good sound-absorbing characteristic. To make the sound absorption of acoustic structures measured in a reverberation room more closely approximates the sound absorption that would be performed under the applicational condition, this paper studies the influence of different placements on the measurements in the reverberation room. In this paper, the absorption coefficients of micro-perforated membrane and micro-perforated stretch ceiling space sound absorbers are measured, which are placing in the middle of the reverberation room, close to the side walls of the reverberation room and in the corner of the reverberation room respectively. The experiments show that different placements of acoustic material in reverberation room have obvious effect on sound absorption above the 500Hz. It is more efficient to place materials in the middle of the reverberation room, while the absorption of being close to the side walls or in the corner of the reverberation room weakens. The results were agreed with the measurement of micro-perforated stretch ceiling space sound absorbers. It is useful to optimize the arrangement of acoustic materials and structures in controlling the building and rooms noise.

Application of Paper Folding Technique to Three-Dimensional Space Sound Absorber with Permeable Membrane: Case Studies of Trial Productions

The authors propose a space sound absorber made of a permeable membrane (PM), including woven or non-woven fabrics in three-dimensional shapes, e.g., cylinder, rectangle, etc. The proposed absorbers are examined by experimental measurements and boundary element analyses, and it is found that they can be effectively used especially for middle and high frequencies. In order to develop these absorbers for wider applications, it would be desirable to give them additional values and functions, particularly to elaborate on their design. Supposing that they could also be used for lighting equipment, such as lampshades as one of the applications, pilot studies on pseudo-cylindrical, and pseudo-spherical PM space absorbers with uneven surfaces produced by paper-folding (origami technique) are carried out. The pseudo-cylindrical concave curves (PCCC) shell shape has been proven as a suitable form for a lampshade, and the pseudo-spherical concave curves (PSCC) shell shape is an application of PCCC. In this paper, PCCC and PSCC shell shapes are applied to three-dimensional PM space absorbers, and trials are conducted using PMs selected by flow resistance measurements and preliminary simulations. The sound absorptivity of the specimens is measured in a reverberation chamber, and their absorptivity is 0.6 (PCCC case) and 0.4 (PSCC case) at mid-high frequencies.

Some considerations on the use of space sound absorbers with next-generation materials reflecting COVID situations in Japan: additional sound absorption for post-pandemic challenges in indoor acoustic environments

In this study, we first point out the possible acoustic problems associated with the post-pandemic operation of built environments. In particular, we focus on the problem of acoustic deficiency due to the lack of absorption. This deficiency, which is likely to be encountered in most enclosed spaces in a range of establishments, is due to the reduced number of audience members or users of the space as a result of social distancing. As one of the promising solutions to this problem, we introduce a sound absorption technique using three-dimensional (3D) space sound absorbers developed through our recent research projects. Significantly, the type of sound absorber proposed herein is made of materials that are especially suited to hygiene considerations. The materials are microperforated panels (MPPs) and permeable membranes (PMs), both of which are easily washable and sanitised. Furthermore, we point out that 3D-MPP or PM space absorbers possess the additional value of aesthetic designability.

Predicted Absorption Performance of Cylindrical and Rectangular Permeable Membrane Space Sound Absorbers Using the Three-Dimensional Boundary Element Method

Three-dimensional, permeable membrane space sound absorbers have been proposed as practical and economical alternatives to three-dimensional, microperforated panel space sound absorbers. Previously, the sound absorption characteristics of a three-dimensional, permeable membrane space sound absorber were predicted using the two-dimensional boundary element method, but the prediction accuracy was impractical. Herein, a more accurate prediction method is proposed using the three-dimensional boundary element method. In the three-dimensional analysis, incident waves from the elevation angle direction and reflected waves from the floor are considered, using the mirror image. In addition, the dissipated energy ratio is calculated based on the sound absorption of a surface with a unit sound absorption power. To validate the three-dimensional numerical method, and to estimate the improvement in prediction accuracy, the results are compared with those of the measurements and two-dimensional analysis. For cylindrical and rectangular space sound absorbers, three-dimensional analysis provides a significantly improved prediction accuracy for any shape and membrane sample that is suitable for practical use.

A Basic Study on a Rectangular Plane Space Sound Absorber Using Permeable Membranes

In this communication, the sound absorption characteristics of rectangular-shaped plane space sound absorbers without any backing structure using permeable membranes (PMs) are measured by reverberation room method. First, three types of PMs, in this study woven fabrics, are selected with different flow resistances and surface densities. They are prepared in the plane rectangular-shaped space absorbers of two different sizes. The measured results are discussed through comparison with the existing theoretical and measured results for absorbers of the other shapes or configurations. The present results and discussion demonstrate that the reverberation absorption coefficients of the proposed absorbers are low at low frequencies and converge to a moderately high value at high frequencies. Especially, ones with higher flow resistance than the air impedance converge to a value greater than 0.5, which is a theoretically estimated maximum absorption coefficient of infinite single-leaf PM. This is inferred to be attributed mainly to area effect. From these results the proposed absorbers can be used effectively despite of their very simple structure. Also it is found that the proposed absorber can offer higher sound absorption than permeable membrane absorbers of other shapes or configuration. Regarding the effect of the size, the absorbers of smaller size offer higher absorption coefficients regardless of material properties of the PMs used in the experiments.

Improved sound absorption performance of three-dimensional MPP space sound absorbers by filling with porous materials

Because microperforated panels (MPPs), which can be made from various materials, provide wide-band sound absorption, they are recognized as one of the next-generation absorption materials. Although MPPs are typically placed in front of rigid walls, MPP space sound absorbers without a backing structure, including three-dimensional cylindrical MPP space absorbers (CMSAs) and rectangular MPP space absorbers (RMSAs), are proposed to extend their design flexibility and easy-to-use properties. On the other hand, improving the absorption performance by filling the back cavity of typical MPP absorbers with porous materials has been shown theoretically, and three-dimensional MPP space absorbers should display similar improvements. Herein the effects of porous materials inserted into the cavities of CMSAs and RMSAs are experimentally investigated and a numerical prediction method using the two-dimensional boundary element method is proposed. Consequently, CMSAs and RMSAs with improved absorption performances are illustrated based on the experimental results, and the applicability of the proposed prediction method as a design tool is confirmed by comparing the experimental and numerical results.

Three-dimensional space sound absorbers using microperforated panels

A microperforated panel (MPP) is one of the most promising alternatives of the next-generation sound absorbing materials. It has a large potential for various use. However, its conventional use is to place it with a rigid-back wall and an air-cavity in-between. Therefore, its arrangements in a room are limited on to room boundaries, and in some cases, this may cause a problem in room design and its strength: for example, in Japan, it is not allowed by regulation to use it for a wall. Therefore, the authors have been looking at the possibility for using MPPs for space sound absorbers without any backing structure. This can allow MPPs for wider use: a three-dimensional shape MPP space absorbers can be easily produced if a suitable material is used. They can be placed easily in various places: they can be put on the floor or hang from the ceiling, etc. Besides, MPPs can be made of designable, lightweight materials, which can add designability to the absorbers. In this paper, the main results of our studies on three-dimensional MPP space absorbers (mainly cylindrical and rectangular three-dimensional MPP space absorbers) are introduced and summarized.

Numerical analysis of a three-dimensional permeable-membrane space sound absorber using boundary element method

Numerical analysis of a three-dimensional permeable-membrane space sound absorber using boundary element method

Numerical analyses of the sound absorption of cylindrical microperforated panel space absorbers with cores.

Microperforated panels (MPPs) are next-generation absorption materials because they can provide wideband sound absorption without fibrous materials and can be composed of diverse materials to meet global environmental demands. The fundamental absorbing mechanism is Helmholtz-resonance absorption due to perforations and an air cavity. MPPs are typically backed by rigid flat walls, but to reduce the restrictions on the MPP absorber properties, one of the authors has proposed MPP space sound absorbers without backing structures, including three-dimensional cylindrical microperforated panel space absorbers (CMSAs). Advantages of MPPs without backing structures are design flexibility and ease of use. Besides, the absorption characteristics of a CMSA with a core, which has a rigid cylindrical core inside the CMSA, have been experimentally tested, but a method to predict the absorption characteristics is necessary to design CMSAs with cores. Herein the two-dimensional combined Helmholtz integral formulation method is employed, and its prediction accuracy is evaluated by comparing the measured and predicted absorption characteristics of a CMSA with a core. Furthermore, a parametric study with regard to the core size is carried out to investigate the transition of the absorbing mechanism.

An experimental study on the absorption characteristics of a three-dimensional permeable membrane space sound absorber

In this study, we propose a rectangular and cylindrical three-dimensional space sound absorber using a permeable membrane and the absorption characteristics which are examined experimentally by reverberation room method. As a pilot study, a two-dimensional boundary element (2-D BEM) analysis is also conducted to predict the absorption characteristics of the absorbers. The experimental study revealed that the absorption coefficient is low at low frequencies and gradually increases with frequency. The absorption coefficient converges to 0.5 at the maximum which is similar to a single-leaf permeable membrane. The flow resistance and the surface density of the permeable membrane mainly affect the absorption characteristics at middle to high frequencies. At low frequencies, the heavy membrane contributes to the higher absorption performance. In the experiment specimens with high flow resistance produce higher absorptivity. Also, the cylindrical absorber shows slightly higher absorption coefficient than the rectangular absorber mainly at low frequencies. The 2-D BEM results show similar frequency characteristics as the measured values when the membrane's flow resistance and surface density are low, but the numerical values overestimate overall the absorptivity of the absorbers.

Effect of a porous absorbing layer on absorption characteristics of a double-leaf MPP space sound absorber

A micro-perforated panel (MPP) is usually placed in front of a rigid-back wall with an air-back cavity and forms a Helmholtz resonator with its holes and air-back cavity. However, the authors have so far proposed several kinds of MPP space sound absorber, which can absorb the sound energy without a rigid-back wall. A double-leaf MPP space absorber (DLMPP) is one of them, which is arranged with two MPPs in parallel without rigid-back wall. A DLMPP shows a peak absorption at the resonance frequency and additional absorption in a low frequency range. Therefore, a DLMPP can be used as a broadband space sound absorber in a practical situation. In this study, as an approach to improve its sound absorption performance, we propose a DLMPP with Porous which has a porous layer between two leaves of MPP, and its absorption characteristics are theoretically analyzed and discussed through the numerical examples. As a result, the absorption coefficient becomes 0.1…0.2 higher in all frequency ranges. The range of the resonance peak becomes broader. Thus, a porous layer can be said to improve the performance of a DLMPP.

Measurement of sound absorption coefficient of a rectangular plane space sound absorber comprising permeable membranes in a reverberation room

Measurement of sound absorption coefficient of a rectangular plane space sound absorber comprising permeable membranes in a reverberation room

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.

Numerical analyses of the sound absorption of three-dimensional MPP space sound absorbers

Because microperforated panels (MPPs) can provide wide-band sound absorption without fibrous and porous materials, they are recognized as next-generation absorption materials. The fundamental absorbing mechanism is Helmholtz-resonance absorption due to the perforations and air-back cavity. Consequently, MPPs are usually placed in front of rigid-back walls. However, one of the authors has proposed MPP space sound absorbers without backing structures. Among these space absorbers, cylindrical MPP space absorbers and rectangular MPP space absorbers are advantageous due to their design flexibility and easy-to-use properties. Although their performances have been investigated experimentally, it is necessary to predict their absorption characteristics to develop improved shapes and efficient designs. Herein their absorption characteristics are numerically predicted using the two-dimensional boundary element method, and the applicability of a numerical method as a design tool to sufficiently predict the performance of MPP space absorbers is discussed.

An experimental study on a cylindrical microperforated panel space sound absorber

A microperforated panel (MPP), which is widely known as one of the most promising alternatives of the next-generation sound absorbers, is typically used with a rigid-back wall with an air-cavity. However, a multiple-leaf MPP space absorber, which does not have any backing structure, double-leaf MPP space absorber (DLMPP) and triple-leaf MPP space absorber (TLMPP) is proposed. However, these are panel-like structure which are limited to where they can be used. In order to develop an MPP space absorber that can be used in more various situations, a trial production of a cylindrical MPP space sound absorber (CMSA) is made with an MPP shaped into a cylindrical. The sound absorption characteristics of a CMSA are measured in a reverberation chamber. As a result, although the absorption coefficient is not very high, a CMSA shows sound absorption characteristics similar to a DLMPP and TLMPP: a resonance peak by a Helmholtz resonator and an additional low frequency absorption by its acoustic permeability appear. The results suggest that a CMSA can be used as a space sound absorber in practical situations

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

Double-leaf microperforated panel space absorbers: A revised theory and detailed analysis

A double-leaf microperforated panel space absorber (DLMPP) is composed of two microperforated panels (MPPs) placed in parallel with an air-cavity in-between, without a back wall or any backing structure. This was proposed as a space sound absorber, which can be used for a sound absorbing screen or partition. A conventional MPP absorber with a rigid back wall is effective only around its resonance frequency, which is usually at middle frequencies, and not effective at low frequencies. However, a DLMPP can be effective also at low frequencies, because an additional sound absorption is produced by its acoustic flow resistance. In the authors’ previous work, theoretical analyses on the acoustic properties of a DLMPP were carried out using a simplified electro-acoustical equivalent circuit model. However, the equivalent circuit model includes an approximation, and more sophisticated theory is required for a better prediction and detailed discussion. In this paper, a revised theory for a DLMPP is presented: A Helmholtz integral formulation is employed to obtain a rigorous solution for more precise prediction of the absorptivity of a DLMPP. The result of the present revised theory is compared with that of the equivalent circuit model, and the difference between them is discussed. A parametric survey is made through numerical examples by the present revised theory to discuss its acoustic properties.