No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Optimization Design of Serial-Parallel Coupled Micro-Perforated Panel Absorbers by Genetic Algorithm
... Since the acoustic performance of parallel-connected MPPs depends on 4N parameters, it is difficult to know a priori the combination of these parameters providing the maximum absorption within a prescribed frequency band. Authors have used several optimization algorithms such as simulated annealing [11], genetic algorithm [12], and Particle Swarm Optimization [13]. After achieving some optimized parameters for specific panels, it can be manufactured and therefore can be used as a wall/ceiling panel in architectural applications. ...
This study aims to synthesize the theoretical background required for the design of wideband acoustic absorbers. For acoustic materials to have wideband absorption, especially in the low-frequency range, their design should include a combination of resonant mechanisms such as membranes and Micro-Perforated Panels (MPPs). The current work uses an electro-acoustical circuit model to understand the absorption mechanisms of such complex systems. Theories related to the resonance mechanism of MPPs have been widely discussed. Five variables affecting the resonance of one MPP structure are its holes' diameter, the distance between holes (perforation ratio), the thickness and area density of the panel material, and the cavity behind the structure backed by a rigid/absorptive wall. By tuning these variables, it is possible to achieve wideband absorption for desired frequencies. Moreover, parallel combinations of different MPPs showed to have a better performance at absorbing a broader frequency range.
The acoustic properties of a compound micro-perforated panel (MPP) absorber array are investigated. The absorber array consists of three parallel-arranged MPP absorbers with different cavity depths. A finite element procedure is used to simulate its acoustic behaviors under normal incidence. Experimental studies are carried out to verify the numerical simulations. Due to different reactance matching conditions in the absorber array, strong local resonance occurs and the corresponding local resonance absorption dominates. Compared with single MPP absorber, the absorber array requires lower acoustic resistance for good absorption performance, and the resonance frequencies shift due to inter-resonator interactions. The different acoustic resistance requirement is explained by considering the reduced effective perforation rate of the MPP in the absorber array. The performance of the absorber array varies with the sizes and spatial arrangement of the component absorbers. When the distance between component absorbers is larger than a quarter-wavelength, the above-mentioned parallel absorption mechanism diminishes. In the experimental study, the normal incidence absorption coefficients of a prototype MPP absorber array are tested. The measured results compare well with the numerical predictions. The experimental study also shows that although other absorption mechanisms may exist, dissipation by the MPP is dominant in the MPP absorber array.
Micro-perforated panel (MPP) absorber has been widely used in noise control and is regarded as a promising alternative to the traditional porous materials. However, the absorption bandwidth of single MPP absorbers is always insufficient to compete with the porous materials. In this paper, aiming at obtaining high absorption over broad frequency band, a compound MPP absorber array adopting the series-parallel coupling manner is proposed and investigated. Firstly, a theoretical model for the normal absorption coefficient of the series-parallel coupled MPP absorber is established based on the electrical circuit analysis. And then measurements of the normal incidence absorption coefficients are carried out to verify the theoretical predictions. The experimental data are in agreement with the theoretical calculation and prove that the composite structure has the characteristics of broadening the absorption bandwidth through a combination of serial and parallel coupling, which may provide a new technique to improve the absorption performance of such type of MPP absorbers.
Based on MAA Dah-You's general theory of the microperforated absorber, three layers microperforated structure absorption coefficient was calculated. By genetic algorithm parameters of the structure are optimized and its characteristic of absorption is analyzed. Optimal design of three layers microperforated panel can get more satisfactory absorption curve than double microperforated panel during the usual noise frequency area. Its absorption coefficient is almost equal to convention absorb material. A experiment is carried out to prove this optimal design.
General theories of the acoustic impedances of an orifice and of a perforated panel are reviewed. The perforated panel with the size of the perforations reduced sufficiently will make a good absorbing element alone, with proper acoustic resistance and low mass reactance. It is shown that the frequency band of sound absorption of a perforated-panel construction depends essentially on the diameter of the perforations, and good absorption is obtained only with microperforated panels with submillimeter holes. A double-resonator type absorber extends the absorption to lower frequencies, the extent of which depends mainly on the combined cavity. The absorption also extends to higher frequencies when the absorbers are used in a random field, and wideband sound absorption is feasible without the use of porous materials. Quantitative analyses are presented, and straightforward design procedures outlined. Numerical examples are given. Possibilities and limitations of microperforated-panel construction are discussed.
Micro-perforated panels have been used for duct silencing for several years and are gaining popularity. This paper presents equations for predicting the sound attenuation of micro-perforated panel silencers. It also presents guidelines for silencer geometric parameter selection to improve silencer performance. The guide-lines are taken from both silencer tests and theoretical analyses. (C) 1997 Institute of Noise Control Engineering.
The calculation of resonance and anti-resonance frequencies of a double layer microperforated sound absorption structure is studied, and simplified analytical formulae which will be very useful for the design and analysis of wide bandwidth double layer microperforated sound absorption structures are derived. The results obtained provide an effective method for the design of wide bandwidth microperforated panel silencers.
Many applications have been found for the microperforated panel (MPP) absorber, on which the perforations are reduced to submillimeter size so that they themselves will provide enough acoustic resistance and also sufficiently low acoustic mass reactance necessary for a wide-band sound absorber. The most important parameter of the MPP is found to be the perforate constant k which is proportional to the ratio of the perforation radius to the viscous boundary layer thickness inside the holes. This, together with the relative (to the characteristic acoustic impedance in air) acoustic resistance r and the frequency f(0) of maximum absorption of the MPP absorber, decides the entire structure of the MPP absorber and its frequency characteristics. In other words, the MPP absorber may be designed according to the required absorbing characteristics in terms of the parameters k, r, and f(0) Formulas and curves are presented toward this end. It is shown that the MPP absorber has tremendous potential for wide-band absorption up to 3 or 4 octaves and for low-frequency absorption with a cavity of depth small compared to the wavelength. Techniques of making minute holes (of 0.1-0.3 mm, say) have to be developed, though. (C) 1998 Acoustical Society of America. [S0001-4966(98)05710-5]
As investigated by the Occupational Safety and Health Act (OSHA) in 1970, noise is highly responsible for the psychological and physiological ills to workers. Therefore, the noise control for an enclosed system with high echo effect becomes essential. Besides, the thickness of adopted sound absorber is occasionally constrained for maintenance, the interest in minimizing the noise under space constraint is then arising. In this paper, the shape optimization of double-layer absorber together with genetic algorithm (GA) is presented. Before optimization, one example is tested and compared with the experimental data for accuracy check of mathematical model. Thereafter, a simple optimal program in dealing with pure tone noise of 350 Hz has been pre-run to verify the correctness of genetic algorithm before the design in full band noise being performed. Results show that both the accuracy of mathematical model and the correctness of GA method are acceptable. Consequently, this study may provide a novel scheme with GA in solving the shape optimization of sound absorber on the constrained sound absorption system. Copyright © 2004 John Wiley & Sons, Ltd.
In the acoustic consulting, testing, design and engineering work of the Fraunhofer-Institute of Building Physics (IBP) the low-frequency end of the noise spectra and the room acoustic conditioning has gained tremendous importance over the years. For solving the long-ranging noise pollution from e.g. exhaust stacks and chimneys, a series of low-frequency sound attenuators with minimum flow resistance were developed. Its first representative was a novel membrane absorber [10] [Ackermann U, et al., Sound absorbers of a novel membrane construction. Applied Acoustics 1998;25:197–215]. Thanks to its slenderness and ruggedness it could also be employed for noise control and reverberation adjustment purposes in relatively narrow enclosures and harsh environments and [Vér IL. Enclosures and wrappings. In: Harris CM, editor. Handbook of acoustical measurements and noise control. New York: McGraw-Hill, 1991; Fuchs HV, Hunecke J. The room plays its part at low frequencies. Das Musikinstrument 1993;42:40–6 (in German). Meanwhile a new type of panel absorber has been optimized for both kinds of application. Its absorption efficiency at frequencies far below 100 Hz could be demonstrated and quantified by a special measuring procedure based on the reverberation of a small rectangular room at its eigenfrequencies [3] (Zha X, et al. Measurements of an effective absorption coefficient below 100 Hz. Acoustics Bulletin 1999;24:5–10). With the aid of this novel tool it is now possible to qualify reverberation rooms and anechoic chambers for frequencies down to 63 and 31 Hz, respectively [9] (Fuchs HV, et al. Qualifying freefield and reverberation rooms for frequencies below 100 Hz. Applied Acoustics 2000;59:303–22). In a companion paper in this same journal [4] [Fuchs HV, et al.: Creating low-noise environments in communication rooms. Applied Acoustics (in print)] appropriate experience is reported in creating low-noise environments in multi-purpose rooms like offices, restaurants, foyers and seminars. A number of representative case studies [5] (Drotleff H, et al. : Attractive acoustic design of multi-purpose halls. 1. Chinese–German Platform Innovative Acoustics 2000, (October, 21–25. 2000)) show ample evidence that the low-frequency performance of the rooms has a strong influence on both the amplification of intruding external noise and the development of internally generated noise emanating from communication processes provoked by the users themselves. At work places where producing sound (by voices or/and instruments) is the main or only purpose for their existence, the acoustic qualification of the room at low frequencies turns out to be of the utmost importance, especially when musicians are forced to work in extremely narrow spaces like orchestra pits and rehearsal halls for many hours a day and often under extreme physical and mental pressure. The measures taken and described herein have proven to mitigate if not remove some of the acoustic burden put on musicians employed in states theatres.
As a research, development and consulting institute the IBP has frequently been confronted with external (intruding from outside) and internal (self-generated inside) noise in communication areas of one kind or another. As a fundamental discovery it has become obvious that the frequency range far below that covered by building and room acoustic standards is of the utmost importance for the sound generation and speech intelligibility process. A powerful new tool for tackling low-frequency problems was invented in the form of slender compound panel absorbers (CPA) to be mounted on (or integrated in) walls or ceilings as an efficient means to damp the dominant eigenfrequencies of the room itself. Since literature on the rather obscure phenomena observable below 125 or 100 Hz in real-life conversations was found to be very scarce, a large variety of acoustically unsatisfactory enclosures was investigated beyond the standard frequency limits and subsequently cured with some really convincing improvements experienced in acoustic comfort and sound quality. This paper was written as an advise and warning for acoustic consultants (not scientists) dealing with the often torturing acoustics in preferably hard-walled office, conference, foyer, restaurant or class rooms (not studios). The still growing problem of low-frequency room responses does not allow waiting for more academic studies and recognized extensions and adjustments of the valid measuring standards and regulations. Responsible acousticians should at least be aware that conventional single-number ratings for sound power, transmission and absorption are not of much help when dealing with this omnipresent problem which seems to have passed unnoticed even by experts in this field.
The paper examines the feasibility of using transparent micro-perforated absorbers (MPA) in a window system to allow noise attenuation whilst at the same time maintaining high levels of comfort ventilation and daylighting. The underlying theory for micro-perforated panels and membranes and the application in silencers is presented. Experiments have been performed between a semi-anechoic and a reverberant chamber using a standard window mock-up, and the effectiveness of MPA has been demonstrated. With a constant air backing, MPA are more effective with a wider ventilation path. With an air flow of up to 2 m/s the performance of the MPA remains unchanged. Current results are based on readily available materials and relatively simple configurations, but the theoretical analysis suggests possibilities for increasing the noise reduction and widening the frequency range by using more strategically designed materials and configurations.
