Good Sound Absorption Research Articles

Passive Suppression of Self-Excited Combustion Instabilities in Liquid Spray Flame Using Microperforated Plate

Abstract This paper presents an experimental investigation of using a microperforated plate (MPP) backed by an adjustable cavity to mitigate the combustion instabilities of liquid fuel swirl flame. The acoustic properties of MPPs with different porosities and aperture diameters were first tested in an impedance tube. At low bias flow rates, the sound reflection coefficients of MPPs with large holes commensurate well with the Luong model, and at high bias flow rates, the results of MPPs with small holes agree well with the predictions. The maximum sound absorption coefficient of each panel at the target frequency exceeded 95%. The perforated panels were then selected and integrated into a spray combustor individually. It was shown that the maximum reduction of pressure and heat release fluctuations inside the chamber was 14.91 dB and 13.40 dB, respectively. After noise elimination, the main frequencies of pressure and CH* signals were slightly shifted toward low frequencies. When the combustion conditions change, the MPPs operating near the optimal bias flow rates still have good sound absorption characteristics. After noise suppression, the synchronization between pressure and heat release signals was reduced, and the flame shapes were relatively stable. More generally, this study can promote the application of MPPs under bias flow in stabilizing the liquid spray combustion.

Effect of different factors on sound absorption property of porous concrete

As a functional pavement material with a large number of pores, porous concrete (PC) pavement exhibits a good sound absorption performance. Limited experimental studies focused on the effects of aggregate size, cement to aggregate ratio, and pavement thickness of porous concrete on its sound absorption in a wide range of sound frequencies. Besides, the effects of temperature and humidity on the sound absorption performance of porous concrete are still unclear. In this study, one hundred and thirty-five samples of porous concrete were prepared that consist of three aggregate gradations, three cement to aggregate (C/A) ratios and three thicknesses to investigate the sound absorption property of porous concrete considering the effects of temperature and humidity. These samples were tested at different temperatures (−10, 5, 20, 35 and 50 °C) and with different humidity (dry, inundated and saturated) using impedance tubes method with varied sound frequencies (200–2000 Hz). The results demonstrated that: under the same conditions, the sound absorption property of porous concrete decreases with the increase of aggregate size and cement to aggregate ratio, and increases with the increase of thickness. In addition, the temperature and presence of water have significant effects on the sound absorption property of porous concrete.

The Effect of Deviation Due to the Manufacturing Accuracy in the Parameters of an MPP on Its Acoustic Properties: Trial Production of MPPs of Different Hole Shapes Using 3D Printing

In this study, we discuss the effect of the manufacturing accuracy of a microperforated panel (MPP) produced by 3D printers on acoustic properties through measured and calculated results as a pilot study. The manufacturing costs of MPPs have long been one of their shortcomings; however, with recent developments in the manufacturing process, low-cost MPPs are now available. In a further attempt at reducing the cost, 3D printing techniques have recently been considered. Cases of trial production of MPPs manufactured by 3D printing have been reported. When introducing such new techniques, despite the conventional microdrill procedure, manufacturing accuracy can often become an issue. However, there are few studies reporting the effect of manufacturing accuracy on the acoustic properties in the case of 3D-printed MPPs. Considering this situation, in this pilot study, we attempted to produce MPPs with circular and rectangular perforations using a consumer 3D printer of the additive manufacturing type. The hole sizes of the specimens were measured, and the accuracy was evaluated. The normal incidence absorption coefficient and specific impedance were measured using an impedance tube. The measured results were compared with the theoretical values using Guo’s model. Through these basic studies, the MPPs produced by an additive manufacturing 3D printer demonstrated good sound absorption performance; however, due to the large deviations of parameters, the agreement with the theoretical values was not good, which suggests that it is difficult to predict the acoustic properties of MPPs made by a consumer-grade additive manufacturing 3D printer.

A Design Method for Labyrinth Sound Absorption Structure with Micro-perforated Plates

A kind of labyrinth sound absorption structure is constructed by embedding multi-layer micro-perforated plates into a pipeline, and a design method is proposed to optimize its parameters to ensure a good sound absorption performance. First, the effects of parameters of the labyrinth structure on the sound absorption performance are investigated. Second, a parameter optimization method is constructed based on the acoustic impedance transfer analysis and particle swarm optimization algorithm. Then, a simulation experiment is implemented by means of COMSOL to verify the optimization results. Finally, the labyrinth structures with straight pipeline, spiral pipeline and parallel pipeline are designed and their sound absorption performances are evaluated and compared. The research shows that, the effects of the perforation diameter, the plate thickness, and the perforation rate on the sound absorption performance are non-independent while the effect of the depth of cavity is independent; the weighting coefficient in the parameter optimization method could be adjusted to ensure a big absorption bandwidth in a low frequency range; in the frequency range of 30-4000 Hz, the labyrinth structure with straight pipeline and the labyrinth structure with spiral pipeline have the same sound absorption performance; for the labyrinth structure with parallel pipeline, the inner corner radius of pipeline has a great influence on the sound absorption performance, and the radius should be greater than 20mm.

Numerical and experimental study on metamaterials featuring acoustical and thermal properties

Metamaterials can be defined as materials which, for their peculiar composition or structure, exhibit characteristics that are not normally found in nature. “Multifunctional” metamaterials could be used to optimise different characteristics at the same time. In this paper the authors try to apply them for thermal and acoustic optimization of external building walls. Thermal optimization consists in obtaining a low transmittance, important in winter, and a low periodic thermal transmittance, important in summer. Acoustic optimization consists in obtaining high sound transmission loss, to respect the law prescriptions, and a good sound absorption coefficient, if possible. In this way should be possible enhance the comfort conditions in buildings and reduce the energy demand for winter heating and summer cooling. The proposed solution consists of several layers with different suitable characteristics: the sequence of the layers has been chosen with particular care. The thermal analysis has been performed by means of a self-developed code based on the ISO 13786 standard. The acoustic behaviour of the single layers has been determined following the procedure given by the ASTM E2611-09 standard using a four-microphone impedance tube and the transfer matrix method has been used for the complete assembly. This preliminary combined study showed encouraging results.

Acoustic simulation of cavities with porous materials using an adaptive model order reduction technique

Porous materials are often used in the context of passive noise control applications due to their low cost and good sound absorption properties. As the most commonly used predictive tool, the finite element (FE) method is often applied in the design phase to obtain detailed information on the performance of complex vibro-acoustic systems with porous damping treatments. In this case, however, its use inevitably leads to very large, complex-valued and frequency-dependent numerical models, which makes original full-order model evaluation intractable due to time and memory limitations. In this paper, an adaptive model order reduction strategy is presented to reduce the number of degrees of freedom involved in the associated problems such that the required computational cost can be largely alleviated while a desired high accuracy can be achieved in a controllable way. This technique consists of making use of Taylor expansion to the multiple frequency-dependent scalar functions coming from the complex material behavior, and then performing the structure-preserving second-order Arnoldi algorithm based on a robust error indicator to solve the underlying FE model in the frequency domain. A further improvement in terms of the approximation accuracy of the constructed compact reduced-order model is also proposed to incorporate all available moment-matching information. Two widely used model types for porous materials are investigated, i.e. the equivalent fluid description and the Biot theory. Mono-physical poroelastic-poroelastic coupling and multi-physical acoustic-porous coupling are considered in order to demonstrate the simplicity, versatility and efficiency of the approach.

On-demand optimize design of sound-absorbing porous material based on multi-population genetic algorithm

Abstract Porous material (PM) shows good sound absorption performance, however, the sound absorbing property of PM with different parameters are greatly different. In order to match the most suitable absorbing materials with the most satisfactory sound-absorbing performance according to the noise spectrum in different practical applications, multi-population genetic algorithm is used in this paper to optimize the parameters of porous sound absorbing structures that are commonly used according to the actual demand of noise reduction and experimental verification. The results shows that the optimization results of multi-population genetic algorithm are obviously better than the standard genetic algorithm in terms of sound absorption performance and sound absorption bandwidth. The average acoustic absorption coefficient of PM can reach above 0.6 in the range of medium frequency, and over 0.8 in the range of high frequency through optimization design. At a mid-to-high frequency environment, the PM has a better sound absorption effect and a wider frequency band than that of micro-perforated plate. However, it has a poor sound absorption effect at low frequency. So it is necessary to select suitable sound absorption material according to the actual noise spectrum.

Diffuse Sound Absorptive Properties of Parallel-Arranged Perforated Plates with Extended Tubes and Porous Materials.

The diffuse sound absorption was investigated theoretically and experimentally for a periodically arranged sound absorber composed of perforated plates with extended tubes (PPETs) and porous materials. The calculation formulae related to the boundary condition are derived for the periodic absorbers, and then the equations are solved numerically. The influences of the incidence and azimuthal angle, and the period of absorber arrangement are investigated on the sound absorption. The sound-absorption coefficients are tested in a standard reverberation room for a periodic absorber composed of units of three parallel-arranged PPETs and porous material. The measured 1/3-octave band sound-absorption coefficients agree well with the theoretical prediction. Both theoretical and measured results suggest that the periodic PPET absorbers have good sound-absorption performance in the low- to mid-frequency range in diffuse field.

Innovative Use of Sheep Wool for Obtaining Materials with Improved Sound-Absorbing Properties

In recent years, natural materials are becoming a valid alternative to traditional sound absorbers due to reduced production costs and environmental protection. This study explores alternative usage of sheep wool as a construction material with improved sound absorbing properties beyond its traditional application as a sound absorber in textile industry or using of waste wool in the textile industry as a raw material. The aim of this study was to obtain materials with improved sound-absorbing properties using sheep wool as a raw material. Seven materials were obtained by hot pressing (60 ÷ 80 °C and 0.05 ÷ 6 MPa) of wool fibers and one by cold pressing. Results showed that by simply hot pressing the wool, a different product was obtained, which could be processed and easily manipulated. The obtained materials had very good sound absorption properties, with acoustic absorption coefficient values of over 0.7 for the frequency range of 800 ÷ 3150 Hz. The results prove that sheep wool has a comparable sound absorption performance to mineral wool or recycled polyurethane foam.

Sound absorption, thermal, and flame retardant properties of nonwoven wall cloth with waste fibers

In order to solve the recycling problem of waste fibers, the nonwoven wall cloth was prepared with waste wool fibers and low-melting-point polyamide fibers as raw materials by combing into a net and hot-pressing method. The effect of fiber length, hot pressing temperature, mass fraction of the waste wool fibers, volume density, thickness of materials, and thickness of the rear air layer on the sound absorption properties were studied by single factor experiments. Under the optimized technological conditions, the sound absorption coefficient was above 0.91 and the noise reduction coefficient was 0.56. Then, the sound absorption mechanism was analyzed. In order to meet the fire resistance requirements of materials in the construction industry, by the orthogonal experiments, range analysis, and variance analysis, the optimal process conditions were as follows: potassium fluotitanate concentration of 8%, treatment time of 40 min, and treatment temperature of 80°C. The limit oxygen index of the nonwoven wall cloth was 32.5%. The nonwoven wall cloth had good sound absorption and flame retardant properties.

The Physical, Mechanical, and Sound Absorption Properties of Sandwich Particleboard (SPb)

While the utilization of wood as a raw material in related industries has been increasing with the population increasing, the availability of wood from natural forests has continued to decline. An alternative to this situation is the manufacture of particleboard from non-wood lignocellulose materials through the modification of sandwich particleboard (SPb) using bamboo strands as reinforcement. In this study, strandsof belangke bamboo (Gigantochloa pruriens W) and tali bamboo (Gigantochloa apus) were utilized. The non-wood particles included sugar palm fibers, cornstalk, and sugarcane bagasse. The board was made in a three-layer composition of the face, back, and core in a ratio of 1: 2: 1. The binder used was 8% isocyanate resin. The sheet was pressed at a temperature of 160°C for 5 min under a pressure of 3.0 N/mm2. Testing included physical and mechanical properties based on the JIS A 5908 (2003) standard, while acoustic testing was based on ISO 11654 (1997) standards. The results showed that using bamboo strands as reinforcement has an effect on the mechanical and physical properties of SPb. Almost all the types of boards met the JIS A 5908 (2003) standards, with the exception of thickness swelling (TS) and internal bond (IB) parameters. Based on the thickness swelling parameter, the C-type board exhibited the best properties. Overall, the B-type board thatused a belangke bamboo strand for the surface and sugarcane bagasse as the core underwent the best treatment. Based on the acoustical parameter, boards using a tali bamboo strand for the surface and sugar palm fiber as the core (E-type board) exhibited good sound absorption properties.

Preparation of foamed aluminum and its application in China

As a new structural material combined with functional characteristics, aluminum foam possesses low density, high specific surface area and stiffness, good sound and energy absorption, as well as excellent electromagnetic shielding. Among the preparation ways which can be used to fabricate aluminum foam, the methods, such as direct foaming in aluminum melt, melt foaming by gas injection, powder metallurgy route and casting around space holder materials, may be the main ones. The R & D of the methods above in China is discussed in this paper. Aluminum foams have been exploited in road noise barrier, buildings, rail transit vehicles, aerospace and bridge protection in China nowadays. The applications of aluminum foams obtained by some methods are also emphatically described. It is speculated that the application fields and amount of the aluminum foams may be increased in the future along with the further development of Chinese economy.

Flexible micro-perforated panels prepared by CNC machining

With the advantages of light weight, thin thickness and environment friendly, the micro-perforated panel (MPP) has been widely studied for noise reduction. Maa’s model pointed out that the MPP could obtain higher sound absorption over broader frequency band when the perforations were reduced to less than 100 μm. However, it is challenging to manufacture MPPs with the aperture of approximate 100 μm, thus its potential application has been restricted. In this study, we used a computer numerical control (CNC) milling machine to process MPP. Four different kinds of raw materials including paperboard, polyethylene terephthalate (PET), polyvinyl chloride (PVC), and polycarbonate (PC) were taken to prepare micro-perforated panels (MPPs). It has been indicated that MPPs with good sound absorption properties were successfully prepared by this facile method.

Experimental study on sound absorbing property of spatial absorber of non-woven fabric with micro-perforated plate-like structure

Microperforated panel (MPP) absorbers have been widely used in noise reduction and are regarded as a promising alternative to the traditional porous materials. However, the flat panel-like shape restricts their practical use in actual rooms or buildings. To overcome these limitations, three-dimensional MPP spatial sound absorbers have been proposed. MPP are mostly metal materials with high cost. It is relatively easy to make cylinders or cubes, and difficult to make other complex structures. In view of this, a kind of non-woven material which can replace micro-perforated board is proposed in this paper. This kind of non-woven material has the characteristics of low cost, flexibility, convenient moulding and good sound absorption performance. The impedance tube experiments has been employed to study the normal incidence sound absorption coefficient for the non-woven fabric materials. The experimental results show that the sound absorption properties of non-woven fabrics are similar to those of ultra-micro MPP. Three kinds of spatial sound absorbers have been made by non-woven materials. They are the hollow cylindrical, fan-shaped, and honeycomb-like spatial sound absorbers, respectively. The measurement of reverberation chamber results show that the sound absorption capacity of the honeycomb-like spatial sound absorber is better than the hollow cylindrical and fan-shaped spatial sound absorbers. Adding non-woven cylindrical boundary layer can further improve the sound absorption performance of the fan-shaped and honeycomb-like space absorber.

Fabrication of novel formulations from rigid polyurethane foams and mortar for potential applications in building industry

Rigid polyurethane (PU) foams are widely used in modern life owing to excellent strength and weight carrying capacity. Most of the rigid PU foams in the market are based on polypropylene oxide (PPO) and methylene diphenyl diisocyanate. Amine catalysts, especially tertiary amines, are used to balance both the gelling and gas-foaming reactions, responsible for foam formation. The objective of present work is to prepare rigid PU foams from PPO based polyol and 4,4′- methylene diphenyl diisocyanate (MDI). The morphological and mechanical properties of polyurethane foam using tertiary amine and water blowing agent have been investigated. Moreover, acoustic and thermal insulation of polyurethane foam ordinary Portland cement mortar formulations were also examined. The results indicated that polyurethane ordinary Portland cement mortar formulations have good sound absorption and thermal insulation characteristics compared to blank formulations.

A novel sound absorbing material comprising discarded luffa scraps and polyester fibers

Abstract For promoting the recycling of industrially discarded luffa resources and preventing environmental pollution caused by the incineration of luffa waste, abundant luffa scraps and environmentally friendly polyester fibers were used as raw materials to produce luffa fiber sound absorbing composites by the clean hot-pressing technology. Results revealed that the polyester fiber surface becomes rougher, with a large number of porous structures, affording a three-dimensional network after hot-pressing. Within the range of the test design, the sound absorption coefficient of the samples increased with increasing density, thickness, and distance of the back air gap. With the increase in the thickness from 2 cm to 6 cm, the average sound absorption coefficient of the material increased from 0.442 to 0.684, and the maximum sound absorption coefficient increased from 0.907 (4000 Hz) to 0.991 (1000 Hz). At back air gap distances of 0 cm, 1 cm, and 2 cm, their average sound absorption coefficients were 0.602, 0.606, and 0.645, respectively. At a density of 0.09 g/cm3, a thickness of 4 cm, and a back air gap distance of 2 cm, the average sound absorption coefficient of the luffa fiber composite reached 0.645, revealing a high-efficiency sound absorbing material. In addition to exhibiting a good sound absorption performance, the luffa fiber composite exhibited a soft surface and good buffer performance. Moreover, compared to other plant fiber composites, the luffa fiber composite exhibited better performance for hygroscopic and moisture dissipation.

Application of Inorganic High-strength Sound Absorbing Board in the Assembly Module of Residential Integrated Ceiling

Inorganic high-strength sound absorption board is a kind of inorganic composite material based on natural gypsum, and it is often used in interior decoration of residential buildings with good sound absorption properties. Based on the development trend of prefabricated buildings and full decoration of residential buildings, the green and environmental friendly inorganic high-strength sound absorption board is selected as the decoration materials for the practice of residential integrated ceiling module engineering project, and the design examples and process technologies of the residential integrated ceiling assembly modules are introduced in combination with the architectural acoustic principle, which provides reference value for the development of assembled interior installation technology of buildings.

Tailoring Acoustic Performances of Resin Reinforced Biomass Fiber-Based Panel with Single and Multiple Tailed Cavity Inclusions for Interior Work

The aim of this research is to observe the acoustic performance of absorber-based biomass fiber-reinforced polyester resins that were experimentally associated with the design of tailed cavity resonator inclusion, i.e., the cavities are partly in the form of a narrow slit. The model of electro-acoustic resonators and several treatments were developed and became the bases for understanding the changes of acoustic reactance in the new structure. Variations in the inclusion cavity and the addition of a narrow slit were tested experimentally using an impedance tube technique based on ASTM E1050-98 and ASTM E2611-09. The improvements of acoustic performance were conducted by single and multiple cavity tailed inclusions with the addition of a Dacron fibrous layer and back cavity. The experimental results showed that a sample of 15 mm single tailed cavity kenaf fiber had higher sound absorption and wider broadband frequencies than did the hemp fiber, with a peak on 0.31–0.32 between 1.00–2.00 kHz. Meanwhile on multiple tailed cavities, the 30 mm hemp fiber had higher and wider broadband frequencies than did the kenaf, with peaks on 0.45–0.63 at frequencies between 1.75–2.10 kHz. It can be concluded that the tailed cavity inclusions could improve performance. Compared to the coco-husk with resonators in previous studies, the tailed cavity was a little bit lower, but the tailed cavities hemps and kenafs samples showed good sound absorption performance with lower band frequencies capabilities.

A flexible silica aerogel with good thermal and acoustic insulation prepared via water solvent system

In this paper, transparent flexible hydrophobic silica aerogels were prepared by replacing the traditional alcohol solvent with water, using methyltriethoxysilane (MTES) and cetyltrimethylammonium bromide (CTAB), via acid-base two steps method and CO2 supercritical drying. The role of surfactant CTAB in the gel–sol process was revealed, and the effect of CTAB concentration on the gel structure was analyzed. With the concentration increasing, the skeleton structure of the gel gradually changed from coarse graininess to continuous fiber. The obtained aerogels showed good elastic properties. With the increasing of density, the elastic modulus of aerogels gradually increased, so that the length could be restored to 63% of the original length after 50% compression strain. Aerogels also had low thermal conductivity and good thermal stability. The thermal conductivity at room temperature was only 0.0215 W/(m·K) and the initial decomposition temperature was up to 511 °C. For the aerogel with thickness of 11.8 mm and density of 60 mg/cm3, it showed good sound absorption and sound insulation properties. When the sound frequency was 2000 Hz, the sound absorption coefficient was 0.91, and the sound transmission loss between 500 and 1600 Hz was 13–21 dB. This work provides a facile approach to fabricate lightweight and flexible silica aerogels for thermal and acoustic insulation applications.

The Cushion Performance of Mycelium-Cornstraw Biofoams

Biofoams are considered to be one of the best alternatives to polymer foam. In many biofoams, mycelium-based biofoams are favored in the recent years for its zero pollution and renewability during the forming and after treatment process. Mycelium-wood biofoams, mycelium-cottonseed shell biofoams have been proved to have good mechanical or sound absorption properties. While, whether corn straw, as the by-product of the largest yield of agricultural products, is suitable to prepare mycelium-based biofoam has not been studied yet. Here we used Pleurotus ostreatus mycelium bonding corn straw to prepare mycelium-cornstraw biofoams, and mechanical properties as well as bonding mechanism of the mycelium-cornstraw biofoams were studied. It was discovered that inoculum quantity was an important factor on the performance of mycelium-cornstraw biofoams, and inoculum quantity of 1.8% was considered as the optimal inoculum quantity. At this inoculum quantity, when relative deformation was 10%, the compressive strength of mycelium-cornstraw biofoam was about twice that of mycelium-broadleaf sawdust biofoams reported, but the time spent on material preparation is only about their 1/3.