Acoustic Panels Research Articles

In Memoriam: Dr. Clive L. Dym (1942–2016)

In Memoriam: Dr. Clive L. Dym (1942–2016)

EVALUATION OF THE REVERBERATION TIME IMPROVEMENT IN A SPEAKING HALL

To improve a room's acoustic parameters there have been studied several variants of acoustic materials and devices that can be placed on the ceiling of the hall. The main objective of the study was the reverberation time measurement and calculation. By using the acoustic panel made from polystyrene, covered with jute on the both sides, has ensured the largest reverberation time decrease. Thus, we can say that the analyzed room can be used for speech activity (courses, conferences etc.)

MANUFACTURE OF ACOUSTICAL ONE SIDE-WAFFLE PANEL MADE OF NATURAL RESOURCES WITH HYDRAULIC HOT PRESS MACHINE

Waste generated from natural resources should be recycled as more useful materials. This research has produced acoustical waffle panel material which is useful as an absorber on the noisy housing. Acoustical waffle panels was made by Hydraulic Hot Press machine. The purpose of this discussion is to describe the machine design process and compare waffle panels made of coconut fiber and wood sawdust in the best acoustic performances. The result is that the hydraulic hot press machine has the structural strength and stability on the load of 2,500 N and 5,000 N. The hot press machine is safe for both the transverse tensile stress and longitudinal tensile stress which are smaller than the allowable stress of steel material of 40 at 1,100 kg/cm2. It also has the highest Sound Transmission Loss (STL) with the value of 40. 059 dB.

Investigation studies involving sound absorbing parameters of roadside screen panels subjected to aging in simulated conditions

Abstract The paper presents the results of investigation studies involving the impact of atmospheric factors on sound-absorbing parameters of roadside acoustic screen panels. The research studies comprised the aging test consisting of 1000 cycles in simulated conditions, sound absorption measurements and surface morphology tests, using the SEM scanning method. The simulation of aging consisted of 100 or 150 cycles at a time. Then, the panels were investigated in the reverberation chamber to define their sound-absorbing properties. The process was repeated until 1000 cycles were completed. Basing on the carried out tests, a statistical linear model was worked out which was used to estimate the value of a single number sound absorption coefficient after successive aging cycles. The optimality of the model was demonstrated by means of a statistical test confirming normal distribution of random residuals. For the research studies, we employed an innovative structural design of panels for which aging characteristics were obtained. Basing on the obtained results and on the statistical analysis, the prospects to maintain acoustic properties of the panels during their service life was estimated.

The noise control of minicar body in white based on acoustic panel participation method

It is very important to predict the acoustic radiation of vehicle body for the control of interior noise. Firstly, the kinetic equations of coupled acoustic-structural finite element method are explained and the numerical analytical methods of noise transfer function and acoustic panel participation are further obtained. Then the coupled acoustic-structural finite element model of body in white and passenger compartment cavity of a minicar is established and verified by modal test. The passive side of engine mounting points are chosen as the excitation points, and driver’s right ear is the output point of sound pressure response. The noise transfer function is calculated and the critical frequency of vehicle interior noise is obtained. The acoustic panel participation analysis of vehicle roof and floor are conducted, and the key acoustic panels are identified. In order to reduce the noise of critical frequency, the measures, pasting damping material and welding beam, are adopted. The results indicate that, compared with the results of structure improvement of modal method, the vehicle interior noise is controlled more effectively by using the acoustic panel participation analytical method.

Effect of Granule Sizes on Acoustic Properties of Protein-Based Silica Aerogel Composites via Novel Inferential Transmission Loss Method

The acoustic properties of the silica aerogel (SA) granules of various sizes from 0.50 to 3.35 mm, distributed into six groups of nominal sizes and measured via a two-microphone impedance tube, are presented. The absorption coefficients of the SA granules were evaluated at ultra- to super-low frequency range from 50–1600 Hz. It was observed that nominal SA granules with sizes of 1.2 mm (AG2) and 1.7 mm (AG3) displayed the best absorption coefficients. When tested with granules filled at 5 cm depth, AG2 and AG3 absorption coefficients peaked at 980 Hz with values of 0.86 and 0.81, respectively. A novel approach to measure transmission loss (TL) by using “inferential” principle is presented. This novel method, named “Inferential Transmission Loss Method” (InTLM), revealed that the average TL, for both AG2 and AG3 SA granules was 14.83 dB and 15.35 dB, respectively. Gelatin silica aerogels doped with sodium dodecyl sulfate (GSA–SDS) composites comprising of 1.2 mm (GSA–AG2) and 1.7 mm (GSA–AG3) granules of various configurations were fabricated and evaluated for absorption coefficients and TL with known traditional acoustic panels. The results showed that GSA–AG3 had a better absorption coefficient over other configurations for the same corresponding thickness reaching the peak of 0.6 from 1300 to 1450 Hz with between 10.7 and 20.3 decibels. The four-layered GSA–AG2 and GSA–AG3 composites showed exceptionally high absorption from 500 to 800 Hz suitable for narrow band applications. Lastly, the “InTLM” was matched with the sound meter measurements, with high accuracy between 0.3 and 3.2 dB for low-frequency testing (50–1600 Hz).

Desempenho acústico de painéis de gesso incorporados com fibras de celulose

Currently, with the rationalization of consumption of raw materials due to energy constraints and possible damage to the environment , it has tried to maximize their employability . The forestry - wood sector is largely responsible for the generation of waste , which must be allocated appropriately to not lead to environmental damage. Thus, this study aimed to evaluate the acoustical panels made of plaster embedded with cellulose fibers from a pulp and paper company of the Paulista West . The evaluation was made based on the sound absorption material, resulting in sound absorption coefficients at around X, according to values found in literature.

Traditional and Innovative Materials for Energy Efficiency in Buildings

This chapter shows the most recent and innovative contributions and research trends arounbd the wide issue of energy efficiency in buildings by means of passive techniques, such as new effective materials for building envelope optimization. In particular, cool materials will be dealt with by considering their capability to keep a surface cooler than other solutions when exposed to solar radiation. Then multifunctional materials such as thermal and acoustic insulation panels will be analyzed. Finbally, natural and biobased solutions for energy saving will be investigated. Each one of these topics will be studied by elaborating a first general assessment of each technique and then by analyzing the most recent contributions and research trends in order to provide a wide perspective of the question that is going to be addressed in this chapter.

Characterization of geopolymer fly-ash based foams obtained with the addition of Al powder or H2O2 as foaming agents

Recent innovations in geopolymer technology have led to the development of various different types of geopolymeric products, including highly porous geopolymer-based foams, which are formed by the addition of foaming agents to a geopolymer fly-ash based matrix. These agents decompose, or react with the liquid matrix or oxygen in the matrix, resulting in the release of gases which form pores prior to the hardening of the gel. The hardened structure has good mechanical and thermal properties, and can therefore be used for applications in acoustic panels and in lightweight pre-fabricated components for thermal insulation purposes.This study presents the results of the pore-forming process in the case when two different foaming agents, i.e. aluminium powder amounting to 0.07, 0.13 and 0.20 mass. % and H2O2 amounting to 0.5, 1.0, 1.5 and 2.0 mass. %, were added to a fly-ash geopolymer matrix. The physical, mechanical, and microstructural properties of the thus obtained foams, and the effects of the type and amount of the added foaming agent, are presented and discussed. Highly porous structures were obtained in the case of both of the investigated foaming agents, with overall porosities up to 59% when aluminium powder was added, and of up 48% when H2O2 was added. In the latter case, when 2% of the H2O2 foaming agent was added, finer pores (with diameters up to 500μm) occurred in the structure, whereas somewhat larger pores (some had diameters greater than 1mm) occurred when the same amount of aluminium powder was added. The mechanical properties of the investigated foams depended on their porosity. In the case of highly porous structures a compressive strength of 3.3MPa was nevertheless achieved for the samples containing 0.2% of aluminium powder, and 3.7MPa for those containing 2.0% of H2O2.

ジェットエンジンにおける消音パネルを設置したファンダクト流の数値解析

Noise suppression is of importance for jet engines. Acoustic panels installed in the fan duct can reduce the noise emission while it induces the pressure loss. In order to achieve the suppression of the noise emission and the low duct loss simultaneously, we have designed new acoustic panel and conducted implicit large eddy simulations of the duct flow with the panel in this study. Since the Mach numbers in the duct and the hole of the cavity are extremely different, we have employed an all speed Roe scheme for compressible flow solvers. The turbulence is induced by a roughness block. We have found that the turbulent boundary layer becomes thinner just downstream of the hole in the duct since a part of the turbulence goes into the cavity.

ЭКСПЕРИМЕНТАЛЬНОЕ ИССЛЕДОВАНИЕ ВЛИЯНИЯ ДЕФЕКТОВ НА ПРОЧНОСТЬ КОМПОЗИТНЫХ ПАНЕЛЕЙ МЕТОДАМИ КОРРЕЛЯЦИИ ЦИФРОВЫХ ИЗОБРАЖЕНИЙ И ИНФРАКРАСНОЙ ТЕРМОГРАФИИ

The article is devoted to the experimental investigation of the defects influence on the residual strength of composites structure, as well as the possibility of using local repair operations. The objects of research are structurally similar elements of acoustical sandwich panels after a local repair of defects, such as through breakdown. The specimens were produced by serial technology from a fiberglass prepreg. Research was carried out using a universal electromechanical system Instron 5982 and servo-hydraulic system Instron 8801. For the analysis of the stress-strain state of the deformable elements the authors used the non-contact three-dimensional digital optical system Vic-3D, the mathematical apparatus which is based on the method of digital image correlation (DIC). To control the internal geometry of the specimen and assess the possible defect inspection infrared thermal imaging system FLIR SC7000 was used. The techniques of joint use of testing and measuring systems under static and cyclic tests were offered. For comparison, the repaired sandwich panel specimens were tested in tension and in tension under a preliminary cyclic loading with the registration of the deformation fields and thermal images. Their deformation and fracture mechanisms are analyzed, and their loading diagrams are obtained. The experimental data was obtained from the Vic3d system study of the evolution inhomogeneous fields of axial and transverse deformation on the surface of repaired sandwich panels under static loading and cyclic tests. By using infrared thermal imaging system internal structure, processes of the defects development and the temperature distribution on the surface of the test specimen were detected.

Sound Transmission Loss of a Panel Backed by a Small Enclosure

Sound transmission loss (STL) tests of acoustic insulation panels are commonly performed in large reverberation rooms. Large size rooms are required by acoustic standards to ensure that a large number of modes can be excited in the frequency range of interest, to create a diffuse sound field. However for STL measurements in low frequency range small enclosures should be able to provide adequate homogenous sound fields, namely ‘pressure sound fields’. The expected effect of the air sealed in an enclosure backing a panel, is to increase the stiffness of the panel artificially raising the first natural frequency of the panel, which corresponds to a minimum value in the STL spectrum. In this paper the influence of the air cavity's added stiffness on the panel STL is investigated in detail. As expected the effect of the sealed air is to increase the plate stiffness and as a result to increase the frequency of its first natural mode, however the effect on the STL in this frequency region is unexpectedly insignificant which removes the need for correcting STL measurements using small enclosures in low frequency range-around their first natural frequency of the panels.

Tunable two-dimensional acoustic meta-structure composed of funnel-shaped unit cells with multi-band negative acoustic property

This paper presents a two-dimensional heat-exhaust and sound-proof acoustic meta-structure exhibiting tunable multi-band negative effective mass density. The meta-structure was composed of periodic funnel-shaped units in a square lattice. Each unit cell operates simultaneously as a Helmholtz resonator (HR) and an extended pipe chamber resonator (EPCR), leading to a negative effective mass density creating bandgaps for incident sound energy dissipation without transmission. This structure allowed large heat-flow through the cross-sectional area of the extended pipe since the resonance was generated by acoustic elements without using solid membranes. The pipes were horizontally directed to a flow source to enable small flow resistance for cooling. Measurements of the sound transmission were performed using a two-load, four-microphone method for a unit cell and small reverberation chamber for two-dimensional panel to characterize the acoustic performance. The effective mass density showed significant frequency dependent variation exhibiting negative values at the specific bandgaps, while the effective bulk modulus was not affected by the resonator. Theoretical models incorporating local resonances in the multiple resonator units were proposed to analyze the noise reduction mechanism. The acoustic meta-structure parameters to create broader frequency bandgaps were investigated using the theoretical model. The negative effective mass density was calculated to investigate the creation of the bandgaps. The effects of design parameters such as length, cross-sectional area, and volume of the HR; length and cross-sectional area of the EPCR were analyzed. To maximize the frequency band gap, the suggested acoustic meta-structure panel, small neck length, and cross-sectional area of the HR, large EPCR length was advantageous. The bandgaps became broader when the two resonant frequencies were similar.

Fluid‐Porous‐Media Interaction: A Decoupled Solution Algorithm via Localised Lagrange Multipliers

AbstractFluid‐porous‐media interaction (FPMI) refers to a surface interaction among several non‐overlapping subsystems, composed of either a bulk fluid or a porous medium. This could be the interaction of blood with a blood vessel wall, a body of water with an earth‐dam structure, or acoustic waves with acoustic panels used in soundproofing, etc. These are highly coupled phenomena inheriting different coupling mechanisms which take place within the interacting subdomains as well as across common boundaries. Consequently, the mathematical models of such phenomena also consist of sets of coupled differential equations, which are commonly solved numerically, following a monolithic or a decoupled approach. Here, the focus is on the latter.The design of an algorithm for the decoupled solution of the fluid‐porous‐media‐interaction problem can be advantageous in several ways. First and foremost, the process of decoupling breaks down the problem into several subproblems, which can be solved efficiently employing specialised fluid and porous‐media solvers. Furthermore, solution of several decoupled subproblems instead of one highly coupled problem may be more economical in terms of computational costs. This is especially the case if the scheme permits parallel treatment of the produced subproblems.Here, the applicability of using the method of localised Lagrange multipliers for a partitioned solution of the problem of FPMI in the 2‐dimensional space is demonstrated. In this regard, the concept of modified Eulerian description for studying the motion of fluid bodies within moving boundaries is introduced. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Subwavelength acoustic metamaterial panels for underwater noise isolation

Acoustically thin metamaterial underwater noise isolation panels have been developed that provide as much as 16 dB of noise isolation for a panel with a thickness just 160th of the wavelength in the host medium (fresh water) at 2.5 kHz. The panels are composed of thin layers of neoprene rubber and polyoxymethylene containing air-filled voids. The level of isolation provided by the panels is shown to correlate positively with the volume fraction of air voids within the panel.

Preliminary evaluation of the sound absorption coefficient of a thin coconut coir fiber panel for automotive applications

Absorbent materials are fibrous or porous and must have the property of being good acoustic dissipaters. The noise reduction process occurs due to transformation of a part of the sound energy into heat. This process occurs when a sound wave propagates through pores or irregular arrangement of fibers. Sound propagation causes multiple reflections and friction of the air present in the absorbent medium transforming sound energy into heat. The acoustic surface treatment with absorbent material are widely used to reduce the reverberation in enclosed spaces or to increase the sound transmission loss of acoustic panels. In addition, these materials can also be applied to acoustic filters with the purpose to increase their efficiencies. The sound absorption depends on the excitation frequency of the sound and it is more effective at high frequencies. Natural fibers such as coconut coir fiber have a high potential to be used as sound absorbing material. Natural fibers are agriculture waste, manufacturing this fiber is a natural product, therefore an economic and interesting option. This work compares the sound absorption coefficient of a thin coconut coir fiber panel in relation to a composite panel made of fiberglass and expanded polyurethane foam used in the automotive industry. The evaluation of sound absorption coefficient was carried out with the impedance tube technique.

Reducing hospital noise with sound acoustic panels and diffusion: a controlled study

Noise has been identified as a major stressor in hospitals,1 ,2 with ambient noise frequently exceeding recommended levels set by the WHO3 and reportedly as high as alarm clocks.4 ,5...

A Study on Absorption Coefficient of Sustainable Acoustic Panels from Rice Husks and Sugarcane Baggase

Noise has detrimental effects on human lives and it is a nuisance to the environment. As many of the available sound reduction materials in the current market are hazardous, there are demands for alternative sustainable materials to reduce the noise problem. Therefore, the aim of this research is to study the potential of using an agricultural waste as sound absorption panel. For the purpose of this study, the combination of two materials was under studied; rice husks and sugarcane baggase. There were two main objective of the research; first is to develop absorption panels from the combination of rice husks and sugarcane baggase at different percentage of mixture. Second objective is to identify the absorption rate of the panels. The study encompasses the fabrication of the sustainable sound panels using the rice husk and sugarcane fibre and bond using Phenol formaldehyde (PF). Five panels of sized 12 inch x 12 inch and 12 mm thick were fabricated. The absorption coefficient of the samples was done at the acoustic lab, Faculty of Engineering & Build Environment, Universiti Kebangsaan Malaysia (UKM), Bangi. The panels were tested using an impedance tube. The procedure of the test was carried out in accordance with ISO 10534-2:1998 standards. Based on the results, sample 1 gave the highest absorption coefficient compared to sample 2, 3, 4 and 5. It can be concluded that the acoustic panel made from a mixture of 100% rice husks had higher absorption co-efficient compared to the performance of the other samples given the fact that the characteristic of the rice husks which has air gap in every single piece of rice husk. The spongy properties of the sample 1 panel has created many void spaces which encouraged more sound absorption capability due to the porous surface of the panel. Sound absorption is very much affected by the availability of porosity level of the panel. Thus, further studies on other potential materials from waste should be conducted.Keywords. Noise, Agriculture waste, sound, absorption panels, absorption co-efficient

A Preliminary Study on Acoustical Performance of Oil Palm Mesocarp Natural Fiber

As the population increases, the demand of a comfortable environmental such as sound pollution is getting higher. Sound pollutions also have become worsen and creating concerns for many peoples. Due to this problem, synthetic materials as acoustic absorbers still applied as commonly acoustical panels and this material may hazardous to human health and contribute significantly a pollution to the environments. However, researchers have interested in conducting their research on natural fiber to be an alternative sound absorber. This study investigated the potential of oil palm Mesocarp fiber for sound absorbing material. The Mesocarp fibers were mixed with polyurethane (PU) as binder with ratio of 70:30. The thickness was varied in 10mm, 20mm, 30mm, and 40mm. This study also investigated the air gap of 5mm and 10mm in the sound absorption performance. Impedance Tube Method was used to measure sound absorption coefficient (a). The measurement was done on accordance with ASTM E1050-98, which is the standard test method for impedance and absorption of acoustical materials using a tube. The results showed that the optimum value for Mesocarp fiber is 0.93. The optimum value obtained at 5000 Hz. The influence of air gap increases the sound absorption especially from 250 Hz to 4000 Hz. These results indicate that fiber from Mesocarp is promising to be used sound absorbing material.

Low-cost redesign of a music rehearsal space for high school ensembles

This presentation describes the redesign of an existing multi-purpose practice room used by high school concert bands, drumlines, and choral groups. Resource and cost restrictions limited the redesign and evaluation process for surface finishes only. The existing space had minimal early reflections and reverberation due to copious amounts of thick acoustic wall panels, resulting in a dead sound for choral and band use. The biggest challenge was to reposition the wall panels by distributing them in a checkerboard pattern, thereby balancing them with the reflective surfaces of the painted cinderblock underneath. In addition, one third of the absorptive suspended ceiling tile was replaced with 5/8” gypsum panels, and one third of the ceiling tile was removed altogether in order to couple the interstitial space above the suspended ceiling and increase the effective volume of the space. Odeon was used to create auralizations of various configurations by convolving anechoic recordings of a snare drum with the c...