Acoustic Panels Research Articles

Laser processing of composite materials for acoustic applications

The consistency of machined components in terms of their final material surfaces is a fundamental aspect of manufacturing. Laser-based non-contact sensors that use non-destructive speckle imaging are challenging the surface profilometry technique as an alternative method for the analysis of surface quality. This paper presents research into the importance of laser techniques in analyzing the surface roughness of composite materials used in the fabrication of acoustic panels. Roughness analyses performed by both the designed laser sensor and the surface profilometry technique were both found to be efficient; however, the speckle imaging method produces better results for most materials. Enhancements in surface roughness were measured and found to be 20% greater than those observed by the stylus method; in addition, the laser technique has low costs for commercial applications while being a scientific-concept-based analytical technique that uses a novel approach. The surface roughness was measured under different conditions by varying the speckle contrast using different positions and laser source orientations. The interactions between photons and phonons were analyzed in depth for a fabricated biomaterial-based-composite to assess its suitability for acoustic applications in different smart devices.

Material extrusion additive manufacturing of multifunctional sandwich panels with load-bearing and acoustic capabilities for aerospace applications

Reducing the noise produced by airplane engines is a significant challenge for the aerospace industry. In the present work, we investigate the design and fabrication of an acoustic sandwich panel featuring wider sound-absorbing performance compared to the currently employed technologies (e.g., perforated honeycomb cell sandwich panels). The use of material extrusion additive manufacturing (MEAM) enables us to create panels in one manufacturing step with complex geometry. The developed multifunctional (i.e., mechanical and acoustic) sandwich panel, which is based on the combination of five Helmholtz resonators, demonstrates an absorption spectrum over 517 Hz when measured with an impedance tube. The developed acoustic design, named Trapezoidal Compact (TC) sandwich, has an acoustic spectrum with more than 90% of absorption, comprised between 643 Hz and 1160 Hz. Three-point bending tests revealed that the stiffness of the sandwich panels with the TC geometry is up to ∼10% higher than those of the panels with a standard hexagonal honeycomb (HC) structure, additively manufactured with the same mass and wall thickness. The design developed in this work will contribute to the improvement of additive manufacturing process of multifunctional structures for aerospace applications.

Desert cotton and areca nut husk fibre reinforced hybridized bio-benzoxazine/epoxy bio-composites: Thermal, electrical and acoustic insulation applications

Due to increasing environmental concerns, significant attention has been gained for seeking out alternative sources for deforestation and to reduce as much as possible for the utilization of petroleum-based chemicals. In the present work hybrid bio-composites have been developed using epoxy resins (DGEBA-isophoronediamine and DGEBA-phenalkamine) and hybridized blend of bio-based cardanol-diaminodiphenylmethane (C-ddm) benzoxazine and DGEBA-isophoronediamine (bio-benzoxazine: epoxy resin 50:50 wt%)reinforced with desert cotton (DC) and areca nut husk fibres (ANF) separately under appropriate experimental conditions, in order to utilize them for high performance thermal, electrical and acoustic insulation panel applications. Mechanical behaviour, thermal conductivity, thermal resistance, electrical surface resistivity, electrical volume resistivity, sound absorption coefficient and sound transmission loss were studied as per standard methods. Results obtained from different studies infer that hybrid blended cardanol benzoxazine composite panels reinforced with desert cotton sandwich areca nut husk fibre (DC-sw-ANHF) possess appreciable thermal resistivity and electrical volume resistivity and the corresponding values are 0.22141 M2 k/w, and 1.888 × 1010 Ω, respectively. Data obtained from acoustic studies, indicate that all the fibre reinforced composites possess more than 0.7 value of sound absorption coefficient at 6400 Hz. The composite panel specimens developed using both desert cotton, and areca nut husk fibre reinforced with hybridized blend of bio-benzoxazine/epoxy resin can be used as insulation materials in the field of building construction.

Sound transmission loss of a novel acoustic metamaterial sandwich panel: Theory and experiment

A novel acoustic metamaterial (AMM) sandwich panel with enhanced sound transmission loss (STL) is proposed and designed by periodically distributing the local resonators in the stiffened core. The vibro-acoustic coupling is considered by the continuity of velocity at the fluid–structure interfaces. The effective dynamic mass density method is used to investigate the influences of the local resonators on the reinforced STL of the sandwich panel. The space harmonic expansion method and the virtual work principle are applied to derive the dynamic equations. An acoustic experiment is carried out and compared with the theoretical result. Experimental and theoretical results show that the STL curve has a peak near the objective frequency of the local resonator. The vibro-acoustic behaviors are further investigated using the finite element method (FEM). The peaks and dips in the STL curves are explained by the vibration modes and stress distributions obtained by the FEM. The proposed AMM sandwich panel possesses improved sound insulation performance around the mass-air-mass resonance frequency. For specific working conditions, the present method can be used to improve the STL of sandwich plates by adding resonators.

Improvement of the acoustic and mechanical properties of sponge ethylene propylene diene rubber/carbon nanotube composites crosslinked by subsequent sulfur and electron beam irradiation

AbstractIn this research, sponge ethylene propylene diene rubber (EPDM) nanocomposites based on functionalized multi‐walled carbon nanotubes (f‐MWCNTs) and foaming agent azodicarbonamide (AZD) were successfully fabricated as potential acoustic‐absorbing foams. Two crosslinking systems were utilized for stabilizing the foam structure and improving its properties by subsequent sulfur and electron beam irradiation at 50 kGy as a fixed dose. The impacts of the concentration of AZD, f‐MWCNTs and crosslinking systems on acoustic and physico‐mechanical properties were investigated. The results manifested that the optimum foaming content was 3 phr. The acoustic data exhibited satisfactory enhancement in the sound absorption coefficient (α) for irradiated foam nanocomposites compared to unirradiated nanocomposites. This was attributed to the barrier effect of f‐MWCNTs in reducing the pore size of the foam, leading to an increase in the tortuous path in the foam matrix that stifled the sound waves from transferring into the bulk. Likewise, the compression properties were also improved. However, tensile stress and strain at break values for irradiated foams relatively decreased. The data obtained revealed an excellent possibility of using these EPDM foam nanocomposites for potential applications such as acoustic panels and airborne sound insulation. © 2022 Society of Industrial Chemistry.

Mechanical and acoustical evaluation of bio-based composites made of cork granulates for acoustic ceiling tiles

This work is a study about new acoustic panels made of cork granulates coming from stopper by-products to be used as acoustic ceilings tiles, providing a sustainable and environmentally friendly alternative to traditional building materials. Cork granulates were bonded with water-based epoxy and acrylic resins. The obtained panels were acoustically and mechanically tested. The results showed values of sound absorption coefficient close to 0.50 and acceptable flexural strength for their use as suspended ceiling tiles. Therefore, these bio-based panels could be used as an alternative product to the traditional materials used for noise control applications inside commercial spaces like closed entertainment areas.

Experimental Characterization and Acoustic Correction of a Multipurpose Performance Hall: The Italian Theatre “Cavallino Bianco”

This study presents the retrofit acoustic dq1esign of the Italian theatre “Cavallino Bianco”. In its historical configuration, the hall had a curved roof with a pressed-plant fiber ceiling, which was demolished and replaced with a wooden roof without a false ceiling, leading to an increase in volume and a worsening of the reverberation time. This study proposed the realization of a wave ceiling and the application of sound-absorbing and reflecting panels on the walls, which have already been implemented. These modifications have affected the acoustic characterization of the theatre, as shown both through on-site measurements during the main construction phases and through numerical simulations. The reverberation time, clarity index, and speech transmission index (STI) are evaluated considering all the variations in the hall over different construction times, and the optimal solution is identified with regard to different specific uses. The final configuration with the new roof, by reducing the volume of the hall and using sound-absorbing materials, significantly reduces the reverberation time (e.g., at 2000 Hz, this reduction is from 2.33 to 1.47). In addition, the hall at full capacity with chairs and people shows evident improvement in terms of the clarity index, allowing the theatre to be used for a wide range of musical genres such as instrumental, symphonic, and opera performances. As regards the Combos 00 (concrete roof without vertical sound acoustic panels) and 01-a/b/c (wooden roof with draped curtains), the STI values are never lower than 0.42 and never higher than 0.70; therefore, the room never experiences poor or excellent conditions at any point. The Combos 01-a and 01-b, which have a non-performing C80, have a good STI index, confirming the difficulty of achieving a configuration that can be optimal a variety of uses. Combo 01 (wooden roof without vertical sound acoustic panels and no draped curtains), which has a good C80 value, presents a lower STI value, with an average performance. The STI values of Combo 02-a (characterized by wave false ceiling and vertical sound acoustic panels) are never lower than 0.52 and never higher than 0.60; therefore, neither poor nor excellent conditions are experienced in the room, but there is still a slight improvement over the combos 00 and 01.

Recycling Surgical Mask as Acoustic Panel using Hand Lay-Up Methods

The research was conducted to recycle surgical masks as acoustic panels using hand lay-up methods and to test their effectiveness in reducing noise using the tube method. The frequency used as a sound source is 495 Hz. Tests were carried out with variations in panel thickness, they are 1 cm, 2 cm, 3 cm, 4 cm, and 5 cm and three variations composite material, they are first layer, second layer and third layer of surgical mask. The panel test results show that the thicker acoustic panels are more effective in reducing noise based on the regression analysis that show the thicker panel from three variations composite material is 0.98, 0.99 and 0.96, respectively all of which are included in the very strong category. In addition, ANOVA analysis show that the thicker panels from all variation composite material respectively was 0.002, 0.001 and 0.009, they are showed the significant effect between the thickness of the panel and the effectiveness of the panel in reducing noise. Furthermore, based on the regression analysis from acoustic panels composite made of surgical masks from first layer, second layer and third layer were 8.24, 8.39 and 5.81, respectively the panel acoustic from second layer surgical masks are more effective to reduce the noise than other layer. Overall, it can be concluded that acoustic panels made of surgical masks are effective in reducing noise, as well as a solution to increasing surgical mask waste during the Covid-19 pandemic.

A Study on the Sound Absorption Properties of Mycelium-Based Composites Cultivated on Waste Paper-Based Substrates.

Mycelium-based composites have the potential to replace petrochemical-based materials within architectural systems and can propose biodegradable alternatives to synthetic sound absorbing materials. Sound absorbing materials help improve acoustic comfort, which in turn benefit our health and productivity. Mycelium-based composites are novel materials that result when mycelium, the vegetative root of fungi, is grown on agricultural plant-based residues. This research presents a material study that explores how substrate variants and fabrication methods affect the sound absorption properties of mycelium-based composites grown on paper-based waste substrate materials. Samples were grown using Pleurotus ostreatus fungi species on waste cardboard, paper, and newsprint substrates of varying processing techniques. Measurements of the normal-incidence sound absorption coefficient were presented and analyzed. This paper outlines two consecutive acoustic tests: the first round of experimentation gathered broad comparative data, useful for selecting materials for sound absorption purposes. The second acoustic test built on the results of the first, collecting more specific performance data and assessing material variability. The results of this study display that cardboard-based mycelium materials perform well acoustically and structurally and could successfully be used in acoustic panels.

Investigation and evaluation of the performance of interior finishing panels made from denim textile waste

The problem of textile waste is obvious and relevant, and detailed research into the problem is still lacking. In particular, there is a lack of research on the recycling and reuse of textile waste in such areas as the construction industry. The aim of this research is to develop an interior finishing panel by combining denim textile waste with an eco-friendly binder, to investigate, analyze and evaluate the main physical–mechanical properties of this panel. The investigated panels were made from denim textile waste with different structures for interior decoration. The results have shown that different manufacturing methods provide different sound insulation, and better sound insulation properties were distinguished by a panel made from fabric threads. When assessing the surface hardness of the panels, it was found that a panel made from threads has a higher hardness than a panel made from fabric scraps. Thus, evaluating the results of the performed research, it can be seen that the use of textile waste in acoustic panels is possible, with textile waste as the main component. Scanning electron microscopy analysis confirmed that the strength properties of the panel are closely related to the technology and structure of the panel, and that panels made from scraps have poorer strength and acoustic properties than panels made from threads.

Corn Cob Absorption Rate As Acoustic Material

Reducing CO2 emission through innovation discovery is essential to respond to the global warming issue. The research states that construction material contributes 11% of CO2 emission on building. Agricultural waste in Indonesia is plentiful, but it has not been used optimally, one of examples is corncob waste. The study to theoretically identify the absorption level on acoustic panel of corncob waste using two kinds of panel thickness dimensions composed of natural corncob through literature study and laboratory test of impedance tube by identifying the absorption panel coefficient phenomenon of corncob waste. The physical characteristic of corncob is porous, and this study found that there was a good absorption level in two dimensions of panel thickness of 3 cm and 5 cm. It was strengthened by the finding of a frequency shift phenomenon of two dimensions of panel thickness due to resonance in air cavity/gap among corncobs.

Evaluation and optimization of acoustics of a multipurpose room to improve speech intelligibility

The work presented in this paper was conducted as part of a student project in a senior course on Noise Control at Tennessee Tech. The project involved improving the acoustics of the multipurpose room in the university student center. There were repeated concerns regarding the poor acoustics conditions related with speech and intelligibility caused by excessive reverberations in the room. In order to solve this issue, an examination of the complete sound field in the room including reverberation time have been investigated with the aim of proposing solutions to improve the acoustics for future use. The evaluation of the room was done with both software simulation and experimental data obtained from on-site visit measurements. A comparison between the simulated and experimental data is presented and served as the basics for the analytical solutions necessary for acoustic optimization. Furthermore, renderings of possible mounting locations of acoustic panels with their specification have been provided based on the commercially available panels and cost consideration.

Controling noise from tunnel ventilation fans

Infrastructure projects involving transportation networks underground such as railways and roadways have strict ventilation requirements for fire and smoke and engine exhaust control. The fans used for these projects are often very large and very loud compared to typical building equipment. Transit autorities typically have criteria regarding A-weighted decibel levels in and around the tunnel environment to ensure audibilty of emergency announcements and acceptablility of environmental sound levels. Fan and duct silencers as well as acoustical panels play critical roles in meeting maximum sound level criteria at property lines and at track and platform levels. Due to high airflow rates, the design, placement, and configuration of noise control products must be carefully considered to ensure adequate system performance. This paper will review various issues and considerations encountered in tunnel ventilation noise control projects and present typical solutions and design practices with examples.

Acoustic Performance of Sound Absorbing Materials Produced from Wool of Local Mountain Sheep.

Wool of mountain sheep, treated nowadays as a waste or troublesome byproduct of sheep husbandry, was used for the production of sound-absorbing materials. Felts of two different thicknesses were produced from loose fibres. Additionally, two types of yarn, ring spun and core rug, were obtained. The yarns were used for the production of tufted fabric with cut and loop piles. During the examinations, basic parameters of the obtained materials were determined. Then, according to standard procedure with the use of impedance tube, the sound absorption coefficient was measured, and the noise reduction coefficient (NRC) was calculated. It was revealed that felt produced from coarse wool exhibits high porosity, and its sound absorbing capacity is strongly related to the felt thickness. For thicker felt the NRC achieved 0.4, which is comparable with the NRC of commercial ceiling tiles. It was shown that the crucial parameter influencing the sound absorption of the tufted fabrics was the pile height. For both types of yarns, when the height of the pile was increased from 12 to 16 mm, the NRC increased from 0.4 to 0.42. The manufactured materials made from local wool possess good absorption capacity, similar to commercial products usually made from more expensive wool types. The materials look nice and can be used for noise reduction as inner acoustic screens, panels, or carpets.

Case study: Acoustical design for newly renovated behavioral health suite

This presentation addresses requirements and opportunities for the acoustical design of a behavioral design suite. Examples of coordinated design elements will be presented from a recent remodel project for a single suite in the UCSF Langley Porter Psychiatric Hospital and Clinics Mt. Zion relocation. The following will be presented. Unique components: Equipment transcranial magnetic stimulation (TMS) is a noninvasive procedure that uses magnetic fields to stimulate nerve cells in the brain, used to address depression. TMS therapy treatment equipment has a loud tapping noise that can be highly annoying to occupants of adjacent rooms. Sound isolation and sound-absorbing treatments are important design elements for a room with this equipment. Unique requirements: Patient safety behavioral health suites have unique patient safety requirements that led to the design selection for acoustical tamper-proof ceiling panels and specializd door gaskets at specific room types. Design considerations: Group therapy room group therapy rooms are in-patient areas that can consist of small and large groups, sometimes involving simultaneous group activities among patients and staff. HIPAA requirements, speech intelligibility, and occupant comfort, as well as hospital operations were important considerations for the coordinated acoustical design.

Mechanical, thermal and acoustical evaluation of biocomposites made of agricultural waste for ceiling tiles

This work deals with experimental research about acoustic panels made of agricultural waste to be used as ceiling tiles, providing a sustainable and environmentally friendly alternative to traditional building materials. The raw materials used in this work were rice husk, vine pruning residues, cork (white cork, virgin cork, and expanded cork), and prickly pear. All of them were bonded with a water-based acrylic resin in different proportions. The obtained panels were mechanically, thermally and acoustically tested. The flexural and the dynamic modulus of elasticity, as well as other important physical properties, such as open porosity, tortuosity or flow resistivity, and thermal conductivity, were obtained. The sound absorption coefficient of the biocomposites was experimentally measured, using an impedance tube, and modeled, using the Zwikker and Kosten model, over the frequency range from 200 Hz to 6400 Hz. The results showed values of sound absorption coefficients close to 0.80 and acceptable flexural strength for their use as suspended ceiling tiles. Therefore, these new categories of biocomposites provide sustainable bio-based materials that can be an alternative to the traditional acoustic ceiling panels, mainly composed of synthetic fibers or foams and petroleum-based resins.

Development of 100% Recycled Thermoplastic Composites for Sound Insulated Acoustic Panels

Today, environmental problems are increasing rapidly and the focus is shifting to seeking long-term and sustainable solutions. At this point, the economical use of raw material resources is important and this makes recycling a necessity, not a diversity. In this context, environmentally friendly acoustic panels are designed with composites produced by recycling 100% textile and packaging wastes for the noise problem in buildings. Denim fabrics from textile wastes and low-density polyethylene bottle caps from packaging wastes are used. Denim fabrics that are shredded into cotton fibers are blended with ground waste polyethylene granules and porous structures are obtained with the hot press technique. The panels, whose physical and acoustic properties have been tested, are aimed to create an environmentally friendly alternative to existing products.

The fire-safe application of acoustic materials in cultural and entertainment buildings

Introduction. In theatre and concert halls, acoustic environments are created, among other things, by wall and ceiling panels, that have special sound absorption properties. However, modern materials demonstrating the required acoustic properties do not necessarily comply with effective fire safety regulations.Aims and purposes. Modern acoustic panels, made of mineral fibers, are among the most effective ones in terms of sound absorption; they also provide wide opportunities for the high-quality design of auditoriums.Despite the non-combustible basic component, high acoustic performance of such decorative items is attained thanks to a set of supplementary materials that have different chemical compositions, structures, physical and mechanical properties, which, in the aggregate, slightly reduce fire safety.Due to the lack of fire safety requirements applicable to special materials that perform the function of sound absorption, their usability in auditoriums of buildings and structures is confirmed, as a rule, according to the standards that apply to traditional decorative and finishing materials. At the same time, the use of high-performance acoustic materials is problematic due to rather strict fire safety requirements for decorative and finishing materials designated for walls and ceilings.The purpose of this work is to conduct analytical studies on the effective regulatory framework of the fire-safe use of acoustic materials, perform comparative experimental studies on the assessment of their fire-technical characteristics to study the feasibility of drafting proposals on their acceptable use on the premises and in the halls of cultural and entertainment facilities.Results and discussion. Analytical studies were conducted to identify the most effective sound-absorbing finishing materials that feature lower fire hazards. They are mineral wool products made of glass fiber or stone wool. A set of fire hazard indicators, typical for acoustic decorative materials, made of mineral fibers, were subject to comparative experimental studies for the purpose of their legitimate fire-safe use in public auditoriums.The co-authors found that the requirements, applicable to acoustic materials designated for walls and ceilings, can be issued as amendments to effective regulatory and technical documents on fire safety.Conclusions. The co-authors proposed amendments to effective fire safety regulations in respect of the requirements applicable to acoustic materials designated for walls and ceilings of auditoriums.

Application of Epoxy Resin for Improvement of the Banana Stem- Acoustic Panel

Background: Greener epoxidation by using vegetable oil to create an eco-friendly epoxide is being studied because it is a more cost-effective and environmentally friendly commodity that is safer than non-renewable materials. The aim of this research is to come up with low-cost solutions for banana trunk acoustic panels with kinetic modelling of epoxy-based palm oil. Method: In this study, the epoxidation of palm oleic acid was carried out by in situ performic acid to produce epoxidized palm oleic acid. Results: Banana trunk acoustic panel was successfully innovated based on the performance when the epoxy was applied. Lastly, a mathematical model was developed by using the numerical integration of the 4th order Runge-Kutta method, and the results showed that there is a good agreement between the simulation and experimental data, which validates the kinetic model. Conclusion: Overall, the peracid mechanism was effective in producing a high yield of epoxy from palm oleic acid that is useful for the improvement of acoustic panels based on the banana trunk.

ARTISTIC ACOUSTIC PANEL RECYCLED MATERIAL FROM PLASTIC BOTTLES AND WASTE OF SAMPYAN, SAWDUST, HUSKS, STRAW

Background – The problem of waste is one of big problems arise from various sectors. Recycling and reusing can be one good solution. Balinese people who still carry out traditions including the event with various arts, one of which is a beautiful offering. This beautiful offering is in the form of sampyan from art coconut leaves which ends as waste. In the past, when Balinese were going to cook, they could use fuel from this dry coconut leaves waste. On The Holidays for ceremonies, there is a 30% increase in waste. Even though this is a ceremonial waste, a balance in the relationship with God/Hyang Widi must be maintained in accordance with the Balinese concept of Tri Hita Karana. This concept is in the form of a balanced relationship towards Hyang Widi/God, to the fellow humans and to the environment that causes happiness. Therefore, waste must be processed. Husks and straw waste from rise field in Bali amounted to 54.65 million tons of GKG, then alot of sawdust waste from wood carving and wood architecture industries. This waste is often burned even though some are used for planting media and fuel. On the other hand, the tourism community and people in Bali produce 829 tons of plastic waste per day. Currently, appreciation of buildings with “Green Architecture” is a concern for tourism and will become of destinations. Thus, it will very possible in Bali. Purpose – provide economic value added for the community, wood workers and farmers and make the world a better place. Findings –Artistic acoustic panel recycled material from plastic bottles and waste of sampyan, sawdust, husks, straw. Originality/value – Acoustic Panel Material and Artistic Acoustic Panels with Balinese Architectural Ornaments is an original. Design/methodology/approach – Recycled plastic waste with the right mixture composition is heated and printed with a hot press machine. In this study, the Transmission Loss test was carried out using an Impedance Tube. Research limitations – Measurement of transmission loss on sheet panels has limitations. Measurements should be developed into room research.