Papers by Keyword: Sound Absorption

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Authors: Huai Qian Bao, Ning Zhang, Xue Gang Hou
Abstract: For the complexity of the internal microstructure of porous aluminum foam, on the basis of Rayleigh-Kirchhoff circular tube model, taking viscosity loss and thermal transmission, the paper establishes a simplified theoretical model for sound absorption properties of aluminum foam. The paper also calculates and analyzes the influence of Static flow resistance on the sound absorption properties in the rigidity and cavity backing. The results show that the peak frequency moves to lower with the increasing of the thickness of the air layer. What’s more, there is a direct corresponding relation between flow resistance and the best sound absorption frequency range of aluminum foam. In a reasonable range of flow resistance value, the capability of sound absorption reach optimal, Aluminum Foam won’t have fine sound absorption capability if the value of flow resistance is too big or small.
Authors: Elammaran Jayamani, Soon Kok Heng, Muhammad Khusairy bin Bakri, Sinin Hamdan
Abstract: This research focuses on the sound absorption coefficient of three different natural fibers reinforced epoxy composites. The natural fibers used are coconut coir, kenaf, and sugarcane bagasse. All of these fibers were mixed with epoxy resin and hardener with a ratio of 4:1. The mixtures were then poured into a circular mold and compressed by using compression molding technique. It was left for curing for 24 hours at standard room temperature. The results were obtained using the two-microphone transfer functions impedance tube method according to ASTM E1050-12. It is found that as the fiber loading increased, the sound absorption coefficient of the composites increased. 20wt% Coconut coir epoxy composites and 20wt% kenaf fiber epoxy composites have the highest sound absorption coefficient with almost similar sound absorption of 0.078 at 5000Hz. While, 20wt% sugarcane bagasse epoxy composites have sound absorption of 0.075 at 5000Hz.
Authors: Hak Bin Kim, Earl Han, Sung Woon Cha
Abstract: The microcellular foamed plastics (MCPs) have high material strength, a relatively small cell size, and a high cell density in comparison with conventional foamed plastics. In particular, the small size of cell in MCPs makes many applications possible in a range of fields. Its high reflectivity enables its application as a reflector that is a part of the back light unit in the LED industry. Thanks to its low density and high strength, MCPs can be used as diaphragm in speakers. They also have many other uses. MCPs show a noise suppression property which allows them to be used in the building industry. A soundproofing plate made of MCPs exhibits a better soundproofing property in comparison with a soundproofing plate made of ordinary plastic. In this study, the author manufactured a soundproofing plate using microcellular foamed polypropylene (PP) and assessed the properties of the absorbing and proofing sound. As a result, the findings showed the possibility of using MCPs as a soundproofing plate in the building industry.
Authors: Wei Hong Tan, Rosmaini Ahmad, Nur Hafizah Zunaidi, Ruslizam Daud, E.M. Cheng
Abstract: Fabrication of an impedance tube for measuring sound absorption coefficient is presented in this paper. Transfer-function method is chosen for the sound absorption analysis. The impedance tube is designed and fabricated in accordance with ISO 10534-2. The tube is made from brass with diameter of 114.3 mm and length of 1.42 m. It is designed for the frequency range 60 Hz to 1800Hz. Three microphone positions are installed to achieve the frequency range with a single tube. The theoretical background of transfer-function method between two microphones is discussed. Initially, impedance tube is characterized by the measurement without testing material in the tube. Micro-perforated panel (MPP) with 50 mm and 100 mm of cavity depth are used for measurement. The sound absorption coefficient measurement of the MPP is compared with theory and good agreement is achieved. Various problems related to design and construction is addressed and the optimal configuration is presented.
Authors: Xiang Yu Luo, Wen Fang Li, Xue Li Jin
Abstract: In this paper, the effect of ceramsite aggregate size and gradation on the sound absorption and mechanical properties of the materials were studied and the relationship between material’s pore structure and its sound absorption were discussed. It can be found from the results that the sound absorption and mechanical properties of the ceramsite sound-absorbing materials increase with the content of the fine ceramsite increased due to the decrease of the median pore diameter of the ceramsite sound-absorbing materials where the improvement of the sound absorption at the high frequency band is more significant suggesting that fine pores have a better sound-absorbing effect for high-frequency noise. Higher effective porosity doesn’t mean better sound absorption, because materials with coarse pores have shorter internal routes for sound waves and less friction during sound waves passing through pores, which conversely decreases the material’s sound absorption. Ceramsite with higher internal porosity and more uniform pore diameter distribution can produce materials with better sound absorption.
Authors: Wanlop Harnnarongchai, Kantima Chaochanchaikul
Abstract: The sound absorbing efficiency of natural rubber (NR) foam is affected by the cell morphology of foam. Potassium oleate (K-oleate) and sodium bicarbonate (NaHCO3) were used as blowing agents to create open-cell foam. Amounts of the blowing agent were varied from 0.5 to 8.0 part per hundred of rubber (phr) to evaluate cell size and number of foam cell as well as sound adsorption coefficient of NR foam. The NR foam specimens were prepared using mould and air-circulating oven for vulcanizing and foaming processes. The results indicated that K-oleate at 2.0 phr and NaHCO3 at 0.5 phr led to form NR foam with the smallest cell size and the largest number of foam cell. At low frequencies, the optimum sound adsorption coefficient of NR foam was caused by filling K-oleate 2 phr. However, that of NR foam at high frequencies was provided by 0.5 phr-NaHCO3 addition.
Authors: Elwaleed Awad Khidir, Nik Abdullah Nik Mohamed, Mohd Jailani Mohd Nor, Mohd Faizal Mat Tahir, Rozli Zulkifli, Mohd Zaki Nuawi
Abstract: An experimental study on the effect of panel density on the sound absorption properties of a date palm fiber panel has been presented in this paper. The experiments were carried out by using impedance tube at the Acoustic Lab, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia. The date palm fiber was tested for densities of 77 kg/m3, 100 kg/m3 and 125 kg/m3.The results show that the values of absorption coefficient improve when increasing the density of the panel. Noise reduction coefficient (NRC) was computed to compare the performance of the palm date fiber samples for the different densities. The NRC increases by increasing the density.
Authors: Noor Quratul Aine Adnan, Anika Zafiah M. Rus
Abstract: Biopolymer foam was prepared based on vegetable oil and Polyol Flexible (Epoxy) with commercial Polymethane Polyphenyl Isocyanate (Modified Polymeric-MDI) with the different proportion ratio. This research is to study the acoustic property between different proportion ratio of biomonomer and epoxy. The acoustic property of biopolymer foam was examined by using an impedance tube test according to ASTM E-1050 of sound absorption coefficient (α). Based on the result obtained, mostly the values of α were consistent at the samples F. It was observed that, sample F gave the highest value of α that is 0.997 at of 3500Hz. Sample F from ratio 100:0 from epoxy to biomonomer and gave the best sound absorption than the other foam. So, different ratio give different α at different frequency (Hz).
Authors: Muhd Hafeez Zainulabidin, M.H.M. Yusuff, Al Emran Ismail, M.Z. Kasron, A.S.M. Kassim
Abstract: This paper describes the investigation and analysis on two materials in which one material is a relatively good sound absorber at low frequency range and another is a relatively good sound absorber at high frequency range, combined together in layers to form a better sound absorber for a wider range of frequencies. The layer combinations of the materials are varied and the values of Sound Absorption Coefficient, α are measured experimentally by using impedance tubes with two microphones transfer function method according to ISO 10534-2 standard. The results obtained are compared in terms of the order of material and the number of layer combinations of materials for each sample. The orders of combinations and number of layers of combinations have significant influence on the sound absorption characteristics. The order of materials has reversed effect on Sound Absorption Coefficient, α as the number of layer combination is increased. Increase in the combination number will make the specimen performed relatively better at a wider frequency range.
Authors: Samson Rwawiire, Blanka Tomková, Jiří Militký, Lubos Hes, Bandu Madhukar Kale, Abdul Jabbar
Abstract: The desire to mitigate climate change due to greenhouse gas emissions has led to the exploration of plant fibers as alternative materials for various industrial applications acoustics inclusive. In this investigation, sound absorption properties of barkcloth, a nonwoven fabric from Antiaris toxicaria were characterized. Theoretical empirical sound absorption models based on Delany and Bazley such as Miki, Wu and Allard – Champoux were utilized to validate the experimental data. The empirical models were in agreement with experimental data; Incorporation of an air-gap between the fabric layers had a positive influence on the overall sound absorption behavior of barkcloth fabrics rendering the fabric a good sound absorption material.
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