• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.1071-1076
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• 2002

The purpose of this paper is to examine sound absorption characteristics of sintered Al(aluminum) plate. Comparison between experiment and theoretical analysts by using empirical formula are made. Based on comparison. it is found that Voronina model gives more reasonable explanation for sound absorption characteristics of sintered Al plates. Effect of air gap with varying the thickness of plates are also investigated, which concludes that the air gap generally increase absorption but for too thick thickness of Al plates. Al plates with air gap shows 0.85∼0.9 of NRC(Noise Reduction Coefficient) measured in reverberation room. which is comparable to glass wool. Comparison between normal and random Incident absorption shows that random incident absorption is higher than normal incident absorption.

• Journal of the Korean Wood Science and Technology
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• v.50 no.5
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• pp.365-374
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• 2022

Today, commercialized Hinoki cypress cubes are used for fragrance, humidification, and pillows in Korea. In this study, the sound absorption ability of Hinoki cypress (Chamaecyparis obtusa) cubes was examined. The three groups of Hinoki cypress cubes were prepared depending on their dimension (L: 9 × 9 × 9, M: 7 × 7 × 7, S: 4 × 4 × 4 mm). Their sound absorption coefficient was examined after filling 6, 8, 10, and 12 cm height in impedance tubes, respectively. Overall, the sound absorption ability depending on dimension was superior in the M group compared to the L and S groups. Also, as the filling height increased, the sound absorption capacity increased. In sum, noise reduction coefficients (NRC) of all Hinoki cypress cubes were 0.41-0.59. Thus, this research found that Hinoki cypress cubes have a sound-absorbing function.

• Journal of the Korean Wood Science and Technology
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• v.47 no.5
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• pp.644-654
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• 2019

In this study, the gas permeability, sound absorption coefficient, and sound transmission loss of the Paulownia tomentosa wood were estimated using capillary flow porometry, transfer function method, and transfer matrix method, respectively. The longitudinal specific permeability constant of the Paulownia tomentosa wood with a thickness of 20 mm was 0.254 for the control sample and 0.279, 0.314, and 0.452 after being subjected to heat treatments at $100^{\circ}C$, $160^{\circ}C$, and $200^{\circ}C$, respectively. The gas permeability was observed to be slightly increased by the heat treatment. The mean sound absorption coefficients of 20-mm thick Paulownia tomentosa log cross-section for the control sample and after being subjected to heat treatments at $100^{\circ}C$, $160^{\circ}C$, and $200^{\circ}C$ were 0.101, 0.109, 0.096 and 0.106, respectively. Further, the noise reduction coefficients of 20-mm thick Paulownia tomentosa log cross-section of the control sample and after being subjected to heat treatment at temperatures of $100^{\circ}C$, $160^{\circ}C$, and $200^{\circ}C$ were 0.060, 0.067, 0.062 and 0.071, respectively. The mean of sound transmission loss of the 20-mm thick Paulownia tomentosa log cross-section was approximately 36.93 dB. Furthermore, the gas permeability and sound absorption coefficient of the heat-treated Paulownia tomentosa discs slightly increased depending on the heat treatment temperature; however, the rate of increase was insignificant.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.4
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• pp.481-487
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• 2017

The purpose of this study is to develop the hybrid sound-absorbing materials that is made from organic polyurethane sponge impregnated with inorganic binder solutions. The inorganic slurry which is made from ${\alpha}$-hemihydrate gypsum mixed with 60% water, and various additives including plasticizer are used as binder. The test specimens are prepared and tested for sound absorption performance by the impedance tube methods. From the test results, noise reduction coefficient(NRC) of development materials specimen bound by the inorganic binder slurry is 0.41. They are 2 times or more higher than commercial products specimens bound by organic materials only which have NRC values in the range of 0.14 to 0.28. The polyurethane sponge specimens impregnated with inorganic gypsum slurry binder have a good balance between performance and cost, and have proper properties in density, thermal conductivity, non-combustible, and absence of harmful substances as sound-absorbing internal boards for noise barrier wall. It is apparent that the good sound absorption materials can be produced according to the optimum mix design that is recommended from this study.

• Journal of the Korea Institute of Building Construction
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• v.9 no.5
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• pp.63-70
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• 2009

This study is part of an ongoing research project on the development of a sound-absorbing lightweight foamed concrete manufactured by a hydro-thermal reaction between silica and calcium. As the silica source, pulverized bottom ash was used, and as several cementitious powders of ordinary portland cement, alumina cement and calcium hydroxide were used. Manufacture of foamed concrete was accomplished using the pre-foaming method to make a continuous pore system, which is the method of making the foam by using a foaming agent, then making the slurry by mixing the foam, water, and powders. The experiment factors are W/B, foam agent dilution ratio, and foam ratio, and test items are compressive strength, dry density, void ratio, and absorption rate, as evaluated by NRC. The experiment results showed that the sound absorption of lightweight foamed concrete satisfied NRC requirements for the absorbing materials in most of the experiments. It is thus concluded that foam ratio was the most dominant factor, and significantly affected all properties of lightweight foamed concrete in this study. W/B rarely affected total void ratio and continuous void ratio as well as compressive strength, and dry density and foam agent dilution ratio also had little effect onalmost all properties. The analysis of the correlation between NRC, absorption time, continuous void ratio, and absorption time showed that the interrelationship of the continuous void ratio was high.

• Journal of the Korean Wood Science and Technology
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• v.47 no.1
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• pp.33-39
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• 2019

The square timbers of larch having cross section of $90mm{\times}90mm$ were glued laterally to be formed $1,200mm{\times}2,400mm$ panels which were used as cores for CLT wall panels. Then, structural plywood panels having size of $1,200mm{\times}2,400mm$ were used as cross band covering the small square timber cores to manufacture CLT wall panels. The sound absorption rate of CLT wall panels and polyester board attached CLT wall panels were investigated. The mean sound absorption coefficients of the former and the latter in the frequency range of 100-6400 Hz were 0.21 and 0.74, respectively. The noise reduction coefficients (NRC) of those were 0.21 and 0.40, respectively. Also, the mean sound transmission loss of CLT wood panel in the frequency range of 50-1600 Hz was 45.12 dB and that value at the frequency of 500 Hz was 42.49 dB. It was suggested that the polyester board attached CLT wall panels could be used as housing wall because of its high sound absorption rate and high sound transmission loss.