• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1341-1346
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• 2001

In this study, the acoustic properties of steel-wire sound absorbing materials with different thickness and bulk density were investigated in terms of characteristic impedance, propagation constant, and absorption coefficient. The well-known two-cavity method was used for evaluating those acoustic parameter values in experiments. Also, in order to validate the experimentally measured values, the results were compared with the results obtained from Chung and Blaser's transfer function method and SWR method. The experimentally measured values of normal absorption coefficients were generally agreed well with the corresponding values from the transfer function method and the SWR method. Based on the experimental results, the following conclusions could be made. The magnitude of the absorption coefficient and the frequency range of the maximum absorption coefficient were controllable by changing the thickness and bulk density of the sound absorbing materials. Also, the magnitude of the absorption coefficient depended on the characteristic impedance and the propagation constant. As large as the air cavity depth at the rear side of the steel-wire sound absorbing materials, the maximum magnitude of the absorption coefficient occurred at the lower frequency ranges.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.5 s.98
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• pp.571-577
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• 2005

The acoustic absorption of multiple layer perforated panel systems is largely reduced at the anti-resonance frequency. In order to improve the acoustic absorption at the anti-resonance frequency, the sound absorbing materials are inserted between perforated panels. By the insertion of absorbing materials, it is found that the multiple layer perforated panel system has better acoustic absorption at the anti-resonance frequency and more broadband frequency. Besides, it is shown that the absorption coefficients from the transfer matrix method agree well with the values measured by the two-microphone impedance tube method for various combinations of perforated panels, airspaces or sound absorbing materials.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.5
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• pp.413-421
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• 2003

The acoustic performances of steel-wire sound absorbing materials with different thicknesses and bulk densities were investigated experimentally. The well-known two-cavity method was used to measure the characteristic impedance, propagation constant and absorption coefficient. The normal absorption coefficients measured by two-cavity method agreed well with those by the two-microphone impedance tube method. The experimental results showed that the magnitude of the absorption coefficient and the frequency range of the maximum absorption coefficient were controllable by changing the thickness and bulk density of the steel-wire. Therefore, the steel-wires obtained from the crushed tire chips could be used as a good absorbing material.

• Journal of the Korean Wood Science and Technology
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• v.46 no.2
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• pp.149-154
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• 2018

The changes in sound absorption capability and air permeability of Malas wood after high temperature heat treatment were investigated. The average air permeability of Malas in longitudinal direction after heated under the temperature of $190^{\circ}C$ during 3 hours was about 23.48 darcys and that of control was about 3.11 darcys. The noise reduction coefficients of Malas specimens were 17% for treatment and 10% for control. The means of sound absorption coefficient of specimens in the frequency range of 50~6,400 Hz were 42% for treatment and 17% for control, respectively.

• Structural Engineering and Mechanics
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• v.76 no.5
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• pp.613-618
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• 2020

Exhausting oil resources and increasing pollution around the world are forcing researchers to look for new, renewable, biodegradable materials to lead sustainable development. The use of fiber reinforced composites based on natural fibres has increasingly begun as prospective materials for various engineering applications in the automotive, rail, construction and aerospace industries. The natural fiber chosen to make the composite material is plant-based fibre, e.g. jute fibre, and hemp fibre. Thermosetting polymer based Epoxy (LY556) was utilized as matrix material and The composites were produced using hand lay-up technique. The fabricated composites were tested for acoustic testing, thermo-gravimetric analysis (TGA) and flammability testing to asses sound absorption, thermal decomposition and fire resistivity of the structures. Hemp fibre composites have shown improved thermal stability over Jute fibre composites. However, the fire resistance characteristics of jute fibre composites are better as compared to hemp fibre composites. The sound absorption coefficient of composites was found to enhance with the increase of frequency.

• 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.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.5
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• pp.429-436
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• 2012

In concert halls and auditoriums, acoustic reflector and stage enclosure is one of the main factors on the room and stage acoustic characteristics. As a stage enclosure and acoustic reflector honey comb based light-weight reflector is widely used, because it is easy to install. However, there was not enough research on the surface density effect on room and stage acoustics. In this study, sound absorption coefficient tests on three kinds of wooden acoustic reflectors with different surface density were conducted. Surface density of acoustic reflector was changed from 11 kg/$m^2$ to 41 kg/$m^2$. For the low frequency excitation, sub-woofer was used with omnidirectional loud-speaker simultaneously. From the experiments, it was found that sound absorption coefficient below 250 Hz band was decrease by the increment of surface density. In order to check the influence of the surface density on room and stage acoustic parameters, room acoustic simulation was conducted with sound absorption coefficients, which were tested in reverberation chamber. By the increment of surface density of acoustic reflector, RT(reverberation time) and EDT(early decay time) were increased. Also, ST(stage support) was improved in low frequency bands.

• Journal of the Korean Wood Science and Technology
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• v.38 no.6
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• pp.463-469
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• 2010

To suggest the practical use of fast growing tree, we estimated the physical and sound absorption properties of Cherospondias axillaris which is one of the japanese fast growing species. The average annual ring width and air dry specific gravity were 8 mm and 0.55 respectively. The sound absorption coefficients of Cherospondias axillaris wood generally seemed to be a little higher than those of other construction materials such as 6 mm thick gypsum board and 18 mm thick fiberboard, and considered that it could be used as a constructing material owing to relatively good mechanical properties and sound absorption properties.

• Journal of the Korean Wood Science and Technology
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• v.48 no.5
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• pp.631-640
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• 2020

In this study, the effect of specimen size and layer thickness on the sound absorption of the leaves of two evergreen broad-leaved tree species, Dendropanax morbiferus and Fatsia japonica, was investigated. The specimen sizes of 0.5 × 0.5, 1.0 × 1.0, and 2.0 × 2.0 ㎠ and layer thicknesses of 1.00, 1.75, and 2.50 cm were considered. At the layer thickness of 2.5 cm, the leaf of the D. morbiferus showed no significant difference in sound absorption coefficients (SACs) as the sample size varied, however, a significant change in SACs was recorded in that of the F. japonica. At 1.0-cm thickness, the SACs of the F. japonica leaf varied more remarkably with the sample size. The 2.50-cm-thick F. japonica leaf with the specimen size 0.5 × 0.5 ㎠ exhibited the highest sound absorption effect among all samples investigated.

• Journal of Environmental Science International
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• v.32 no.1
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• pp.25-35
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• 2023

The purpose of this study was to determine the optimal sound absorption conditions by comparing the sound absorption characteristics of fresh and air-dried leaves of Quercus glauca, the main species of evergreen broadleaf trees (EBLT) in southern Korea. The sound absorption coefficients (SACs) obtained under 18 conditions were comparatively analyzed. The SAC of air-dried leaves improved significantly with increasing leaf layer thickness. The highest average SAC in the fresh leaf group was 0.617, which was observed under the condition of a leaf specimen size of 0.5 × 0.5 cm² and a leaf layer thickness of 1.75 cm. In a group of air-dried leaves, this was 0.615 under the condition of a leaf specimen size of 0.5 × 0.5 cm² and a leaf layer thickness of 2.50 cm. The maximum value of SAC for each wavelength was observed under the condition of a leaf layer thickness of 2.50 cm consisting of 0.5 × 0.5 cm² leaf specimens, ranging from 1,400 Hz to 1,500 Hz.