• 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 Wood Science and Technology
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• v.38 no.6
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• pp.457-462
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• 2010

Sound absorption capability and bending strength of laminated ship-building plywood waste of maple and melanti wood were estimated. Sound absorption coefficients of wood had been measured by the two microphone transfer function method and bending strength examined by three point loading. The maximum strength in bending of laminated ship-building plywood waste of maple and melanti wood were 534 and 414 kgf/$cm^2$, respectively. The sound absorption coefficients of laminated ship-building plywood waste were higher than mongolian oak and fiber board, well used construction material. Especially, in the case of laminated ship-building plywood waste of melanti wood, average sound absorption coefficient was about 0.25. It was surmised that the laminated ship-building plywood waste can be used as interior materials because of its good mechanical and sound absorption properties.

• Journal of the Korean Wood Science and Technology
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• v.40 no.4
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• pp.237-243
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• 2012

Sound absorption capability and anatomical features of the organosolv pretreated Japanese larch and yellow poplar wood were estimated by stereoscopic observation and two microphone transfer function method. Sound absorption capabilities of organosolv treated wood, in the entire estimated frequency range (50~6,400 Hz), were higher than those of control specimen. Especially, the treated wood's absorption capabilities measured in the frequency range of 2~4 kHz were about two times higher than those of control specimen. By the organosolv pretreatment (at $70{\sim}120^{\circ}C$), the weight loss of wood occurred in less than 1% of total weight of wood and the porosity of wood increased slightly. In addition, it was presupposed that microstructural changes of wood occurred during organosolv pretreatment and this structural changes cause the increasing of the sound absorption capability of wood.

• Journal of Power System Engineering
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• v.12 no.4
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• pp.46-51
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• 2008

Honeycomb panel has a constructive advantage because it is constructed with a honeycomb core, so it has relatively higher strength ratio to weight. Therefore honeycomb panel has been used as the light weight panels in the high-speed railway technology and high-speed ship like as cruise yachts. Also it has been used in the aircraft and aerospace industry as a structural panel because light weight structure is indispensible in that field of industry. Recently, the honeycomb panel is embossed in the viewpoints of high oil prices as the lightweight panel of the transport machine, however the sound insulation capacity of the honeycomb panel is poorer than those of uniform and another sandwich panels. In this paper a method to improving the sound absorption coefficient of a honeycomb panel Is studied by using the Helmholtz resonator. The sound absorption coefficients for some kinds of honeycomb cores are demonstrated by the normal incident absorption coefficient method.

• The Journal of the Acoustical Society of Korea
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• v.37 no.4
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• pp.181-187
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• 2018

In this paper, sound absorption of micro-perforated elastic plates installed in an impedance tube of a circular cross-section is discussed using an analytic method. Vibration of the plates and sound pressure fields inside the duct are expressed in terms of an infinite series of modal functions, where modal functions in the radial direction is given in terms of the Bessel functions. Under the plane wave assumption, a low frequency approximation is derived by including the first few plate modes, and the sound absorption coefficient is given in terms of an equivalent impedance of a single surface. The sound absorption coefficient using the proposed formula is in excellent agreement with the result by the FEM (Finite Element Method), and shows dips and peaks at the natural frequencies of the plate. When the perforation ratio is very small, the sound absorption coefficient is dominated by the vibration effect. However, when the perforation ratio reaches a certain value, the sound absorption is mainly governed by the rigid MPP (Micro-Perforated Plate), while the vibration effect becomes very small.

• Journal of Korean Association for Spatial Structures
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• v.8 no.3
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• pp.53-63
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• 2008

In this study, the reverberation characteristics of coupled spaces were investigated using a scale model. Two rooms were connected through an acoustically transparent opening known as an aperture. The acoustic characteristics of the coupled room by varying three parameters, the aperture opening size, the absorption ratio between the two rooms and the locations of the secondary room, were measured and analysed. The results indicated that a reverberant secondary room, produced large variations of the acoustics in the main room and an absorptive secondary room was effective to provide systematic control of the acoustics in the main room. The reverberant secondary room should be located at the rear of the stage and the aperture opening ratio over 6.25% produced large variations of the acoustics in the main room. However, the aperture opening ratio over 25% had no effect on variations of the acoustics in the main room. The absorptive secondary room should be located at the rear of the audience areas and the aperture opening ratio over 3.13% produced large variations of the acoustics in the main room.

• Journal of Advanced Marine Engineering and Technology
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• v.41 no.1
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• pp.50-55
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• 2017

Foamed aluminum is an eco-friendly material that is reusable and safe against fire. These superior characteristics have many advantages in the field of building and construction and in cruise ships as sound absorbers. So far, the research on foamed aluminum has been focused on the sound absorption performance using the foaming ratio. Foamed aluminum, when compared with the existing sound absorbers such as glass wool or rock wool, has a better structural performance, and it can be installed on walls in many different ways. This study conducted experiments on the sound absorption characteristics considering the various applications of foamed aluminum. The effects of painting surfaces with the finishing material were compared to that of the normal surface, and the effects of vertical installation and hanging from the ceiling was compared with the effects of installing on the floor.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1994.04a
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• pp.201-205
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• 1994

본 실험에서는 한개의 마이크로폰만을 이용하여 소음기내에 삽입된 재료의 흡음율을 임피던스관에서 전달함수기법으로 측정하고 측정값의 정확성을 확인하기 위하여 정재파법으로 측정한 결과와 비교하여 보았다. 또한 이 측정법을 단순팽창형 소음기에 적용하여 소음기의 투과손실을 측정한 후, 이론과 비교하여 측정의 정확성을 검토하였고 소음기내에서의 흡음재의 위치에 따른 투과손실의 변화에 대해서도 이론과 비교 검토하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.340-343
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• 2000

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.645-648
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• 2005

The grounds of multipurpose practical use degree are built much holding world cup 2002 but material that is used in this building most external membrane ceiling is accomplishing PTEE A master and servant. Therefore, this research analyzed assessment about sound absorption special quality that measure ventilation quantitys of 10 act material and analyze correlation with Air Permeability and the sound absorption rate, and follow in change of layer of air of inside facts material. Result is as following. When Air Permeability good dimension is 5$\sim$15 cc/cm$^2$/sec and acoustic absorptivity is the best as Air Permeability result that measure acoustic absorptivity of inside facts material particularly firstly, could know 8$\sim$9 cc/cm$^2$/sec love. When establish sound absorption inside facts in external membrane as result that measure acoustic absorptivity of inside (acts material secondly, could know that acoustic absorptivity is good though become about minimum back layer of air 900mm.