• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.4 s.121
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• pp.342-349
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• 2007

Following the 2002 World-Cup held in Korea, studies have been actively conducted on plans to utilize all-weather stadiums of fine figures, where large-scale spaces are available for various utilizations. In Japan, dome-type stadiums have been built and are utilizing across the whole nation not only for sports events but also variety of other large-scale events. PTFE(poly tetra fluoro ethylene) is one of the membrane material mainly used for the outer ceiling surface of membrane structures. However, there has not been enough research on the acoustical properties of PTFE membrane material which has been widely used in the multi-purpose stadiums. In this study, air permeability values and sound absorption coefficient of PTFE membrane materials were measured and evaluated in the gymnasium. From the results of measurements of sound absorption coefficient and air permeability of inner membrane materials, it was found that the sound absorption coefficient was good in the air permeability range of $5{\sim}15\;cc/cm^2/s$. Also the relation ship between air permeability and sound absorption coefficient was very high and the sound absorption coefficient was the highest in the range of $6{\sim}9\;cc/cm^2/s$. Secondly, an analysis on the measurements sound absorption characteristics of inner membrane material reveals that the overall sound absorption coefficient was stabilized(higher than 0.5 throughout the whole frequency bands) when the air space behind the membrane material was deeper than 600 mm. When PTFE sound absorptive membrane material was installed in the ceiling of gymnasium, it was confirmed that sound absorptive membrane material can reduce reverberation and increase speech intelligibility in the gymnasium.

• Journal of the Korean Ceramic Society
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• v.40 no.3
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• pp.273-278
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• 2003

The effects of content and particle size of sewage sludge slag on the sound absorption was investigated and the physical$.$mechanical properties of porous ceramics for sound absorbent material was studied. The physical$.$mechanical properties of specimens have depended on sintering temperature and slag content without particle size effect of slag. As water glass content increase and particle size of slag decrease at the same slag content, physical$.$mechanical properties of them have been improved. The bulk density and compressive strength of specimens with the batch composition of 77∼89 wt% of slag content and particles with 1∼3 mm, and sintered at 1,050$^{\circ}C$ for 2 h were 1.48∼1.71 and 86∼163 kgf/$\textrm{cm}^2$, respectively. The specimens with 1∼3 mm and <1 mm of particles size showed good sound absorption property at low frequency and high frequency region. With increasing thickness of specimens, sound absorption properties at low frequency region were increased.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.449-452
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• 2005

Sound absorption coefficient is affected by void in sound absorbing materials, therefore it is important to analyze properties of void pore. Also, it can be used to estimate performance of foamed concrete when it is applied to absorb sound. The purpose of this study is to analyze the sound absorption coefficient and void characteristic of foamed concrete using bottom ash. As a result of experiment, it was determined that an increase in sound absorption coefficient is achieved by increasing added amount of foam.

• Journal of the Korean Wood Science and Technology
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• v.43 no.2
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• pp.206-213
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• 2015

This study was carried out to use carbonized medium density fiberboard (MDF) for the replacement of sound absorbing material. Carbonization treatment was performed to improve sound absorption property for MDF at carbonizing temperatures of $500^{\circ}C$, $700^{\circ}C$, $900^{\circ}C$ and $1100^{\circ}C$. As the carbonization temperature increased, the results of the observation by scanning electron microscope (SEM) demonstrated that the fibers exhibited a more compressed morphology within the surface section of the MDF than those within the middle section of MDF. As the carbonizing temperature increased, the cavity increased. The sound absorption coefficient increased between the temperatures of $500^{\circ}C$ and $900^{\circ}C$, but decreased at a temperature of $1100^{\circ}C$. The sound absorption properties of the carbonized MDF and the non-carbonized MDF were compared. The maximum sound absorption coefficient of the carbonized MDF was 12.38%. This was almost double of the value of the non-carbonized MDF.

• Journal of Korea Foundry Society
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• v.31 no.3
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• pp.145-151
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• 2011

Metallic foam has been known as a functional material which can be used for absorption properties of energy and sound. The unique characteristics of Al foam of mechanical, acoustic, thermal properties depend on density, cell size distribution and cell size, and these characteristics expected to apply industry field. Al-Zn-Mg-Cu alloy foams was fabricated by following process; firstly melting the Al alloy, thickening process of addition of Ca granule to increased of viscosity, foaming process of addition of titanium hydride powder to make the pores, holding in the furnace to form of cooling down to the room temperature. Metal foams with various porosity level were manufactured by change the foaming temperature. Compressive strength of the Al alloy foams was 2 times higher at 88% porosity and 1.2 times higher at 92% porosity than pure Al foams. It's sound and vibration absorption coefficient were higher than pure Al foams and with increasing porosity.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.1222-1227
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• 2002

Noise barrier is used to reduce traffic noise. The effect of a noise barrier depends not only on the materials, but also on the physical properties such as density, height and degree of absorption, etc. Typical absorptive noise barrier is used sound absorbing material, such as glass wool and mineral wool. The goal of this study is to develope excellent absorptive noise barrier using a polyester. Laboratory measurements were peformed with various thicknesses, density and layer of absorber in a reverberation room.

• KIEAE Journal
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• v.6 no.1
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• pp.11-16
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• 2006

This paper deals with the experimental for manufacturing the lightweight buildng materials with portland cement, fly ash, slag, lime, gypsum, and aluminum powder system. Aluminum powder was added an aerating agent. Specific gravity range of lightweight concrete specimens were 0.6~0.9g/cm3. These specimens properties studied by means of specific gravity, compressive strength, absorption coefficient, transmission loss and scanning electron microscopy. Cellular concrete with maximum compressive strength was 41kgf/cm2 by obtained Al=0.05wt.%. Moreover, the aeration lightweight concrete showed excellent sound absorption properties.

• Polymer(Korea)
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• v.34 no.5
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• pp.410-414
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• 2010

Two different types of polymer-modified mortars(PMM) were prepared with recycled PET and fly-ash. One is rigid PMM and the other is flexible PMM which are based on the composition of recycled PET. Their mechanical properties including friction coefficient measurement and damping characteristics such as sound absorption were investigated and compared with the commercial PMM such as epoxy PMM and PET PMM. The result from mechanical properties indicated that the rigid PMM could be competitive with the commercial PET PMM. The measurement of sound absorption coefficient showed that both rigid PMM and flexible PMM had much better damping capacity than commercial PMM. However, the friction coefficient of rigid PMM revealed that it would be suitable for the use as floor material.

• The Journal of the Acoustical Society of Korea
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• v.40 no.3
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• pp.254-260
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• 2021

When measuring the sound absorption coefficient of a specimen, a reverberation room which is costly or an impedance tube which has limitations in measuring low frequencies have been engaged. In this paper, a new measurement method of acoustic impedance or sound absorption coefficient has been suggested, which does not need microphones and only uses electrical impedance measurement data and derived Thiele/Small parameters of a speaker. The theory of this method has been described using equivalent circuit of the loudspeaker and acoustic properties of a test specimen are measured to demonstrate the validity of this method. It was confirmed that this method can easily measure the sound absorption coefficient in the low frequency band, which was previously difficult to trust. The advantages, limitations, and applicability of this method are discussed.

• Ocean and Polar Research
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• v.29 no.2
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• pp.113-121
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• 2007

The sound wave in the sea propagates under the effect of water depth, sound speed structure, sea surface roughness, bottom roughness, and acoustic properties of bottom sediment. In shallow water, the bottom sediments are distributed very variously with place and the sound speed structure varying with time and space. In order to investigate the seasonal propagation characteristics of low-frequency sound wave in the Yellow Sea, propagation experiments were conducted along a track in the middle part of the Yellow Sea in spring, summer, and autumn. In this paper we consider seasonal variations of the sound speed profile and propagation loss based on the measurement results. Also we quantitatively investigate variation of bottom loss by dividing the propagation loss into three components: spreading loss, absorption loss, and bottom loss. As a result, the propagation losses measured in summer were larger than the losses in spring and autumn, and the propagation losses measured in autumn were smaller than the losses in spring. The spreading loss and the absorption loss did not show seasonal variations, but the bottom loss showed seasonal variations. So it was thought that the seasonal variation of the propagation loss was due to the seasonal change of the bottom loss and the seasonal variation of the bottom loss was due to the change of the sound speed profile by season.