• 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.

• International Journal of Air-Conditioning and Refrigeration
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• v.12 no.2
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• pp.87-96
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• 2004

Acoustic performances of the steel-wire fabrics manufactured from the crushed tires were experimentally investigated for various thicknesses and bulk densities. The well- known two-cavity method was used to measure the characteristic impedances, the propagation constants, and the absorption coefficients. The normal absorption coefficients measured by the two-cavity method agreed well with those measured by the two-microphone impedance tube method. The experimental results showed that the magnitude and frequency range of the absorption coefficient were controllable by changing the thickness and the bulk density of the steel-wire fabrics. Therefore, the steel-wire fabrics from the crushed tires can be successfully used as a good sound absorbing material.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.05a
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• pp.334-335
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• 2010

• 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.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.885-891
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• 2003

Effects of each acoustic property on absorption characteristics of polyester fiber materials has been studied in this paper. It would be impossible for us to measure effects of each acoustic property by experimental method since we cannot make sound-absorbing materials in which only one of the properties is changed. We have adopted a numerical prediction method to carry out parameter studies for each acoustic property. And to get a general behavior of acoustic performance of the materials, the numerical simulation has been repeated to several cases of different bulk density. Finally we have obtained frequency-dependent control factors in the absorption performance which gives us design capability of acoustic absorbing materials.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.4 s.181
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• pp.60-66
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• 2006

For the purpose of finding out the sound field characteristics in a rectangular cavity, analytical and experimental studies are performed with white noise input. Two-microphone impedance tube method is used to measure the impedances of foamed aluminum. Foamed aluminum is well known metallic porous material which has excellent properties of light weight and high absorbing performance. And predicted impedances of foamed aluminum are compared with measured impedances. The predicted acoustical parameters are applied to the theoretical analysis to predict sound pressure field in the cavity. The measured sound absorption effects are compared with the predicted values for both cases with and without foamed aluminum lining in the cavity of the rectangular enclosure.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.7
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• pp.562-568
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• 2014

This study aimed to identify changes in the physical properties of artificial mineral-fiber materials used as building insulation that had been installed in the outer walls of buildings for a long time. To achieve this goal, glass fiber and rock wool were collected from outer walls in actual buildings and their acoustic and thermal performances were measured. These were compared with measurements from similar products manufactured recently. The results showed that old, used samples had a lower sound absorption coefficient compared to recently manufactured materials. The old samples also displayed increased compressibility compared to new materials. For example, the compressibility difference for glass wool was 7.32 mm. Old samples had a dynamic stiffness $1.28MN/m^3$ higher than new material samples. The thermal conductivity of both old and new samples increased within creasing temperature. They showed similar results at temperatures between 0 and $20^{\circ}C$.

• 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.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.27 no.2
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• pp.139-147
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• 2017

Acoustic performance of splitter silencers was investigated by using 3-dimensional commercial software and experiments. Flow resistivity of sound absorbing material was indirectly estimated by using an impedance tube setup and a curve fitting method. In addition the acoustic impedance of perforated plate was determined by an empirical formulation. Such properties have been used as input parameters in the commercial software. The prediction for a splitter silencer with 1000 mm length was compared with the experimental result. The numerical method is then applied to identify the effects of number of splitters, length of splitters, absorptive material density, and porosity of a perforated plate on the performance of the splitter silencers. As the number and length of splitter increases, the acoustic performance significantly increases. Although the increase of density of absorptive material also increase the acoustic performance, a change in the density over a certain level hardly affect it. The increase of porosity will enhance the performance especially at higher frequencies.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.163-167
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• 2009

In this study, the acoustic properties of ceramic 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. 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.