• Title/Summary/Keyword: absorption coefficient

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The study on the estimation of diffuse field absorption coefficient by using normal incidence impedance (수직입사 임피던스를 이용한 난입사 흡음율 예측 연구)

  • 유승국;김영찬;김두훈
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 1998.04a
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    • pp.643-649
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    • 1998
  • This paper is to compare the absorption coefficient with normal incidence waves and it with diffuse incidence waves of glass wool which the most used absorption material and multi layer fiber. The absorption coefficient with normal incidence waves is calculated by surface impedance that measured by using an acoustic tube. Based on this data, the absorption. coefficient with diffuse incidence waves is predicted and is compared with measured the absorption coefficient in reverberation room.

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Sound Absorption Characteristics of Permeable Membrane (통기성을 갖는 막재료의 흡음특성)

  • Jeong, Jeong-Ho;Kim, Jung-Joong;Kim, Ku-Je
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2009.10a
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    • pp.270-275
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    • 2009
  • Sound absorption characteristics of membrane system which are used in stadiums and arenas were investigated. Theoretical studies on acoustic properties of single and double leaf permeable membrane conducted. Also, experimental studies on sound absorption characteristics of combined membrane system that is composed of outer and inner membrane material were conducted. In this study, sound absorption characteristics of each membrane were investigated by experiments in reverberation chamber. 4 types of permeable membranes and a non-permeable membrane were used for experiments. Air space behind membrane material and tension on the membrane was varied. Sound absorption performance of permeable membrane materials was confirmed. As increasing air space behind the membrane material, sound absorption coefficient was increased. In a resonance absorption frequency band sound absorption coefficient varied more dramatically. Sound absorption characteristics were flat in mid and high frequency range and sound absorption coefficient was from 0,3 to 0,5. Also sound absorption coefficient was increased by the increment of surface density and air permeability of membrane. However, over the certain value of air permeability, sound absorption coefficient was decreased. These results can be used as design factors and method for the room acoustic design of dome-stadiums and large free-form buildings.

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A Study on the Characteristic of Sound Absorption of Flyash Blocks (Flyash를 이용한 블록의 흡음특성에 관한 연구)

  • 변홍식;이태관
    • Journal of Environmental Science International
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    • v.11 no.3
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    • pp.235-240
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    • 2002
  • The blocks using flyash were prepared in this study. The characteristic of sound absorption of flyash block was investigated. It was revealed that the chemical additives and flyash played an important role to determine the characteristic of sound absorption. Chemical additive affects the capability of sound absorption while flyash affects the characteristic of sound absorption, i.e. high value of the sound absorption coefficient at the specific frequencies(1KHz and 2KHz). The flyash block showed higher sound absorption coefficient than that of the commercial concrete block having carpet on the surface. It was also shown that the sound absorption coefficient increases with increase of the content of flyash in the block. However, it was found that the 70wt% of flyash in the flyash block was the optimum content to obtain the highest sound absorption coefficient.

A Study on the Sound Absorption Coefficient by Varying Sample Size (시편의 크기에 따른 흡음계수 변화 연구)

  • 정성수;이우섭;조문재;서상준
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.11 no.5
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    • pp.83-88
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    • 2001
  • The sound absorption coefficient of glass wool (bulk density of 48 kg/m:1 and 32 kg/m7) was measured by reverberation room method as varying their cross-sectional area. The results show that the absorption is larger for smaller samples because of edge effect. The absorption coefficient with two different kinds of sources. 1/.7-octave band and while noise, gives similar values.

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Measurements of absorption coefficients of open-type ceilings using 1:25 scale model reverberation chamber (축척모형을 활용한 개방형 천장의 흡음률 측정)

  • Lee, Hye-Mi;Kim, Yong-Hee;Jeon, Jin-Yong
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2007.11a
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    • pp.683-686
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    • 2007
  • This paper investigates acoustical characteristics of open-type ceilings using 1:25 scale model. The field survey in the existing 15 halls was carried out to figure out the ceiling structure. The components of the open-type ceiling were mainly steel truss structures, duct, catwalk and finishing surfaces. In order to investigate the absorption characteristics of the equipped ceiling, the absorption coefficient measurements were made using 1:25 reverberation chamber based on ISO 354. Results showed that the absorption coefficient of the empty ceiling structure (6m-height) with 50%-perforated covering plate was 0.2-0.3 at above 500 Hz. When steel structure was added inside the empty ceiling, absorption coefficient increased by 0.16 at 250-1kHz. Adding catwalk did not increase the absorption, but adding duct increased the absorption at 1-2kHz. NRC of the equipped ceiling was 0.39, and the absorption characteristics were mainly found at high frequencies. In addition, the opening size of the covering plate did not change the absorption coefficient of the equipped ceiling meaningfully.

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Measurements of scattering and absorption coefficients of diffusers with variation of surface area (확산체의 표면적 변화에 따른 흡음 및 확산계수 측정)

  • Kumar P., Senthil;Kim, Yong-Hee;Jeon, Jin-Yong
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2007.11a
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    • pp.983-986
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    • 2007
  • The absorption power of a surface depends on the surface irregularity which has been known as an important factor in determining scattering coefficient. This study investigates the effect of increase in surface area on the absorption and scattering coefficients of a diffuse surface. The surface irregularity or surface pattern can be compared to the wavelengths and the random-incidence scattering coefficient of surface is measured by ISO 17497-1. The scattering coefficients of increasing the surface area in linear pattern of v-cut groove on rubber plate were measured in 1:10 scale model reverberation chamber. It is found that the scattering and absorption coefficients increase with increasing surface area. At 60% of increased surface area the spacing between the hemisphere diffuser and the v-cut groove acts similar with results of absorption coefficient. The results show that absorption coefficient depends on surface area and the spacing where as scattering coefficient depends on surface area and texture.

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A Study on the Shock Absorption Performance of the Safety Helmet using Coefficient of Restitution (반발계수를 이용한 안전모의 충격 흡수 성능에 관한 연구)

  • Shin, Woon-Chul
    • Journal of the Korean Society of Safety
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    • v.27 no.5
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    • pp.30-34
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    • 2012
  • A safety helmet is a personal protective equipment to protect the head from falling and flying objects. A safety helmet has the maximum delivered impact force as shock absorption performance, the lower delivered impact force the better performance, which was not a controlled variety during manufacturing safety helmet. Accordingly there were some difficulties in establishing the standard for improved performance as there was not a clear controllable impact force for improved performance. In this study the shock absorption performance was intended to be found as coefficient of restitution related to impulse. As a research method, a coefficient of restitution during the absorption of shock was calculated using the impulse transferred to pharynx utilizing the safety helmet shock absorption performance testing device based on the theory of momentum and impulse. The estimated impulsive force curve was derived assuming that shock was not absorbed using the measured data. The sample was selected as tested goods of ABS material for safety certification available mainly in the market. As a result of study, the maximum delivered impact force of safety helmet made by a domestic safety certified a company was 735 N, and its coefficient of restitution proved to be 0.64. The smaller coefficient of restitution is, the lower maximum delivered impact force and the higher shock absorption performance. The coefficient of restitution can be used as a performance index of safety helmet.

A Study on the Noise Absorption of Textiles for Interiors (실내장식용 섬유소재의 흡음성에 관한 연구)

  • Choi, In-Ryu;Bang, Hey-Kyong
    • The Research Journal of the Costume Culture
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    • v.20 no.4
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    • pp.475-484
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    • 2012
  • The purpose of this study is to help to prevent daily noises by measuring the noise absorption coefficient of the non-woven fabrics and wallpapers which are commonly used in lining and noise absorption coefficient of lining curtain. Seven types of fiber materials for the interior decoration, one non-woven fabric for the wallpaper linings, and two types of textiles for curtain linings are used as the experimental materials in this study. The noise absorption coefficient of the noise absorbents were measured by using impedance tube. And the thermal transmittance were measured by using thermal transmittance tester. The results of this study are as follows; Observing the noise absorption efficiency of each experimental materials, the combination of fiber materials and linings, the noise absorption efficiency of cotton, polyester and silk were similar and for the experimental materials of flax, rayon, acrylic and nylon were resulted the similar noise absorption efficiency. The result of combination of fiber material and black fabric was highest among the combined linings. For the combination of fiber material and non-woven fabric, double layers of non-woven fabric resulted slightly higher noise absorption coefficient result than single layer of non-woven fabric. The thermal transmittance and the sound absorbents of experimental materials were affected by the thickness, density and layer of air of the experimental materials.

Sound Absorption Performance of Noise Barrier According to Single Number Rating Methods (단일수치 평가방법에 따른 방음벽의 흡음성능 고찰)

  • Kim, Yonghee;Lee, Sungchan
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.27 no.2
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    • pp.243-250
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    • 2017
  • In this study, single number rating methods of sound absorption coefficients are discussed. After that the sound absorption performance of noise barriers which are classified by Korea Standard are analyzed according to several standards. The existing rating methods such as NRC (noise reduction coefficient), SAA (sound absorption average) or ${\alpha}_w$ (weighted sound absorption coefficient) from ASTM C423, KS F 3505 and ISO 11654 are introduced. The sound absorption performance of noise barrier is evaluated to compare NRC and ${\alpha}_w$ value. When the value is over 0.6 there are large variance between NRC and ${\alpha}_w$ value. As results, it is needed to unify single number rating methods of sound absorption coefficients for Korean standards on sound absorbing materials.

Sound Absorption and Thermal Insulation Characteristics of Membrane Used for Sound Field Control (음장제어용 막재료의 음향 및 단열특성)

  • Jeong, Jeong-Ho;Kim, Jeong-Uk;Jeong, Jae-Gun;Cho, Byung-Wook
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.22 no.2
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    • pp.103-114
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    • 2012
  • Nowadays membrane material is widely used for large indoor spaces and long spaces such as traditional market. Thermal insulation and sound field control performance is considered as a main properties for design of such buildings. In this paper sound absorption and thermal insulation properties of membrane material was investigated. Firstly, normal incidence sound absorption coefficient of 10 kinds of glass wool textiles showed that sound absorption coefficient was increased in proportion of thickness and surface density of textile. Sound absorption coefficient of 4 kinds of sound absorptive inner membrane with outer membrane was tested in the reverberation chamber. Sound absorption coefficient of mid frequency range was about 0.4 ~ 0.6. Also, sound absorption coefficient was changed by the air space behind the membrane material. Secondly, sound field control performance was investigated using mock-up space. By the installation of sound absorption membrane material, reverberation time was decreased and speech intelligibility was increased. Finally, thermal resistance and room temperature in two kinds of mock-up rooms were tested, simultaneously. Results of thermal properties showed thermal insulation properties ware increased by adding inner membrane material underneath the outer membrane.