• 한국소음진동공학회논문집
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• 제11권7호
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• pp.253-260
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• 2001

A Study of interior noise reduction in the magelv train is presented. Tarin speed of interest is low such that aero-dynamic noise is negligible and power supply system is a dominant noise source. Based on the measurements of interior noise and acceleration levels during running and zero speed conditions, dominant noise sources are identified. After spectra characteristics of noise sources are investigated several noise reducing methods are studied such as STL increasement of floor panels. sealing. and absorption treatment It is found that the most important noise sources are VVVF inverter and SLM in running condition, whereas air conditioner and DC/DC converter are dominant in zero speed. Sine the major noise sources are under the floor complete sealing and high STL of the floor panel are shown to be the most crucial factors in noise reduction After sound absorbing material, which is polyurethan foam of 50 mm thickness, is thickness, is attached to the downward side of the floor in addition to sealing treatment, the interior noise is reduced by 3~4 dB.

• 한국소음진동공학회논문집
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• 제27권2호
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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.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.42-45
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• 2008

다목적 공간 및 공연장은 공연 또는 강연을 위한 공간뿐만 아니라 상점, 식당 및 체육 공간 등 다양한 용도의 공간이 인접되고 있다. 다양한 공간이 인접할 경우 기존의 다목적 공연장에서는 발생하지 않았던 다양한 소음 진동 문제들이 발생한다. 본 연구는 강연 및 공연을 위한 다목적 공간 상부에 식당 및 체육 시설로 활용되는 공간이 배치되어 바닥충격음 문제가 발생할 가능성이 있었다. 바닥충격음의 강당으로의 전달을 차단하기 위하여 기본 구조체에 대한 바닥충격음 차단성능을 측정하여 적절한 저감 대책을 수립하였다. 저감대책으로는 상층부 철골 슬래브와 강당의 철골 구조의 구조적 분리, 유연한 마감재 적용, 슬래브로의 충격진동 차단을 위한 제진재 적용, 이중천장 구조 및 천장내부 흡음구조 형성 등의 종합적인 대책을 수립하였다. 이를 통해 경량충격음 및 중량충격음을 효율적으로 차단하였다. 또한 강당 공간은 강연 및 집회의 공간으로 활용될 수 있도록 하기 위하여 적절한 잔향시간 및 음성 명료도 확보가 필요하다. 플러터 에코, 과도한 잔향시간, 음의 사각지대 등을 최소화하기 위하여 측벽 형태 개선, 천장 반사판 형태를 개선하였다. 또한 측벽에서 진동 등의 영향으로 발생되는 떨림현상을 억제하기 위하여 측벽 내부를 흡음재로 충전하는 등의 대책을 수립하여 적용하였다.

• 소음진동
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• 제10권2호
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• pp.240-246
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• 2000

One of the widely accepted methods for evaluating the interior sound quality of automobiles is Articulation Index(AI). The AI actually measures the articulation level of the sound in the vehicle cabin as passengers talk to one another. In this study, the effect of two different absorption materials inside the cabin on AI has been investigated by ray-tracing method : one is firewall, the other is celling. It turns out that the back seat location is found to be strongly dependent on the type of absorption materials treated at the celling, since the sound absorbing area is different due to the location and the firewall is situated in the "Reverberation Radius". The proposed methdo could be used to improve the sound quality of automobiles at the design stge.sign stge.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.762-765
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• 2005

The absorption materials have been used to enhance the performance of a noise barrier and improve the room acoustics. In this study, 6 products of absorptive materials generally used in Korea were chosen, and their absorption performance were tested in various conditions, that is, it was measured while changing thickness, density and air gap in their back, and measured with or without facing on their face. Finally, the absorption coefficients were compared by reverberation and impedance tube method.

• 소음진동
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• 제4권3호
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• pp.295-305
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• 1994

The reflection coefficient of a material at oblique incidence is measured in a free field. The sound pressure distributions are measured at discrete points on two measurement lines and then decomposed into plane wave components by using spatial Fourier transform. The inciedent and reflected plane wave components are obtained from a set of "decomposition equations" of which uses the plane wave propagation theory. Numerical simulations and experiments have been performed to see the effect of finite size of measurement area. To reduce this effect, a window fuction has been performed to see the effects of finite size of mesurement area. To reduce this effect, a window function has been proposed and its effect on the measurement of sound absorbing material property has been studied as well. The reflection coefficient obtained by this method is compared with those obtained from other methods; 2-microphone method in a duct and an expirical equation of which determines the characteristic impedance .rho.c and propagation constant k of a material from flow resistance information.formation.

• 한국소음진동공학회논문집
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• 제13권3호
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• pp.180-185
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• 2003

The equivalent electroacoustic circuit approach has been conventionally used for the analysis of the multiple layer perforated plate system. However, it is found that an analogy error has been involved in the equivalent electroacoustic approach proposed by previous researchers for the element of straight pipe. Although the pipe between the perforated layers is a distributed element in the analogy, it has been treated as a parallel element by previous investigators. The analogy error is demonstrated by comparing the calculated absorption coefficients based on the parallel circuit and the distributed circuit, respectively, with the measured values by the two-microphone impedance tube method.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.201-204
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• 2007

다양한 공연장 및 대공간에서의 실내음향 제어를 위해서는 실내마감재료의 흡음 및 확산성능을 제어할 수 있는 재료가 필요하다. 본 연구에서는 이를 위해 알루미늄 새시를 이용한 흡음구조를 개발하였으며, 흡음특성을 조사하기 위하여 수직입사 흡음계수와 잔향실법 흡음계수를 측정하였다. 수직입사 흡음계수 측정결과 알루미늄 다목적 흡음재의 타공구조와 인서트에 의해 형성되는 공간이 공명형 흡음기의 역할을 하여 중.저주파수 대역의 흡음계수가 증가되는 것으로 나타났다. 잔향실법 흡음계수 측정결과 알루미늄 새시를 이용한 흡음구조의 형성에 따라 공명주파수 대역보다 낮은 중저주파수 대역의 흡음계수가 증가되는 것으로 나타났다. 공기층 증가에 따라 공명주파수 이상 대역에서의 흡음률은 증가되고 주파수 대역별 흡음계수 편차도 감소되는 것으로 나타났으며, 고주파수 대역의 흡음률 향상을 위한 방안이 필요한 것으로 나타났다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1994년도 춘계학술대회논문집; 영남대학교, 20 May 1994
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• pp.206-211
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• 1994

본 연구에서는 임의의 복소 음압 분포를 무한 평면에서 공간상의 Fourier 변환을 하여서 평면파 요소들의 중첩으로 해석하는 방법을 살펴보고 제한된 측정 조건에서 유발되는 문제들을 음원의 주파수에 대해서 모의 실험을 통하여 고찰해보았다. 실험으로는 단단한 시편(hard panel)과 스폰지(sponge)에 대해서 공간상의 fourier 변환을 통해 반사 계수를 얻고 수직입사에 대해 2-마이크로폰 방법으로 구한 반사계수와 비교하였다. 특히 다공성 물질인 스폰지에 대해서는 유동 저항을 측정하여 실험식으로부터 구한 반사 계수와의 비교를 하였으며 공간상의 음압 분포로부터 구한 반사계수에서 창문함수의 영향을 살펴보았다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.750-750
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• 2001

Todays, according to development of traffics, there are so many tunnels around us. Tunnels are used for trains, subway trains, cars, etc. Especially for subway, all of its routes are tunnels. So the noise of the subway train cannot radiated out of the station and the noise level in the station and train cabin is so high. There are some methods to reduce this noise and one of them is using absorbing materials. But the area of the tunnel and station is very large, so it is important to determine the effective position and amount of absorbing materials before attaching them. In this study, we studied the effect of sound absorbing materials in the tunnel using boundary element method. We applied BEM for general boundary conditions. With BEM calculations, we found the effect of absorbing materials and effective positions for the subway tunnel and station.