• 소음진동
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• 제4권2호
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• pp.187-198
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• 1994

This study is to describe the effects of the duct termination conditions conditions upon the active noise attenuation system. The adaptive filtering algorithm using FIR filter is implemented for duct noise attenuation. To avoid the instability caused by the acoustic feedback, two methods are considered. One is to use a compensating FIR filter. The other is to utilize uni-directional detecting microphone and uni-directional control speaker. Experimental results show that the reflections of sound from duct terminations greatly reduce the performance of ANC system. The directionality of detecting microphone and control speaker is a major factor to decide ANC performance. When there are some reflections from both duct terminations, the noise attenuation using finite FIR filter is not enough to model the duct plant. Especially, the reflection from the upstream termination reduces the noise attenuation in the frequencies related to the distance between control speaker and upstream termination. The performance of the noise attenuation is found to be largely enhanced by using uni-directional coupler, both on detecting microphone and control speaker, even if the duct system has an arbitrary termination conditions.

• 한국안전학회지
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• 제10권2호
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• pp.32-38
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• 1995

The silencers are used to attenuate noise generated by the exhaust fan for industrial processes. The types of silencers applied in this study are absorptive duct silencer, expansion chamber, absorptive chamber and resonator. This study was carried out to verify the attenuation by the various silencers and elements. As a result, the difference of attenuation between the calculation and the measurement was about 1-7㏈. The attenuation by absorptive duct silencer and absorptive chamber was negligible at frequencies below 250Hz. The expansion chamber should be used for low frequency applications where the absorptive duct silencer was Ineffective. The attenuation by resonator may be realised when the ratio of frequency to resonant frequency approaches 1.

• 한국해양공학회지
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• 제26권3호
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• pp.13-19
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• 2012

Recently, as the importance of the interior noise in a ship cabin has risen, ship builders have becomeconcerned about the use of noise reduction panels to reduce cabin noise. The results of previous researches have been based on analytical and experimental methods using simple sandwich panels. However, panel structures are becoming more complex to improve the transmission loss. Thus, researches that analyze the transmission loss of a panel are reaching the limit of study. This paper reports on research that was performed to determine the sound transmission characteristics of multi-complex panels applicable to high value-added vessels. It presents comparisons between analytical methods and experimental results by using a mini-reverberant chamber with components of sound attenuation panels, including the core and surface materials. The sound transmission loss of multi-complex panels are also analyzed in terms of the influences of the inside perforate plates and air gap thickness on the attenuation. Finally, the multi-complex panel with the highest noise attenuation is proposed based on the analysis results and experimental results in mini-reverberant chamber, which wereverified using a real-size reverberant chamber.

• 비파괴검사학회지
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• 제35권2호
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• pp.103-111
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• 2015

본 연구에서는 골절 위험도가 높은 대퇴골의 두꺼운 피질골판이 해면질골의 초음파 특성에 미치는 영향을 조사하였다. 이를 위해 소의 대퇴골을 이용하여 12개의 해면질골을 제작하였으며, 피질골과 유사한 밀도 및 음속을 갖는 아크릴을 이용하여 피질골판을 모사하는 1.25, 1.80, 및 2.75 mm의 두께를 갖는 아크릴판을 제작하였다. 해면질골 양면에 부착된 아크릴판의 두께가 증가하더라도 음속과 해면질골의 겉보기 골밀도 사이에 Pearson 상관계수는 0.80-0.86의 값을 가지며, 높은 상관관계가 존재하는 것으로 나타났다. 또한 0.5 MHz에서 측정된 감쇠계수와 해면질골의 겉보기 골밀도 사이에 Pearson 상관계수는 0.84-0.91의 값을 가지며, 높은 상관관계가 존재하는 것으로 나타났다. 이와 같은 결과로부터 종골에 비해 상대적으로 더 두꺼운 피질골판을 갖는 대퇴골에서 측정된 음속 및 특정 주파수에서의 감쇠계수는 대퇴골의 골밀도를 예측하기 위한 지표로서 이용될 수 있음을 알 수 있다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.379-382
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• 2005

Recently, we founded acoustic research laboratory consist of five reverberation rooms on the basis of ISO regulations. Four kinds of experiment are possible in our laboratory such as sound transmission loss of wall, sound attenuation of suspended ceiling, absorption coefficient, reduction of transmitted impact sound by floor coverings. We are going to provide our customers with officially authorized acoustics data.

• KIEAE Journal
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• 제7권2호
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• pp.3-8
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• 2007

Recently, the structural system of public residential buildings has been changed from the reinforced concrete (RC) wall system to the (PC) wall and moment resisting systems. Thus, it is important to develop the suitable wall system in accordance with the trend of the modern structural system. This paper presents the basic study on the suitable boundary wall in high-rise buildings. The research also demonstrates the evaluation results on sound characteristics in the aspect of sound insulation. The evaluation of sound insulation capability for the commercialized wall structure was conducted based on literature survey while the measurement of sound insulation capability for the light-weght EPP concrete was performed in according to KS F2808 in laboratory. The main objective of this research is to propose the most suitable dry wall system as a sound insulation structure through the comparison and analysis of frequency characteristics and weight-acoustic attenuation.

• 한국음향학회지
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• 제19권1호
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• pp.40-47
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• 2000

감쇠가 심하고 분산적인 폴리우레탄 재료의 음향특성을 평가하기 위하여 초음파 투과법을 이용하였다. 투과법에 있어서, 작은 크기의 시편에 적용할 수 있도록 Sachse의 방법을 이용하여 음속과 음향감쇠계수를 측정하였다. 기준 신호를 이용하여 음향특성을 측정하였을 때 정확한 결과를 얻기 어려웠다. 반면, 두께가 서로 다른 두 우레탄 시편을 가지고 음향특성을 측정하였을 때 보다 정확한 결과를 얻을 수 있었다. 저주파 대역에서의 음향특성을 파악하기 위하여 Kramers-Kronig 관계를 적용하였다. 이를 통해 저주파 영역까지 확대된 주파수에 따른 음속관계식을 구하였고, 음속과 음향감쇠계수의 상관관계를 연구하였다.

• 한국해양공학회지
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• 제26권2호
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• pp.14-19
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• 2012

There are insufficient data to consider the effect zone for the marine life of coastal fisheries, because no standard has been defined for the sound level of marine life. In this study, equations for distance attenuation were used to determine the effect zone for oceanic noises. A reference noise level was divided into 4 parts to consider the characteristics of the fishes, and the effect zone of each reference noise level was determined. To increase the reliability of the effect scope, approximately 100 repetitions of blasting work split into several parts by the boring depth, the sound level of the source caused by an increase in weight, and the effect zone were calculated using the prediction equation. According to the prediction, the maximum distance of the effect zone was 4.92 km.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1987년도 전기.전자공학 학술대회 논문집(II)
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• pp.1243-1246
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• 1987

To characterize the biological tissues, the new methods to measure the frequency dependent attenuation are presented in this paper. In general, ultrasonic phase information was assumed by linear function of the frequency. But, the minimum phase function which characterizes the frequency dispersion of tissue was derived in [l]. It is very significant to measure the attenuation by using the minimum phase function to characterize the frequency dispersion of tissue. Therefore, a more efficient method measuring the frequency dependent attenuation are proposed by using the estimated sound velocity and polarity of reflected signal. To verify the algorithms, pulse reflection experiments are performed.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1998년도 학술발표대회 논문집 제17권 2호
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• pp.133-136
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• 1998

The aim of the work described in this paper is to develop a complex underground acoustic system which detects and locates the origin of an underground hammering sound using an array of six hydrophones located about 100m underground. Two different methods for the sound localization will be presented, a time-delay method and a power-attenuation method. In the time-delay method, the cross correlation of the signals received from the array of sensor sis used to calculate the time delays between those signals. In the power-attenuation method, the powers of the received signals provide a measure f the distances of the source from the sensors.