• 한국음향학회:학술대회논문집
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• 한국음향학회 2000년도 하계학술발표대회 논문집 제19권 1호
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• pp.287-290
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• 2000

In periodic structures where two or more materials of different density and sound speeds are arranged, there exist stop bands, in which waves cannot propagate. In this paper noise and vibration reduction by using band gap phenomena is discussed. The general theoretical background is presented and experimental results for acoustic wave attenuation in 2D cylinder arrays are described.

• 한국소음진동공학회논문집
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• 제14권2호
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• pp.87-94
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• 2004

In this paper, the experimental design of an intake system was studied using the two microphones method and the taguchi method. The transmission loss was utilized to represent the performance of noise reduction for the intake system which was estimated by measuring sound power at inlet and outlet with two microphones, respectively. Two microphones method used in this paper was followed by wave decomposition theory. The robust designing parameters of an intake system were extracted by adapting a cost function with the taguchi method, which optimized the process. Finally the effectiveness of the propose method was validated with the experimental data.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 추계학술대회 논문집
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• pp.92-95
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• 2011

The walls of modern train cars are required to have higher transmission loss since modern train have had high speed and light weight. The method based on Reverberation Chamber like KS F 2808 could be used to measure transmission loss. However, this method has difficulty in that constrained Standard of it requires extremely large facilities. Recently, the method based on Scale Reverberation Chamber is used as an alternative to Reverberation Chamber. The method of Scale Reverberation Chamber is known to be small and economical but it provides standing wave that directly influences measurement error. Therefore, this research is focus on predicting standing waves based on method of FFM and reducing measurement error by changing shape of chamber.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.114-119
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• 2003

In this paper, the experimental design of an intake system was studied using the two microphones method and the taguchi method. The transmission loss was utilized to represent the performance of noise reduction for the intake system which was estimated by measuring sound power at inlet and outlet with two microphones, respectively. Two microphones method used in this paper was followed by wave decomposition theory The robust designing parameters of an intake system were extracted by adapting a cost function with the taguchi method, which optimized the process. Finally the effectiveness of the propose method was validated with the experimental data.

• 한국소음진동공학회논문집
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• 제14권7호
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• pp.577-585
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• 2004

In this paper, reactive shearing structural intensity method is extended to damping patches placement on outer panels of outdoor unit of air-conditioner to reduce its structural borne noise. The structural intensity is calculated from the normal velocities of structures that are measured by using a laser scanning vibrometer, and $textsc{k}$-space (wave-number domain) signal processing is used to obtain the spatial derivatives in formulation of structural intensity. This method is applied to the outdoor unit of air-conditioner on shaker-exciting mode and operating mode. and then damping patches are placed over area of high reactive shearing structural intensity for reducing the radiated noise. Experimental results show the largest reduction of sound pressure level of an outdoor unit by appling small damping patches to optimal position.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 추계학술대회 논문집
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• pp.821-832
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• 2011

Recently, the noise of vehicle is the one of the key factors for customers to purchase a vehicle and the most important part which is related to the noise is the exhaust system. Thus, car makers have their own ways to assess this exhaust noise not only to decrease the level of noise but to enhance the feeling of it. Typically, to do these things in the early stage of development, the tuning code of the exhaust system has to be made by CAE tool, which is very reliable but expensive, and the prototype parts of this code would be made for the validation test. Then this process can be iterated to meet the target of the performance. In this study, a new algorithm which adapts the '3 dimensional convective sound wave theory 'and 'Doppler effect' has been developed. With this new algorithm, a brand new system for the calculation of tail pipe noise has been developed and validated by acoustic wind tunnel test. As a result of this study, various comparisons and have been carried out, for example, the comparison with other CAE tool has been performed for the validity and the improvement of the new calculation code could be achieved.

• The Journal of the Acoustical Society of Korea
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• 제25권2E호
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• pp.79-84
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• 2006

Acoustic characteristics of a sound absorbing material can be identified, if the characteristic impedance and propagation constants are known, which have generally been determined experimentally. One easy method determining these two essential parameters is to measure the one dimensional wave characteristics in the impedance tube. In th udy, the effects of backing conditions on the impedance tube measurement have been examined using several pairs of generally used end conditions. The results showed that the measured values are similar for most pairs of end conditions: however, it was observed that the measured characteristic impedance for different thickness did not agree well for some pairs. In this work, the multi termination method, using three or more known backing con ns, was suggested to reduce such random errors, which are mostly caused by the test procedure. Employing three terminations as a set, comprised of a rigid end, an end with porous material, and an end with a backing cavity, it was demonstrated that improved measured results could be obtained for an open cell PU foam varying widely with three different thicknesses.

• 한국음향학회지
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• 제28권2호
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• pp.127-134
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• 2009

본 연구에서는 다양한 두께의 유리창을 대상으로 레이저 원격 도청 가능성을 검토한다. MLS 신호음을 사용하여 유리창을 진동시키고 레이저 도플러센서로 진동음을 탐지한다. 탐지된 진동음으로부터 음성정보의 인식 수준인 음성명료도를 객관적으로 평가한다. 평가에는 변조전송함수에 근거하여 결정되는 음성전송지수를 사용한다. 또한, 외부 스피커와 유리창 교란기로 각각 교란파를 발생시켜, 배경소음과 도청방지기의 음성명료도에 대한 교란효과를 평가한다. 다양한 두께의 유리창을 대상으로 레이저 원격 도청음의 음성인식 수준과 국산 도청 방지장치의 도청방지 성능을 평가하는 데에 본 연구의 목적이 있다.

• 한국음향학회지
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• 제35권4호
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• pp.253-260
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• 2016

본 논문은 중간에 공기층을 포함한 이중 판이 임피던스 튜브 내에 고정된 경우 이중 판의 음향투과손실(Sound Transmission Loss, STL)을 해석적으로 구하는 방법을 다루었다. 평판의 진동과 튜브 내부 음장을 모드 함수의 무한급수의 합으로 전개하였다. 평면파 가정을 이용하여 처음 몇 개의 모드만 고려하여도 충분히 정확한 결과를 얻음을 보였으며 피크와 골(dip)의 발생 위치를 조사하였다. 이중 판의 피크는 각각의 단일 판의 피크와 같은 주파수에서 발생함을 보였다. 두 개의 판이 동일한 경우 STL은 단일 판과 마찬가지로 판의 고유진동수에서 제로가 된다. 공기층 간격이 작은 경우에 대한 근사식을 사용하여 STL의 골과 크기를 규명하였다.

• 한국음향학회지
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• 제39권4호
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• pp.270-278
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• 2020

본 논문은 원통형 임피던스 튜브내에 설치된 다중 미세천공판(Micro-Perforated Plate, MPP)의 음향투과를 해석적으로 구하는 방법을 다루었다. 판의 진동을 무한 급수의 합으로 전개하였는데 반경방향으로는 Bessel 함수를 포함한다. 평면파 가정하에서 저주파수 대역의 근사식을 유도하였으며 전달함수법을 이용하여 다중 MPP에 대한 음향투과율 공식을 제시하였다. 단일과 이중 MPP의 음향투과손실(Sound Transmission Loss, STL)을 본 논문에서 제안한 공식을 이용하여 계산하였으며 유한요소법(Finite Element Method, FEM)을 사용한 결과와 잘 일치 하였다. 천공율이 증가할수록 STL은 감소하는데 이는 판의 진동보다는 천공율이 더 큰 영향을 주기 때문이다. STL은 판의 공진주파수에서 골(dip)을 보이며 이중 MPP의 STL은 질량-스프링-질량 진동에 해당하는 공진주파수에서 골을 보인다. 본 연구에서 제안한 STL 예측 모델은 임의의 개수의 다중 MPP에 적용이 가능하며 각각의 판은 미세천공을 포함하거나 포함하지 않는 두 가지 경우가 모두 가능하다.