• The Journal of the Acoustical Society of Korea
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• v.37 no.5
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• pp.363-368
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• 2018

Recently a slat type ceiling is widely used in various spaces, such as music performance spaces and concourse of airport and a general reception area of a building. However, it is hard to find a proper design guideline or material useful in designing such spaces, due to the lack of relevant researches on the effect of a slat ceiling on room acoustics. The present work investigated the effect of a slat type ceiling using a physical scale model method. A 1/20 scale model of a small shoe-box type music performance hall was built and a slat ceiling with different configurations was installed. 6 cases of different ceiling configurations were considered with the combination of 2 slat ceiling height cases and 3 distance cases between slats. The effect of a slat ceiling on the acoustics of a room was evaluated by measuring reverberance($T_{30}$), intelligibility and clarity($D_{50}$ and $C_{80}$), and loudness(G and $G_{80}$).

• The Journal of the Acoustical Society of Korea
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• v.29 no.7
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• pp.411-421
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• 2010

A time-reversal mirror (TRM) is useful in diverse areas, such as reverberation ing, target echo enhancement and underwater communication. In underwater communication, the bit error rate has been improved significantly due to the increased signal-to-noise ratio by spatio-temporal focusing. This paper deals with two issues. First, the optimal number of array elements for a given environment was investigated based on the exploitation of spatial diversity. Second, an algorithm was developed to determine the optimal location of the given number of array elements. The formulation is based on a genetic algorithm maximizing the contrast between the foci and area of interest as an objective function. In addition, the developed algorithm was applied to the matched field processing with ocean experimental data for verification. The sea-going data and simulation showed almost 3 dB improvement in the output power at the foci when the array elements were optimally distributed.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.451-454
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• 2000

실의 음향성능을 규명하기 위하여 많은 음향인자가 개발되어지고 제시되어 왔다. 음향인자 중 확산은 실의 전반적인 음향성능에 매우 유용한 것으로 여겨져 왔다. 본 연구는 장방형의 형태를 가지고 체적과 마감재료가 같은 2종류의 축척모델을 제작하여 각각의 모델에서 RT, EDT, SPL, C, IACC 등을 측정하여 확산체의 유$\cdot$무에 따른 실의 실내음향 성능을 알아보고자 한다 실험결과 실내 표면의 확산성의 차이에 따라 표면의 확산성이 좋은 공간에서 초기음장에서 음에너지가 집중되고 분산되는 것을 입증하였다. 즉 확산성이 좋은 모델에서 잔향시간(RT)은 더 짧으나 초기감쇠시간(EDT)이 더 길게 나타남으로 인하여 음에너지의 분포가 실의 확산상태에 의하여 음의 발생이후 짧은 시간내에 집중하여 전달되고 있음을 증명하였다. 또한 실의 확산상태가 좋은 공간의 명료도가 확산이 되지 않은 실에 비하여 훨씬 더 좋은 결과를 보이고 있음을 나타냈다. 이상의 결과를 종합하여 볼 때 실내 표면의 확산성이 전반적인 실내 음장의 향상에 크게 기여하고 있음을 밝혀 냈다.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.437-440
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• 2004

HMS(Hull Mounted Sonar) 운용 시 수중음속구조의 영향에 의한 음파가 경계면(해저면, 해수면)의 반사를 통해서 근거리 음영구역(short range shadow zone)을 발생시킨다(그림 1). 따라서 본 논문에서는 다양한 수중음파탐지 무기체계 가운데 특히 단상태 (monostatic) 조건일 때 HMS에 의해 발생하는 근거리 음영구역을 최소화하는 방안을 연구하였다. 즉, 2차원 수중공간 (수심-거리)에서 빔형성기법 (beamforming)을 이용한 HMS Vertical Scanning (HMS Verscan) 기법을 제안하여 수치 실험을 수행하였다. 수치실험을 위해 HMS 운용환경에 근접한 고주파 음선모델(BELLHOP)과 잔향음 모델(HYREV)을 이용하였다. 그 결과 HMS Verscan 기법은 수평방향의 음파방사에 의해 주로 발생하는 근거리 음영구역으로 해저반사를 통하여 음파를 전달시켰고, 근거리 음영 구역에 숨어있는 표적의 탐지가능성을 높였다. 또한 실제 산란환경을 고려한 수치실험 결과에서도 부분적으로 표적이 탐지가 됨으로써 HMS Verscan 기법의 근거리 음영구역의 감소효과를 확인하였다.

• The Journal of the Acoustical Society of Korea
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• v.20 no.4
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• pp.81-86
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• 2001

126-kHz bistatic sea surface scattering measurements were conducted in the shallow waters off the east coasts of Korea. The range from source to receiver was altered to change the scattering angle at the grazing angles of 38％ and 52％ . Unlike bottom scattering signal, the arrival time and the amplitude of sea surface scattering signals were varied due to the fluctuation of sea surface. The measured forward scattering strengths were compared to model predictions of Kirchhoff approximation and small slope approximation. In overall, the tendency of the scattering strengths showed reasonable agreement among the experimental data, Kirchhoff approximation, and small slope approximation.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.8
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• pp.823-831
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• 2008

Since it needs the light computational load and small database, sound source localization method using time delay of arrival(TDOA method) is applied at many research fields such as a robot auditory system, teleconferencing and so on. Researches for time delay estimation, which is the most important thing of TDOA method, had been studied broadly. However studies about factors for time delay estimation are insufficient, especially in case of real environment application. In 1997, Brandstein and Silverman announced that performance of time delay estimation deteriorates as reverberant time of room increases. Even though reverberant time of room is same, performance of estimation is different as the specific part of signals. In order to know that reason, we studied and analyzed the factors for time delay estimation using speech signal and room impulse response. In result, we can know that performance of time delay estimation is changed by different R/D ratio and signal characteristics in spite of same reverberant time. Also, we define the performance index(PI) to show a similar tendency to R/D ratio, and propose the method to improve the performance of time delay estimation with PI.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.1
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• pp.32-37
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• 2011

Underwater communication is affected by reverberation and noise characteristics of the underwater channel and time delay takes place by multipath. Hence, Signal is distorted and a lot of error is generated in the transmitting/receiving by multipath effects, so a channel coding for error correction is required. We propose a channel coding algorithm which is possible to correct error of received signal. We compare and analyze BER(bit error rate) performance depending on the depth of each transmitter-receiver using channel coding algorithm. QPSK was used as a modulation method, and 1/2 code rate convolution coding was used as a coding rate. A convolution coding method shows increase of BER performances.

• The Journal of the Acoustical Society of Korea
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• v.22 no.1
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• pp.78-87
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• 2003

High-frequency (126-㎑) bottom backscattering measurements with various bottom types were conducted at the water tank in Ocean Acoustic Laboratory, Hanyang University. For the purpose of investigating the energy distribution of bottom scattering with various bottom types, the sediment was varied with gravel, sand, sandy mud and mixed bottoms. To examine the anisotropic nature of the scattering due to the orientations of bottom ripple, the footprints were made transverse and longitudinal to the direction of incident wave. The total scattering characteristics are that the larger grazing angles the larger backscattering strengths become and backscattering strengths for a transverse ripple case are higher than those of longitudinal ripple case. finally, the variations of scattering strength depend mainly on the ripple's orientation.

• The Journal of the Acoustical Society of Korea
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• v.21 no.4
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• pp.421-429
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• 2002

Sea surface backscattering signal measurements were conducted in the shallow waters off the east coast of Korea to study the acoustic wave scattering from the sea surface. The grazing angles of wave range from 20° to 40° with a frequency of 60 kHz. The wind speed and surface roughness of the experiment area were 3 m/os and below 1 m, respectively. The measured acoustic backscattering strengths greatly exceed the composite roughness predictions at low grazing angles. To account for this discrepancy, the scattering strengths due to a near-surface bubble layer were considered. The prediction with bubble contribution was found to be in good agreement with the experimental measurement.

• The Journal of the Acoustical Society of Korea
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• v.31 no.4
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• pp.205-213
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• 2012

Active acoustic array signal was measured in the East Sea and the South sea and spatial coherence was analyzed. The measurement of ambient noise, target reflection signal, sea surface backscattering signals took place including environmental measurements of sea wind, and vertical temperature profiles. The spatial coherence of ambient noise was lower than that of target reflection signal in the South Sea. The spatial coherence of target reflection signal was above 0.5 over all array length. The spatial coherence of sea surface backscattering signal was higher in high incident angle. The maximum non-dimensional array length was 3.0 ($26^{\circ}$) and 3.5 ($32^{\circ}$) to have spatial coherence above 0.5 in the East Sea. To find a design criteria for array configuration and array performance, more measurements of temporal and spatial coherence will be needed continuously in the future.