• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.761-762
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• 2012

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.06d
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• pp.18-24
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• 1998

최근의 연구를 통해 해양의 내부파가 음파전달에 영향을 주어 비정상적인 손실을 일으키는 것을 밝혀졌다. 한국 동해세서도 강한 수온약층을 중심으로 내부파가 존재할 것으로 여겨져 왔으며, 이를 규명하고자 '98년 6월 각종 장비를 동원한 해양 관측을 동해항 근해에서 실시하였다. 또한 내부파에 의한 음파의 전파 특성을 추정학자 음원과 수신기를 고정한 상태에서 음향 실험을 실시하였다. 실험 결과 전형적인 내부파는 주기가 약 5-12분이고 최대 진폭은 15m 정도임이 밝혀졌다. 특히 10여개의 내부파 묶음이 약 36cm/sec 의 속도로 이동하고 있음도 확인하였다. 15개의 음향센서로 이뤄진 수직선배열 수신기와 음원을 이용한 음향 실험결과 역시 4-12분 주기에서 부분적으로 스펙트럼이 높게 나타났으며, 특히 주파수 1kHz 인 경우에는 4, 6분 주기에서 15개의 센서에 대해 일관되게 높은 스펙트럼 준위가 나타났다. 내부파에 의한 이러한 음파의 특성은 음파의 모든간 결함으로 나타나는 일종의 간섭 현상으로 설명될 수 있다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.10
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• pp.1656-1665
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• 1997

The intake noise, a major source of vehicle noises, has rapidly become a noticeable, and has been studied to reduce the level. Traditionally, the intake system has been developed through a experiment, namely, the trial and error process. This approach requires very high cost and long time consuming to develop the systm. Recently, FEM and BEM are becoming useful in analysis of the intake system, and the results of analysis are very valid. But because this techniques also require high cost and long analysis time, this technique is generally not practical tool at the early stage of the development. In this study, the software was developed to predict and analyze the acoustic characteristics of the intake system. It was based on the Transfer Matrix Method and operated to analyze a simplified intake system in a personal computer. It can be used early in the design stage of development of the intake system. This study presented a improvement to reduce the level of the intake noise, which modified the specification of the intake system. And the improvement were verified by NIT/SYSNOISE, FE analysis commercial software, and testing a prototype.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.996-1000
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• 2002

A porous tube, comprised of a resin-coated woven fabric has recently been used as an effective component for use in intake systems of internal combustion engines to reduce the intake roaring. For the prediction of the acoustic performance of an engine intake system with a porous woven hose, the acoustic wall impedance of the hose must be known. Because of its peculiar acoustical and structural characteristics, the accurate measurement of the wall impedance ofa porous woven hose is not easy. A new measurement technique is proposed herein, that is valid over the low to mid frequency ranges. The acoustics impedance is inversely estimated from an overdetermined set of measured pressure transmission coefficients for specimens of different lengths and the reflection coefficient of end termination. The method involves only one measurement, and, as a result, it is very simple. The measured TL for samples with arbitrary conditions, arbitrary porous frequency, arbitrary length, and arbitrary mean flow condition, are in reasonably good agreement with values predicted from curve-fitted impedance data.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.8
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• pp.1465-1471
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• 2007

The electro-magnetic wave propagates through the air in the terrestrial communications, but the acoustic wave propagates through the seawater in the underwater acoustic communication(UAC). It makes the differences between the UAC link and the well hon air communication links. In this paper, we have studied path loss, absorption and ambient noise of the ocean as a medium for UAC. We have analyzed the absorption coefficient and ambient noise level of the coastal area of South Korea and suggested a strategy for the selection of the frequency band by considering the absorption coefficient and ambient noise level. Also, we present an illustrative example of a link budget for the QPSK UAC system which has carrier frequency 25kHz, bit rate 10kbps, range 1km and BER $10^{-3}$ in the shallow water environment with an ideal AWGN assumption.

• The Journal of the Acoustical Society of Korea
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• v.42 no.6
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• pp.572-583
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• 2023

Demand for wood in construction is increasing worldwide. In Korea, technical reviews of high-rise Cross Laminated Timber (CLT) buildings are under way. In this paper, Floor Impact Sound Insulation Performance (FISIP) and Transmission Loss (TL) of 150 mm thick CLT floor panels made of two domestic species, Larix kaempferi and Pinus densiflora, are investigated. The CLT slabs were tested in reverberation chambers connected vertically. When comparing Single Number Quantity (SNQ) of FISIP of the bare panels, the Larix CLT is 3 dB lower in heavy-weight and 1 dB in light-weight than the Pinus CLT. However, there was no difference when concrete toppings were added to improve the performance. As the concrete toppings became thicker, the heavy-weight was reduced by 9 dB ~ 20 dB, and the light-weight by 20 dB ~ 30 dB. And the analysis of these results with area density has confirmed that the area densities are highly correlated (R² = 0.94 ~ 0.99) to the FISIP of the CLT. The types of CLT didn't affect the TL. Comparison of theoretical TL values with measured TL values has shown that the frequency characteristics are similar but 8 dB ~ 12 dB lower in measured values. The relationship between the TL and frequency characteristics of the tested CLT slabs was derived by using the correction value.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.11
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• pp.1013-1020
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• 2007

In this paper, the predictions and measurements of sound transmission loss(STL) are discussed for various types of acoustical materials and carpets. Random incidence sound transmission losses are measured by the sound intensity method. The in-house software HONUS2005 is used to predict TL and estimate the various physical properties such as the flow resistivity, the structure factor, the porosity, the Possion's ratio, and etc. After this estimation, various multi-layered materials with a steel plate are measured and predicted. In particular, Carpets are assumed to be membranes to predict acoustical performance. To confirm this assumption, double and triple-layered cases are also observed including two different kinds of carpets.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.2
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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.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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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.

• The Journal of the Acoustical Society of Korea
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• v.36 no.5
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• pp.329-337
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• 2017

In USA and UK, the standards of both reverberation time and background noise level have been established for the appropriate aural environment in classrooms. In order to realize this, guidelines for architectural planning and interior finishing have been also suggested. However, in Korea, there has hardly been any guidelines for satisfying background noise criteria and investigation about sound insulation performance of current walls of classrooms. The present study investigates the structure of outer wall and walls between classrooms of two middle schools in order to analyze the sound insulation performance against both exterior and interior noises. Acoustic parameters including transmission loss, standardized sound level difference, and signal to noise ratio have been measured and analyzed for sound insulation performance of walls and flanking noises. As a result, concerning the walls in between classrooms, it was found that walls of dry construction have greater sound insulation performance rather than the walls of wet construction especially in mid and high frequency bands. Also, It was revealed that thermopane, insulated pair glass, of outer walls, has greater sound insulation performance than the double window consisted of two single pane glass. Regarding flanking noises, the standards were exceeded when all windows, or windows and doors front onto corridor were opened. It denotes that students could be disturbed with the sound transmission by the interior noises.