• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1996.10a
• /
• pp.153-159
• /
• 1996

The acoustic characteristics of a direct radiator type loudspeaker has been studied in this paper. The vibration displacement of the speaker cone paper obtained by the finite element analysis has been converted into the vibration velocity and used as a boundary condition for the acoustic analysis. The frequency characteristics and the sound pressure distribution of the loudspeaker resulted from the radiation of the cone vibration have been calculated by the boundary element analysis. The numerical results have been verified by experiments carried out in an anechoic chamber. The variations of the acoustic characteristics due to the changes of some design parameters have been examined using the numerical model.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2004.11a
• /
• pp.166-169
• /
• 2004

In this paper, computational analysis and experiments of subwoofer for car audio speaker system were performed and discussed to analyze acoustical phenomena for subwoofer. Ported enclosure system with subwoofer were manufactured and provided for test and simulation purposes. Subwoofer with single voice coil and double voice coil were identified by linear and nonlinear parameter identification method for loudspeaker parameters. For high power inputs to subwoofer, sound pressure levels were compared according to input powers with linear and nonlinear loudspeaker models. For subwoofer system with high power nonlinear speaker model was showed to be adequate to describe the behaviour of loudspeaker.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2000.11a
• /
• pp.489-494
• /
• 2000

제품과 사용자간에 필연적으로 존재하는 소리를 쾌적하게 하기 위한 연구로서 자연음 6종과 소음 6종의 음압(dB)이 비슷하도록 조절하였을 때 소리의 어떠한 물리적 특성이 긍/부정감성에 주된 영향을 미치는지를 파악하기 위하여 남/녀 각각 35명씩의 대학생들에게 7점척도의 8가지 형용사 쌍을 이용한 음질평가 청감실험을 한 결과 물소리를 포함한 자연음은 소음보다 대체로 긍정감성이 높게 평가되었고 긍정감성과 심리음향인자와의 상관성은 Loudness의 -0.37을 비롯하여 "-"상관성을, Unbiased annoyance와 심리음향인자들과의 상관성은 Loudness의 0.92를 비롯한 "+" 상관성을 각각 갖었으며 여자는 남자보다 긍/부정감성에 더욱 예민하게 반응하는 것으로 나타났다.

• Proceedings of the KSR Conference
• /
• 1998.11a
• /
• pp.369-378
• /
• 1998

When a high-speed train enters a tunnel, a compression wave is generated ahead of the train and propagates along the tunnel. This wave subsequently emerges form the exit portal of the tunnel, which causes an impulsive noise. In the present study, experimental investigation is carried out on the sonic boom noise with parameters of train speed, blockage ratio, nose shape of train and airshaft. These experimental results show that several countermeasures could be used to efficiently reduce the sonic boom. In addition, numerical analysis is performed to predict the sonic boom. The predicted sound waves are in a good agreement with the experimental results.

• Proceedings of the KSR Conference
• /
• 2008.11b
• /
• pp.1435-1440
• /
• 2008

High-speed train under development is a type of EMU(electric multiple units). Since power sources like motors and gears are distributed in the high-speed EMU, the high-speed EMU generates vibration and sound more than the articulated high-speed train. Vibration of vehicle, vibration between rails and wheels, hunting of bogie and snake motion reduce ride comfort. In this paper, to decrease the vibration of the articulated high-speed train, improvements were presented using an analytical model and a simulation model. The simulation model of the high-speed EMU was designed on the basis of the korean high-speed train and the design parameters for ride comfort were showed and the dynamic characteristics of the vehicle was understood. To consider the characteristics of the vehicle suspension, the analytical model was designed and the simulation model was verified with it.

• The Journal of the Acoustical Society of Korea
• /
• v.40 no.3
• /
• pp.241-246
• /
• 2021

Modern loudspeaker systems are changing an active loudspeaker system that have multiple input channels and power amplifier. So, we cannot measure these active loudspeakers with IEC 60268-5 standard. This paper introduces an IEC 60268-21 standard that can measure an active loudspeaker having many analog and digital and wireless or wired inputs and having various control parameters.

• Journal of the Korean GEO-environmental Society
• /
• v.23 no.1
• /
• pp.15-23
• /
• 2022

This paper presents the results of full-scale load tests performed frictional anchors to various lengths at several sites in Korea. Various rock types were tested, ranging from highly weathered shale to sound gneiss. In many tests, rock failure was reached and the ultimate loads were recorded along with observations of the shape and extent of the failure surface. Laboratory tests were also conducted to investigate the influence of the corrosion protection sheath on the bond strength. Based on test results, the main parameters governing the uplift capacity of the rock anchor system were determined. By evaluation of the ultimate uplift capacity of anchor foundations in a wide range of in situ rock masses, rock classification suitable for structural foundation was developed. Finally, a very simple and economical design procedure is proposed for rock anchor foundations subjected to uplift tensile loads.

• Journal of ILASS-Korea
• /
• v.26 no.4
• /
• pp.182-188
• /
• 2021

In this paper, using a transfer function-based analytical model, major factors influencing the acoustics and combustion instability in a two-stage duct system composed of a nozzle and a combustor were derived and their quantitative effects were evaluated. From the acoustic analysis, it was confirmed that the change in reflection coefficient and mean flow could have a great influence on the instability growth rate, and the area ratio and speed of sound ratio between the nozzle and the combustor are also key parameters to determine combustion instability as well as flame transfer functions.

• Korean Journal of Radiology
• /
• v.23 no.1
• /
• pp.13-29
• /
• 2022

Nonalcoholic fatty liver disease, characterized by excessive accumulation of fat in the liver, is the most common chronic liver disease worldwide. The current standard for the detection of hepatic steatosis is liver biopsy; however, it is limited by invasiveness and sampling errors. Accordingly, MR spectroscopy and proton density fat fraction obtained with MRI have been accepted as non-invasive modalities for quantifying hepatic steatosis. Recently, various quantitative ultrasonography techniques have been developed and validated for the quantification of hepatic steatosis. These techniques measure various acoustic parameters, including attenuation coefficient, backscatter coefficient and speckle statistics, speed of sound, and shear wave elastography metrics. In this article, we introduce several representative quantitative ultrasonography techniques and their diagnostic value for the detection of hepatic steatosis.

• The Journal of the Acoustical Society of Korea
• /
• v.30 no.7
• /
• pp.390-395
• /
• 2011

This paper covers the studies on common voice parameters through the voice analysis of female main news anchors on weekday evening by the station, and differences of relative voices and sounds among stations. To examine voice characteristics, 6 voice parameters were analyzed and it showed anchors of each station had distinctive characteristics of voices and phonations over all fields except the speech rate, and there were also differences in sound systems. As major analysis parameters, basic pitch, tone of the 1st formant and pitch ratio, level of closeness by pitch bandwidth, type of sentence closing through average pitch position within pitch bandwidth, average speech rate, and acoustic tone analysis by energy distribution by frequency band were used. Analyzed values and results could be referred to and utilized in the criteria of phonation characteristics for domestic female news anchors.