• Proceedings of the Korean Institute of Interior Design Conference
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• 2007.05a
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• pp.85-88
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• 2007

This research is a case study for improving the sound environmental quality of cafeteria in university campus. The purpose of the study is to investigate the present condition of physical level, type, and source of indoor noise by comparison with a restaurant near campus. Methods were field survey with measurement on equivalent and instant noise level and observation on noise type, and questionnaire survey to 60 students users. Surveys were carried out in the 8th and the 14th of December 2005. The results are as follows. 1) Indoor noise levels of the cafeteria were measured as $67.2{\sim}76.6$(average 73.3) dB(A)Leq5min and $60.3{\sim}90.5$(average 71.2) dB(A), but noise levels of the restaurant were $61.6{\sim}70.4$(average 66.9) dB(A)Leq5min and $59.8{\sim}70.6$(average 64.9) dB(A). 2) The users's responses on major noise type were 'noise by handling equipment and tableware', 'noise by moving chairs', and 'taking noise' in cafeteria, but 'taking noise' and 'background music' in restaurant. 3) It was found that the differences of indoor noise condition between with 2 subjects were caused by finishing materials, kitchen division type, and furniture type.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.259-262
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• 2006

This paper introduces the process of reducing the automobile wind noise by using acoustic holography. First, a microphone array scans a side or plane under an automible step-by-step. Second, a pressure on a source plane is calculated. Third process is to analyze how much individual sources contribute to interior noise. Fourth process is to control important noise sources determined by the contribution analysis. This paper deals with the entire process, theoretical and experimental problems.

• International Journal of Automotive Technology
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• v.7 no.2
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• pp.173-177
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• 2006

A noise transfer function(NTF) is the frequency response function between an input force applied to an exterior point of a vehicle body and the resultant interior sound pressure usually measured at the driver's ear position. It represents the measure of noise sensitivity for the output force transmitted to the joints between the body and chassis. The principle of vibro-acoustic reciprocity is often utilized in the measurement of NTF. One difficulty in using the volume source is that most of the previously proposed methods require the knowledge of the volume velocity of the acoustic source in advance. A new method proposed in the present work does not require any calculation related with the volume velocity of the acoustic source, but still yields even more accurate results both in the amplitude and phase of the NTF. In the present work, the new method is applied to obtain NTF data for a midsize sedan.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.318-321
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• 2005

In vibro-acoustic analysis, the commercial CAE tools, such as SYSNOISE, is usually used to take into account of the coupled effects of fluid acoustics and structural vibration. The acoustic field can be solved by either FEM or BEM, while the vibration field is usually solved by FEM. The interior or exterior acoustic problems with the coupled effects of the structural boundary could be solved by the commercial tools. The commercial tools, however, could not solve the problems in case that both the interior and exterior acoustic field is coupled with the structural boundary. In this paper, a realistic method based on FEM/BEM coupling scheme is presented to analyze the acoustic radiation from the internal source in a chamber to external acoustic field through elastic structural boundary. Several numerical examples are implemented to validate the developed program.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.687-691
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• 2007

It is important to increase the sound proof performance of building for reducing the influence of aircraft noise on the bais of actual survey of existed buildings. The purpose of this study is to propose the basic data for designing sound insulation of residential house. In this study, field measurement of aircraft noise Interior and outside noise level difference were carried out for 7 days in 2 residential houses. As the result, aircraft noise levels showed to be Leq $71.8{\sim}74.5$dB(A), WECPNL $82.2{\sim}83.4$ and indoor noise level were NC-55 ${\sim}63$ over acceptable NC-30 in 2 measured houses. Noise reduction effect showed to be $15.8{\sim}23.1$dB(A) in measured houses, and houses with double window were preferable to those with single window in sound proof performance. The outside sound pressure level for residential house was a little different according to the type of source. In measuring by using aircraft noise it was effected by angle and distance from measuring point, to aircraft, window area, and sound absorption of room, and so on.

• Proceedings of the KSR Conference
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• 1998.11a
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• pp.388-397
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• 1998

This paper gives the way of analyzing internal noise of rolling stocks which is urgently required by civilians. Triangular beam method among ray tracing techniques is utilized to compute noise distribution of rolling stocks. Noise source and transmisstion loss of several sections from experimental work are included in this calculation. Ray tracing technique is found useful to compute big structures like rolling stocks.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.3
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• pp.40-49
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• 1996

With the advance of the standard of living, the demand on automobile goes beyond the simple transportion equipment, therefore the interior noise reduction has been the important factor for improvement of the ride quality. Idling noise is a major vehicle characteristic determining occupant comfort. In the present research two approaches for noise source identification based on theory for multi-input system have been investigated. The concept of the frequency response function and the multi-dimensional spectral analysis were used to estimated the spectra of the noise source.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.486-489
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• 2004

The NAH based on the inverse BEM is used to reconstruct the source field, which is advantageous in dealing with the irregular source. In the implementation of this technique, a large number of pressure measurements is required because an over-determined pressure data set is required. These conditions accordingly cause the increase of measurement time and associated effort along with the error due to mal-positioning. The purpose of this study is to reduce such inconveniences: Instead of increasing the number of field pressure data, the number of transfer paths between the source and the receiver is increased by placing rigid scattering body in-between the source and receiver. For validating the usefulness and effectiveness of the method, the numerical analyses of interior problem are demonstrated. As a result, it is thought that the proposed method enables the measurement at smaller number of sensor positions and the monitoring of surface vibration with less experimental effects than before.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.6
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• pp.550-555
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• 2012

Among the various elements affecting a customer's evaluation of automobile quality, buzz, squeak and rattle(BSR) have been considered to be major factors. In most vehicle manufacturers, the BSR problems are solved by find-fix method with the vehicle road test, mainly due to various excitation sources, complex generation mechanism and subjective response. To systematically tackle the BSR problems in early stage of the vehicle development cycle, these difficulties should be resolved. The aim of the present paper is to characterize the sound quality property of BSR noise that can be used to assess the subjective responses to BSR. The four sound metrics from Zwicker's sound quality parameter are computed for the signals recorded for eight BSR noise source regions localized by using the acoustic-field visualized results. Then, the jury test of BSR noise are performed. On the basis of the computed sound metrics and jury test result is evaluated to represent the harshness of BSR noise. It is expected that the developed BSR measuring system and sound quality properties can be used to reduce the automotive interior BSR noise in terms of subjective levels as well as objective levels.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.629-633
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• 2005

The reduction of the Vehicle interior noise has been the main interest of NVH engineers. The driver's perception on the vehicle noise is affected largely by psychoacoustic characteristic of the noise as well as the SPL. In particular, the HVAC sound among the vehicle interior noise has been reflected sensitively in the side of psychology. In previous study, we have developed to verify identification of source for the vehicle HVAC system through multiple-dimensional spectral analysis. Also we carried out objective assessments on the vehicle HVAC noises and subjective assessments have been already performed with 30 subjects. In this study, the linear regression models were obtained for the subjective evaluation and the sound quality metrics. The regression procedure also allows you to produce diagnostic statistics to evaluate the regression estimates including appropriation and accuracy. Appropriation of regression model is necessary to $R^2$ value and F-value. And testing for regression model is necessary to Independence, Homoscedesticity and Normality. Also we selected optimum layout of damping material using Taguchi method. As a result of application, sound quality is improved by more quiet, powerful, expensive, smooth.