• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.241-244
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• 2002

시간영역에서의 음원 방향 추정 알고리즘을 이용하여 수동형 DIFAR Sonobuoy 의 도래각 추정 성능 평가 시스템을 구성하고 추정 오차에 대하여 고찰하였다. 일반 실내에서 음원주파수 $f_0(700Hz\~1.7kHz)$로 입사하는 음원에 대하여 도래각을 추정한 결과 한 주기당 한계 ${\pm}10^{\circ}$ 이내로 약 $80\%$ 이상 추정 결과로 나타났으며 특히, 1.7kHz 의 경우는 ${\pm}2.97^{\circ}$로 적은 오차를 보임에 따라 이 대역에서의 기준 주파수로 평가 시스템에 적용할 수 있음을 확인하였다.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.1
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• pp.229-234
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• 2013

As the popularization and proliferation of smart phone and location based services, the necessity and importance of the location based service based on the smart phone becomes significant. But existing technologies could not be applied in real situation due to the lack of accuracy, economy, and convenience, the method using the signal strength of WLAN is not accurate. In this paper, the technical back ground, implementation issue, and measurement result are described for the proposed relative positioning technology using acoustic signal and Bluetooth with smart phone. It is possible to measure the position of the smart phone with accuracy and simple device, and it is very proper especially for the indoor location based intelligent services.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.1
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• pp.74-82
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• 2010

Power flow analysis(PFA) methods have shown many advantages in noise predictions and vibration analysis in medium-to-high frequency ranges. Applying the finite element technique to PFA has produced power flow finite element method(PFFEM) that can be effectively used for analysis of vibration of complicated structures. PFADS(power flow analysis design system) based on PFFEM as the vibration analysis program has been developed for vibration predictions and analysis of coupled structural systems. In this paper, to improve the function of vibro-acoustic coupled analysis in PFADS, the PFFEM has been extended for analysis of the interior noise problems in the vibro-acoustic fully coupled systems. The vibro-acoustic fully coupled PFFEM formulation based on energy coupled relations is extended to structural system model by using appropriate modifications to structural-structural, structural-acoustic and acoustic-acoustic joint matrices. It has been applied to prediction of the interior noise in two room model coupled with panels, and the PFFEM results are compared to those of statistical energy analysis(SEA).

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.1
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• pp.13-21
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• 1992

In the previous study, car interior noise was analyzed using structural acoustic mode coupling coefficients and noise response in vehicle compartment model was simulated by the developed special purpose program. As a continued study, this paper presents a practical scheme for the interior noise reduction of a passenger car. Noisy panels on the vehicle compartment wall could be easily identified by the analysis using mode coupling coefficients. Numerical simulation for noise reduction was carried out on a simplified vehicle compartment model by using panel contribution factor and the noise reduction effect was verified by the structural modification test using Steel Skin (damping sheet).

• Journal of Satellite, Information and Communications
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• v.8 no.4
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• pp.30-36
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• 2013

Recently the globalization of the media content industry, various activities have been made in the field of art and the speaker system is very important in the sound industry which is one of the arts. The directional characteristics of a loudspeaker refer to the radiation of sound in certain directions and are among the most important features of a loudspeaker. Designing a loudspeaker that can keep all of its constant directivity at all frequencies is difficult due to the wavelengths of audio frequencies and the size of horns and transducers. This study proposed gradient array methods to improve low frequency pattern control of full-range speakers to maximize Direct to Reverberant Ratios at the listeners.

• The Journal of the Acoustical Society of Korea
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• v.22 no.3
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• pp.162-168
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• 2003

The degree of diffusion, characterized by the "scattering coefficient" of surface materials, has been known to be one of the most important factors in determining the acoustical qualities of concert halls. Based on the suggested ISO method, which measures the random-incidence scattering coefficient of surfaces in a diffuse field, the scattering coefficients of different sizes and densities of wooden hemispheres and cubes were measured in model-scale reverberation rooms. As a result, wooden hemispheres with a structural depth of more than 15㎝ have the highest average (500㎐∼4㎑) scattering coefficient. It was also found that the scattering coefficient becomes higher when the diffuser density reaches about 50% for hemispheres and 30% for cubes.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.5
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• pp.394-400
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• 2018

Various numerical methods have been adopted for indoor noise assessments of ship plant. Acoustical radiosity method is one of the high frequency approaches for acoustic field analysis, which assumes diffuse reflections by boundaries so that it could be efficiently applied to the acoustically diffused indoor space noise analysis. In this study, an acoustic field analysis program has been developed based on radiosity method, which could apply for acoustically large enclosures such as ship's indoor space. For this purpose, the procedure of the acoustical radiosity method has been summarized and implemented to an acoustic field analysis program using MATLAB. Numerical example for a rectangular indoor space has investigated validity of the implemented program. Steady state sound pressure levels calculated for a continuous acoustic source signal have shown good agreement with those by other solutions such as an analytic solution and a ray tracing method. Instantaneous sound pressure levels calculated for an impulsive acoustic signal have provided the clues of direct/reflected acoustic field and reverberation time.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.254-257
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• 2010

Acoustic design parameters of a Helmholtz resonator are studied experimentally and numerically for acoustic stability in a model acoustic tube. Acoustic damping is quantified by the amplitude of the fluid velocity in mass-spring-damper system. The length of an orifice, the volume of a cavity, and the diameters of an orifice and a cavity in the resonator are selected as design parameters for tuning of the resonator. It is found that acoustic damping capacity is increased by shorter orifice and longer cavity in the resonator. As the ratio of the orifice diameter to the cavity diameter increases in the resonator, the damping capacity decreases.

• Journal of Navigation and Port Research
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• v.37 no.3
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• pp.269-273
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• 2013

Underwater acoustic channels are generally recognized as one of the most difficult communication media because of the multipath propagation, dispersion, and so on. MIMO (Multiple-input multiple-output) techniques have been actively pursued in underwater acoustic communications recently to increase the data rate over the bandwidth-limited channels. The transmit diversity techniques can be applied in this case, and one of them is Alamouti's scheme. In this paper the performances of the transmit diversity technique are evaluated via experiment. Two transmitters and two receivers were used in experiment, and the experiment was performed in indoor water tank. The error rate 5~8% was confirmed in experimental results, and these are the improved values than the error rate 14.8% for SISO(Single-input single-output) channel under same data rate condition.

• The Journal of the Acoustical Society of Korea
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• v.7 no.2
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• pp.26-38
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• 1988

This paper describes three methods for the estimation of the impulse reponse in an indoor acoustic transfer system which rather has long reverberation time by the cross spectrum. The first method, which is the conventional one, will use the white noise as the source signal. Therefore, the very long time window data and numerous number of DFT are necessary for this estimation. The second method has been disigned in order to shorten the length of time window of the first method by using a burst of noise as the source signal. The third method which will be suggested in this paper uses too types of definite signal with short duration time of the source signal. According to the view point of computation capacity, and estimation accuracy of the impulse response, the compared experimental results show that the third method will be better than the others.