• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.880-884
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• 2014

RT (reverberation time) of outdoor spaces surrounded by multi-storey buildings depends on many designable factors such as the openness, volume and building layouts, etc. This study therefore aims to clarify the influential factors for RT in outdoor spaces surrounded by buildings with complicated topographical conditions. A series of measurements were carried out for 15 outdoor spaces in 6 apartment complexes with different building layouts. An Empirical method considering the openness, averaged ray length and building high is also suggested, to predict RT approximately in the outdoor spaces. The overall results suggest that RT in outdoor spaces of apartment complexes is significantly influenced by source-receiver distance and building layouts.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.669-674
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• 1997

A sound field in a reverberation room is analyzed by using numerical methods and the SPL distributions are compared to the measurements. In numerical predictions, the BEM is employed in the low frequency range, while sound ray tracing method is used for the high frequency range. In the BEM analysis, the surfaces of the empty reverberation room are assumed as rigid boundaries and the damping coefficients are estimated from the measured absorption coefficient. The comparisons with measurements for 100Hz shows good agreement. In the sound ray tracing analysis, the predicted energy decay are in excellent agreements with theoretical results. It is shown that the energy absorption by air damping plays an important role as frequency becomes higher.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1376-1378
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• 2006

Numerical and experimental study were carried out to characterize sound fields of low frequency in a scaled reverberation chamber for measurement of sound insulation of panels. By using BEM, lower modes of the chamber are identified and then predicted the effect of diffusers in order to destruct lower modes. Compared results with measurements show reasonable agreements, especially at the first end second modes. Based on numerical prediction, the diffuser are installed in order to improve sound fields to be more diffuse than ever. It is found that the diffuser put in nodal line of the chamber destruct evidently the first mode. Consequently, the measuring error at the low frequency can be relatively reduced compare to the case of without diffuser.

• Journal of the Korean Institute of Navigation
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• v.22 no.3
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• pp.27-34
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• 1998

The paper is the second part on the 3-D sound-field creation implementing the Virtual Reality Ship Handling Simyulator(VRSHS). As mentioned in the previous part Ⅰ, the spatial impression, which arose from reproduced 3-D sound-field , give natural sound environmental context to a listener. This spatial impression is due to the reverberation by reflections and ,is can be obtain by using Head-Related Transfer Function(HRTF). In this work, we foumulate early and late reverberation models of the HRTF's with theoretical control factors based on the sound-energy distribution in an irregularly shaped enclosures. Using the reverberation models, we report results from psychophysical tests used to asses the validity of the proposed 3-D soud-field control method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.786-790
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• 2003

The purpose of this research is to observe that the acoustic characters of classroom have some difference by several conditions. TSP has used to measure impulse response and such physical indexes as RT(Reverberation Time), D$\sub$50/, and STI(Speech-Transmission-Index) are computed by it. we investigate difference under some conditions such as when students were present at each classroom and when was not so, and when professor used a microphone and unused it. In this study, we found that reverberation time when people take a seat is lower than was not so. we wish to help one who work for construction industry, as they build a kind of classroom

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.797-801
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• 2003

The Statistical Energy Analysis is based on the power flow and the energy conservation between sub-systems, which enable the prediction of acoustic and structural vibration behavior in mid-high frequency ranges. This paper discusses the identification of SEA coupling loss factor parameters from experimental measurements of small reverberation chamber sound pressure levels and structural accelerations. As structural subsystems, steel plates with and without damping treatment are considered. Calculated CLFs were verified by both transmission loss values for air-borne CLF case and running SEA commercial software As a result, CLFs have shown a good agreement with those computed by software. Acoustical behavior of air-borne noise and structure-borne noise has been examined. which shows reasonable results, too.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.11
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• pp.83-88
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• 2011

The spectral field data on the observation planes inside a mode stirred chamber have been computed by using the FDTD method. They can describe the directional dependence of all supported modes in the reverberation chamber (RC). Correlation coefficients have been found to evaluate the stirring effects. The correlation coefficients were obtained and compared for three different sizes of stirrers and statistical uniformity was investigated.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.10
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• pp.917-924
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• 2012

Noise power of large machineries, such as textile looms, winders, and twisting machines, is often measured in a reverberant space because they cannot be installed and operated in an anechoic chamber due to their size, weight, and operating conditions. Factors affecting the measurement error of an in-situ noise power measurement include the nonuniform reverberation time and the direction of sound intensity vector which is usually regarded as normal to the measurement surface. In this study errors due to these factors are estimated with the aid of numerical simulation based on the ray-tracing technique. The averaging of reverberation times measured at several points on the measurement surface is suggested to reduce the errors from nonuniform absorption. Also the direction cosine of each surface element is taken into account, which as a whole is represented as a solid angle of the measurement surface.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.686-689
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• 2005

This study aims to analyzed the acoustics characteristics of Korean Traditional Houses in Chonnam Province varied with lay out and floor plane to reflect the way of control for environmental condition. These houses are surveyed the reverberation time and level difference between rooms of the main living room and other main floored room, master room and kitchen. As a result, the reverberation time of traditional rooms are below 0.6 second, and the sound insulation performance of Korean traditional door are mostly very low grade with D-15. The level difference between rooms are low grade not to meet minimum class except between main living room and master room away from main living building.

• Journal of Korean Association for Spatial Structures
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• v.8 no.3
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• pp.65-73
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• 2008

The present work deals with subjective assessments to propose the objective parameter related to the subjective attribute of reverberation in the coupled room varied the aperture opening size. A 1/10 scale model was built and used for the measurements and subjective assessments. For the subjective tests, binaural impulse responses(BIRs) were measured using a dummy head and the measured BIRs were convolved with anechoic recorded music for the presentation over the headphones. The results showed that the perceived reverberation was the largest in the aperture opening size 12.5%(1.97% of mail) room surface area)and decreased with increasing the aperture opening size over 25% (3.94% of main room surface area) in the main room coupled with the secondary reverberant room. In the main room coupled with the secondary absorptive room, there was no changes in the perceived reverberation up to the aperture opening size 6.25%(0.99% of main room surface area) and it gradually decreased with increasing the aperture opening site over 12.5%. The objective parameter, T30/T15, showed a very low correlation with the perceived reverberation in the coupled room varied the aperture opening size but showed a high correlation with a new objective parameter, T30/Tbp, proposed by the authors. Because the late part decay energy more rapidly increases with increasing the aperture opening site than the early and middle part decay energy, the LDT/EDT or T3/T1 is a better quantifier to measure double slopes in the coupled room than the T30/T15.