• The Journal of the Acoustical Society of Korea
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• v.30 no.5
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• pp.273-280
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• 2011

The sounds of the Korean temple bells, that are located in the various places, were recorded and classified into two groups according to the size of bells. The sound preference was investigated with the subjective listening test on the bells of each group. And the acoustic characteristics of the bells such as the frequency, amplitude, beat period, and 20 dB decay rate of the partials was analyzed. The correlation between the acoustic parameters and timbre preference were analyzed and the acoustic characteristics of highly preferred bell sound were presented.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.1101-1106
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• 2004

This study presents the reconstruction of sound field radiated from an automotive engine using equivalent sources. Basic concept of the method presented is to replace the engine noise source with elementary sources of multipoles, e.g., monopoles and dipoles. The so-called Helmholtz equation least-squares (HELS) method can reconstruct the sound radiation fields from spherical geometries in a series expansion of spherical Hankel functions and spherical harmonics. In this paper, multi-Point, multipole equivalent sources are employed to reconstruct the sound field radiated from an automotive engine with a fixed rotation speed. To ensure and improve the accuracy of reconstruction, the spatial filters of multipole coefficients and wave-vectors are adopted for suppressing the adverse effect of high-order multipoles. Optimal filter shapes are designed with regularization parameters minimizing the generalized cross validation (GCV) function between actual and reproduced model. After regeneration of field pressures using the proposed method as many as necessary, the vibro-acoustic field of an engine could be reconstructed by using the BEM-based near-field acoustic holography (NAH) technique in a cost-effective manner.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.616-621
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• 2006

A began of this study is to verify Spontaneous Acoustic Field Reproduction System(SAFRS), developed as an embodiment of creating agreeable sound environment, with evaluation on the field application. SAFRS is a system to sense changes of surroundings and produce sounds, which can go well with environment elements sensed by the system in to the space. The sound which can go well with environment elements is sound which judged by individual evaluation to be so, the classification of the preferred sounds according to the mood of the space was suggested in the former study. So, SAFRS was applied into the Square of D University to evaluate effectiveness of the system. The executed evaluations were 1) evaluation on sounds perception, frequency, volume and matchability with the space, 2) image evaluation on the square and sound environment and 3) evaluation on sound environment with existing sounds, fountains sound, sound produced by SAFRS, and both fountains sound and sound produced by SAFRS. Verifying SAPRS of field application was deduced from those evaluations. Theresultsofthestudyarefollowing: Though the system was applied into the space, the volume of the sounds shouldn't be too high. And with visual surroundings, the effectiveness of the system would be increased. At the results of four evaluations, the result of day evaluation is; both fountains sound and sound produced by SAFRS>fountains sound>sound produced by SAFRS>existing sounds, the result of night evaluation is; sound produced by SAFRS>both fountains sound and sound produced by SAFRS>fountains sound>existing sounds and these results pointed out that sounds environment produced by the system was highly evaluated due to less background sounds.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.8
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• pp.742-752
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• 2010

In case of the working machine that using in the loud-noisy workplace, as it generates the loud-noise, it is influencing a physical, mental bad effect to those workers. Accordingly, though the noise countermeasure for the loud-noisy workplace is acutely requiring, until now, those methods that wearing the soundproof-protection tool, or restriction the working hours, and minimize the noise exposure volume, were mainly used. However, such noise countermeasures occur many problem points. On such point of view, using the acoustic simulation technique, let the workers to choose the workplace where suffering many damages due to the noise of working machine, and after grasp the physical property of working machine and indoor acoustic characteristic, this Study has attempted to grasp the reduction degree of noise level at before-improvement?after-improvement, through the sound-absorption measure. Passing through such preceding step, using auralizational technique based on the noise of working machine of before-improvement after-improvement, and by conduct psycho-acoustics evaluation, this study intended to investigate the change degree of subject reaction. As the result of evaluation, it is considering that the noise-reduction countermeasure method for the loud-noisy workplace could be much effective, through the sound-absorption measure.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.10
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• pp.1843-1850
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• 2000

Sound absorption coefficient for the absorptive panels comprized of a perforated plate. an absorbent material and an air gap was measured and compared with theoretical value. The absorptive panels are composed of three basic combinations (a perforated plate + an air gap + an absorbent material. a perforated plate + an absorbent material, a perforated plate + an absorbent material + an air gap). As a result. it is found that the sound absorption for low frequency range is strongly affected by the resonance produced by perforated plate and air gap. And the sound absorption for high frequency depends on the porosity of perforated plate.

• Journal of the Korean Institute of Educational Facilities
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• v.11 no.1
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• pp.5-14
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• 2004

Since 1990s in Korea, elementary school classrooms have been designed toward open education system in pursuit of variety of educational purpose. Also, the architectural designs of schools have been acomplished for individual school not based on the standard design code. The present paper aims to investigate the acoustic environment of existing classrooms and to compare the sound insulation capacity between the ordinary classrooms and the newly built classrooms for open education. The current acoustical situation of elementary classrooms was analyzed using field measurements and questionnaire survey. In order to this, Three elementary schools were selected which were built in 1978, 1996 and 2000 respectively. Room acoustical parameters including Reverberation time(RT), Definition(D50), Speech Intelligibility(RASTI), Transmission loss(TL) and STC were measured in a classroom in each elementary school classroom. Each measurement was undertaken with the windows and doors being open or closed. As the result, it was found that the transmission loss between rooms in open classrooms is, $5{\sim}6dB$ in average, inferior than the ordinary classrooms. The RASTI of 0.70 was measured in newly built classrooms which is better than old classrooms(0.70) and open classrooms(0.73). This was shown as same in the speech definition measurements. This results from the condition of sealing and airtightness of classrooms and floor materials. The results denote that open classrooms have poor acoustic condition in sound insulation and speech intelligibility.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.5
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• pp.1573-1581
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• 1996

This paper present as experimental demonstratio of DSP and a sensory actuator that is used to actively control sound transmission/radiation through a vibrating plate. A plane acoustic wave incident on a clamped, thin circular plate was used as a noise source, and a sensory actuator bounded to the plate was used to control and sense vibration of the plate. The sound transmission reduction problem was tranformed as a structural vibration control problem that actively control the structural vibration modes coupled to acoustic modes. The results show that the first structural vibration mode is controlled with a reduction of 78 percent in the displacement and velocity of the plate. This corresponds to a 13dB reduction in the acoustic response. These experimental results indicate that a sensory actuator bounded to the plate can be employed to attenuate the sound transmitted to radiated from the plate.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.515-518
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• 2007

SAFRS(Spontaneous Acoustic Field Reproduction System) is a system to sense changes of surroundings and produce sounds which can go well with environment elements sensed by the system in to the space. The sounds were judged by individual evaluation and, the classification of the preferred sounds according to the mood of the space was suggested in the former study. Effectiveness of SAFRS with field application was validated by prior studies which dealt with researching acoustic environment, evaluating images of sounds, and rating environment with existence and nonexistence of sound resources such as fountains and the system after applied in D university. In this study, for more effective field application of SAFRS, research for the acoustic environment around sound resources and subjective evaluation of the preference of the sounds from the resources were made and it was considered that the results of the experiments should be primary information to propose proper sound level to be offered by the system. The results of the study are as follows; 1) It was considered that the ambience of the center road was dependent upon produced sounds by the system and water sounds of the fountain and that of walk way was mostly dependent upon produced sounds. 2) The results of the subjective evaluation showed that the distance from sound resources was suggestive; the more distant from produced sounds the less full and clear the sounds, the less distant from the sounds of water the more delight and idyllic ambience, and the less distant from the forest the more idyllic ambient and diversity. 3) The results upwards were telling that an average value of six elements for the evaluation was even at the place set back 10.2m from center road and walk way. And harmony of all sounds of the place should be considered to propose suitable sound level of SAFRS.

• The Journal of the Acoustical Society of Korea
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• v.37 no.1
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• pp.1-11
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• 2018

Sound propagation in shallow water changes from spherical spreading to cylindrical spreading, depending on boundary conditions, and this point is defined as a transition point of the sound propagation condition. Theoretically, the transition point can be estimated using the transmission loss as a function of source-receiver range. In this paper, the transmission loss curve in a Pekeris waveguide is predicted using a parabolic-equation based acoustic propagation model and using this transmission loss curve, the range from the source of the transition point is estimated, which is compared to the critical distance calculated using the sound speed ratio of water to sediment. In addition, the effects of the sound speed profile and source depth change on the transition point are investigated. Finally, the transition point is estimated using the transmission loss data measured during the period of the SAVEX15 (Shallow Water Acoustic Variability EXperiment 2015) conducted 65 km southwest of Jeju Island in May 2015, and it is compared to the ocean environmental parameters to understand the properties of sound propagation in the experimental area.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.6 s.123
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• pp.547-552
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• 2007

SAFRS(spontaneous acoustic field reproduction system) is a system to sense changes of surroundings and produce sounds which can go well with environment elements sensed by the system in to the space. The sounds were judged by individual evaluation and, the classification of the preferred sounds according to the mood of the space was suggested in the former study. Effectiveness of SAFRS with field application was validated by prior studies which dealt with researching acoustic environment, evaluating images of sounds, and rating environment with existence and nonexistence of sound resources such as fountains and the system after applied in D university. In this study, for more effective field application of SAFRS, research for the acoustic environment around sound resources and subjective evaluation of the preference of the sounds from the resources were made and it was considered that the results of the experiments should be primary information to propose proper sound level to be offered by the system. The results of the study are as follows; 1) It was considered that the ambience of the center road was dependent upon produced sounds by the system and water sounds of the fountain and that of walk way was mostly dependent upon produced sounds. 2) The results of the subjective evaluation showed that the distance from sound resources was suggestive; the more distant from produced sounds the less full and clear the sounds, the less distant from the sounds of water the more delight and idyllic ambience, and the less distant from the forest the more idyllic ambient and diversity. 3) The results upwards were telling that an average value of six elements for the evaluation was even at the place set back 10.2m from center road and walk way. And harmony of all sounds of the place should be considered to propose suitable sound level of SAFRS.