• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.681-686
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• 1997

Foamed aluminum is well known metallic porous sound absorption material which has excellent properties of light weight and high absorbing performance. For the purpose of finding out the sound field characteristics within a simple closed cubic enclosure with foamed aluminum, analytic and experimental studies are performed. For the first time, the standing wave apparatus is used to measure absorption coefficient and impedance of the foamed aluminum. Next, the sound effects of absorption material in acoustically loaded rectangular enclosure are identified according as the foamed aluminim is to be or not.

• Journal of KSNVE
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• v.7 no.3
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• pp.457-466
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• 1997

The experimental and analytical study was conducted to determine the noise transmission characteristics of acoustically loaded steel plate of rectangular enclosure and to investigate the sound radiation characteristics through out the enclosure. The vibrations of acoustically loaded plate give rise to sound radiations and generate the reverberant space that the sound field exists very close to a vibrating plate. Acoustic transmission loss is measured from the incident intensity into the plate and the transmitted intensity through out the plate. Sound radiation patterns are measured from both acoustic intensity technique and surface intensity technique. Those resultant patterns and vibrational modes are vital in understanding the relations between vibration and noise in the near field out of vibrating plate.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.87-88
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• 2007

An acoustic total or partial enclosure is widely used to reduce the sound pressure level propagating from a noise source. However, the performance of the acoustic enclosure is decreased by its inherent limitations such as temperature rise or acoustic pressure build-up inside the enclosed acoustic field. In this reason, an acoustic enclosure consisting of a silencer and absobent panels with acoustic resonators is studied to reduce the transmitted noise from a transformer. Large sound-attenuation is expected by applying the enclosure to the large transformers in a substation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.581-586
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• 2000

The equivalent source method is used to calculate the internal pressure field for an enclosure which can have arbitrary boundary conditions and may include internal objects which scatter the sound. Some of the equivalent positions are chosen to be the same as the first order images of the source inside the enclosure, some are positioned on a spherical surface some distance outside the enclosure. The normal velocity on the surfaces of the enclosure walls is evaluated at a larger number of positions than there are equivalent sources. The sum of the squared difference between this velocity and the expected is minimized by adjusting the strength of the equivalent sources. The convergence of this method is checked by evaluating the velocity error at a larger number of monitoring positions. Example results are presented for various numbers of sources and evaluation points. The results showed that in general the more equivalent sources increased the accuracy of the sound field predictions but the accuracy is not too much sensitive to the numbers of evaluation points.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.10
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• pp.107-114
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• 2009

Because of the increase of power demand and expansion of downtown, it is necessary to install the power transformers at the substation in the residential area. But the public complaints have increased due to the noise of the power transformers in the substation. A soundproof wall has been employed to the power transformers in the outdoor substations and a soundproof door, a soundproof shutter and soundproof equipment for wind-path has been employed to power transformers in the indoor substations in order to isolate sound propagation from the noise of the power transformers. But the noise reduction results of these methods are not satisfied. In this study, a soundproof enclosure is developed to effectively isolate sound propagation from the noise of the power transformers. The performance of the sound attenuation of the developed soundproof enclosure is verified in a 154[kV] transformer. As a result, 15[dB] sound attenuation in 120[Hz] component is achieved by applying the developed soundproof enclosure to a 154[kV] transformer.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.1203-1209
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• 2001

Identification of noise sources, their locations and strengths, have been taken great attention. The method that can identify noise sources normally assumes that noise sources are located at a free field. However, the sound in a reverberant field consists of that coming directly from the source plus sound reflected or scattered by the walls or objects in the field. In contrast to the exterior sound field, reflections are added to sound field. Therefore, we have to consider the reverberation effect on the source identification method. The main objective of this paper is to identify noise source in the reverberant field. At fist, we try to identify noise sources in a rigid wall enclosure using the spherical beamforming method. In many case of practical interest, the wall has an admittance so that complex reflection process occurred. In this paper, we assumed the complex reverberant field in the enclosure to be the sum of plane waves with random incidence and magnitude. Then the effects of reverberant field at interior source identification have been studied theoretically as well as experimentally

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.7
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• pp.520-526
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• 2002

Identification of noose sources, their locations and strengths, has been taken great attention. The methods that can identify noise sources normally assume that noise sources are located in a free field. However, the sound in a reverberant field consists of that coming directly from the source plus sound reflected or scattered by the walls or objects in the field. In contrast to the exterior sound field. reflections are added to sound field. Therefore, we haute to consider the reverberation effect on the source identification method. The main objective of this paper is to identify noise source in the reverberant field. At fist, we try to identify noise sources in a rigid wall emc;psire using the beamforming method. In many cases of practical interest, the wall has admittance so that random reflections occur in an enclosure. In this paper, we assumed the complex reverberant field in the enclosure to be the sum of plane caves with random Incidence and magnitude. Then we try to explain effects of reverberant field at interior source identification.

• Journal of the Korean Society of Safety
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• v.9 no.4
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• pp.119-124
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• 1994

The considerations in the noise control by enclosure are the rise of temperature and sound pressure, transmission loss, absorption coefficient of the materials, the structure of the soundproof panels, an opening and coincidence frequency. But it is very difficult that we obtain the accurate data about those in design, so, the noise reduction after enclosing does not correspond with the calculation. The difference of the noise reduction between the calculation and the measurement was 8.2dBA, and we can obtain the approximate result as the following formula which correct 10dBA, safely.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.4 s.181
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• pp.60-66
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• 2006

For the purpose of finding out the sound field characteristics in a rectangular cavity, analytical and experimental studies are performed with white noise input. Two-microphone impedance tube method is used to measure the impedances of foamed aluminum. Foamed aluminum is well known metallic porous material which has excellent properties of light weight and high absorbing performance. And predicted impedances of foamed aluminum are compared with measured impedances. The predicted acoustical parameters are applied to the theoretical analysis to predict sound pressure field in the cavity. The measured sound absorption effects are compared with the predicted values for both cases with and without foamed aluminum lining in the cavity of the rectangular enclosure.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.2
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• pp.263-271
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• 2008

Compressor radiated noise is one of the dominant noise for the outdoor unit of the air conditioner. Therefore, air conditioner makers are trying to reduce it continuously. Even though noise absorption and isolation technology are one of the important parts for reducing the noise from the compressor, it is usually treated to the substitute technology when the noise from the compressor is very difficult to reduce by the compressor noise control only. In this paper, we focus on the property of the sound insulation for the cabinet and measure it applying the theory of the sound transmission loss and insertion loss of the simple enclosure. The insertion loss is evaluated by the experiments according to the thickness and the aperture of the partition in the cabinet.