• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.7 s.112
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• pp.683-689
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• 2006

The sound absorption materials have been used to enhance the performance of a noise barrier and improve the room acoustics. In this study, 6 products of sound absorption materials generally used in Korea were chosen, and their absorption performance was tested in various conditions, that is, it was measured while changing thickness, density and air-gap in their back, and measured with or without facing on their face.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.594-599
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• 2000

Two basic acoustic quantities, the characteristic impedances and the propagation constants, of the two different ultra lightweight concrete absorbers were examined with impedance tube method. A transmission loss was tested and compared with theoretical values. The results show that these kinds of sample have proper sound absorption and transmission loss capabilities. It means that they can be used in various fields where noise proof is needed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.885-891
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• 2003

Effects of each acoustic property on absorption characteristics of polyester fiber materials has been studied in this paper. It would be impossible for us to measure effects of each acoustic property by experimental method since we cannot make sound-absorbing materials in which only one of the properties is changed. We have adopted a numerical prediction method to carry out parameter studies for each acoustic property. And to get a general behavior of acoustic performance of the materials, the numerical simulation has been repeated to several cases of different bulk density. Finally we have obtained frequency-dependent control factors in the absorption performance which gives us design capability of acoustic absorbing materials.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.3
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• pp.128-132
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• 2008

The noise levels and individual employee noise exposure levels within a factory will determine the need for hearing conservation program. The difficulty in not having an effective hearing conservation program is the risk of hearing loss that employees may sustain. In the last few years the claims for hearing loss compensation have grown due to class action litigation brought against the employer and companies that have equipment in the factory alleged to have caused hearing loss. The Blower in the factory generates the noise of 98.3dB(A) in the frequency range of 2,000Hz, which may cause occupational hearing loss. By designing close type enclosures which are made of absorption material, about 24.4dB(A) reduction has been in the factory. It is demonstrated that this kind of enclosures can be effectively used to reduce the noise in the factory.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.874-878
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• 2003

Acoustic materials are used for the purpose of absorbing noise and reducing transmission of sound into the receiving room. The purpose of this research is to predict the performance of absorbent materials with respect to absorbing behavior and transmission loss as possible as accurately. The performance of the absorbent materials are carried out systematically as follows: The Biot parameter are measured, first. Then using above parameters as input, LMS's SYSNOISE and VIOLINS programs are used to predict absorption coefficient and transmission loss values, which magnitudes are compared with experimental results. As an sample acoustic material, SK SKY VIVA and PET are selected.

• Journal of KSNVE
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• v.7 no.5
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• pp.781-787
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• 1997

A new method is presented to determine two fundamental acoustic quantities of sound-absorbing materials such as characteristic impedance and propagation constant. In this study, the surface acoustic impedances of sound-absorbing materials are measured using the impedance tube and the anechoic chamber to determine the above acoustic quantities. The measured results are given for two typical sound-absorbing materials(glass wool and urethane foam) int the frequency range between 150 and 1, 600 Hz. The results are verified by other two known methods, which are Smith & Parrott method and Utsuno et al. method. The absorption coefficients calculated from the empirical models(Miki model for glass wool and Jung model for urethane foam) and two quantities by present method are in good agreement with the measured values.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.5 s.98
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• pp.571-577
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• 2005

The acoustic absorption of multiple layer perforated panel systems is largely reduced at the anti-resonance frequency. In order to improve the acoustic absorption at the anti-resonance frequency, the sound absorbing materials are inserted between perforated panels. By the insertion of absorbing materials, it is found that the multiple layer perforated panel system has better acoustic absorption at the anti-resonance frequency and more broadband frequency. Besides, it is shown that the absorption coefficients from the transfer matrix method agree well with the values measured by the two-microphone impedance tube method for various combinations of perforated panels, airspaces or sound absorbing materials.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.6
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• pp.628-633
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• 2009

The helmholtz resonator with the perforated neck has demerits that the absorption performance is not so outstanding in an anti-resonance frequency and high frequency bandwidth. In order to overcome these problems, in the paper, a resonator combined with porous material is proposed. The absorption performances of resonators are measured by two-microphone method and estimated by transfer matrix method. The experimentally measured values of normal absorption coefficients agree well with the corresponding values from the transfer matrix method. Because of the porous material, it is shown that the absorption performance have been significantly improved in the anti-resonance frequency and high frequency bandwidth.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.393-396
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• 2003

Conventional method for designing and installing anechoic chambers is to utilize porous wedges for the sound absorbers. As cutoff frequency lowers down such as 63Hz or 50Hz, the corresponding long wedges diminish the free field area of the chamber. In this study, a new broadband compact absorber(BCA) is introduced which absorbs acoustic energy down to 50Hz. Most prominent is that it measures only 250mm thick. A freely vibrating panel between the non-fibrous absorbers allows tuned absorption at the low frequency region in addition to the high frequency absorption resulted from the conventional absorber installed at the front. Standing waves at low frequency range are suppressed as the BCA modules which are tuned to the corresponding modes absorb sound energy effectively, resulting in anechoic condition. Not only the low frequency performances, but the high frequency absorption is measured to meet adequate conditions for the anechoic chamber. Realized BCA chambers are presented.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.575-580
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• 2013

This study focused on the identification of sound characteristics according to the configuration of sound absorption material and perforated panel dimensions. Noise barriers consist of front perforated panel, sound absorption material and back plate. Noise barriers' acoustic performance should be required to meet the NRC of 0.7. The absorbing performance of the noise barrier relies on the opening ratio of perforated panel and the efficiency of the absorbing material. This study try to find out the possibilities of applications to railway usage.