• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1183-1186
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• 2007

The low frequency noise, including infra-sound is known to affect human physiology and psychology. Guidelines and measurement method of low frequency noise has been introduced in several countries in order to evaluate low frequency noise. In this work, low frequency noise characteristics of dump truck was investigated in terms of the noise level and spectrum. The interior sound pressure level of the dump truck was between 60 and 105 dB in the frequency range of $1{\sim}250$ Hz.

• Journal of Korea Society of Industrial Information Systems
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• v.20 no.1
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• pp.49-55
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• 2015

This paper proposes a 2.4 GHz RF oscillator with a very low close-in phase noise performance. This is composed of a low frequency crystal oscillator and three frequency multipliers such as two doubler (X2) and one tripler (X3). The proposed oscillator is implemented as a hybrid type circuit design using a discrete silicon bipolar transistor. The measurement results of the proposed oscillator structure show -115 dBc/Hz close-in phase noise at 10 kHz offset frequency, while only dissipating 5 mW from a 1-V supply. Its close-in phase noise level is very close to that of a low frequency crystal oscillator with little degradation of noise performance. The proposed structure which is consisted of a low frequency crystal oscillator and a frequency multiplier provides new method to implement a low power low close-in phase noise RF local oscillator.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.11
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• pp.1113-1120
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• 2012

This paper deals with the analysis of interior noise and low frequency noise characteristic for the Busan citizens to use public transport, Busan Metro Line 3. The interior noise evaluation index, articulation index(AI) is evaluated the lower value about average 22 % in a whole range, this is difficult to have a conversation. Also, noise criteria(NC) curve is partially evaluated as NC-65 below 2000 Hz, space type is evaluated as factories. Another of interior noise evaluation index, preferred speech interference level(PSIL) is evaluated the upper value about average 66 dB(A) in a whole range, this is evaluated to be interrupted. In the case of low frequency noise(20~200 Hz), the measurement of low frequency noise is assessed largely beyond noise criteria of ISO 226. The low frequency noise should be reduced because low frequency noise affects on psychological stress and displeasure although low frequency noise is not recognized by auditory sense. The low frequency noise criteria and guideline will be enacted from now on in Korea.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.887-890
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• 2007

The low frequency noise, including infra-sound is known to affect human physiology and psychology. Guidelines and measurement method of low frequency noise has been introduced in several countries in order to evaluate low frequency noise. In this work, low frequency characteristics of Daejeon subway was investigated in terms of the noise level and spectrum in the interior of running subway car and the subway station. The interior sound pressure level of the passenger car was between 60 and 102 dB in the frequency range of $1{\sim}250$ Hz.

• Ocean and Polar Research
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• v.29 no.4
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• pp.311-316
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• 2007

Ocean noise may be used for monitoring wind speed and rainfall rate on the sea surface, as well as for tracking whales' migration routes. In particular, low-frequency ocean noise has recently been of concern with relation to the behavior of marine mammals. Low-frequency ocean noise has been increasing over the past few decades due to increase of ship traffic and offshore oil industry activities. Mechanical noise such as flow noise and cable strumming noise may be induced if low-frequency ocean noise is measured by cabled traditional hydrophone in high current areas. To successfully measure low-frequency ocean noise in a shallow water environment with strong current, we developed a self-recording hydrophone. This paper describes the main configurations of the self-recording hydrophone and presents some results on measured data.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.148-152
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• 1996

A method of deminishing low frequency noise by acoustic acoupling with compliant wall is described. The coupled governing equations and boundary conditions are derived and solved. The coupled system shows very interesting behavior in the low frequency region; in the low frequency, acoustic wave doesn't propagate, but decay to satisfy the boundary condition with the compliant wall. Henceforth using this mechanism, we propose a method of reducing low frequency noise, which is infact related with the physical properties of compliant wall. The method has been experimentally verified.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1482-1489
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• 2007

In this paper, characteristics of infrasound and low-frequency noise emission from large modern wind turbines are experimentally investigated. The sound measurement procedures of IEC 61400-11 and ISO 7196 are utilized to field test and evaluation of noise emission from each of 1.5 MW and 660 kW wind turbines using the stall regulation and the pitch control for the power regulation, respectively. It was found that the G-weighted SPLs of low-frequency noise including infrasound shows positive correlation with the wind speeds, irrespective of methods of power regulation. This highlights the potential complaint of local community against the infrasound and low-frequency noise of wind turbines. The comparison of measured data with the existing hearing thresholds and criteria curves shows that it is highly probable that the low-frequency noise from the 1.5 MW and 660 kW wind turbines in the frequency range over 30 Hz leads to the psychological complaint of ordinary adults, and that the infrasound in the frequency range from 5 Hz to 8 Hz causes the complaint by rattling the house fitting such as doors and windows.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.11
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• pp.957-965
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• 2013

This paper deals with analytical methods for low frequency and high frequency brake squeal noise on brake-rear caliper. In order to improve low frequency and high frequency squeal noise, we take survey caliper bracket shape parameters and housing shape parameters. Besides, using the combination of bracket and housing parameter were surveyed. Thus, using the combination of bracket Alt_05 and housing Alt_45 specifications, instability analysis and brake dynamo test were carried out. Based upon the two models, low and high frequency squeal noise of base model were improved. But, for 6.0 kHz frequency noise, which is not improved, it needs to additionally study on instability analysis and combination of the other brake components.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.384.2-384
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• 2002

Compressor is a major noise source of air-conditioner. Especially, its low frequency band noise below 1000㎐ is very important because it will not be attenuated by passing through the cover panel and heat exchanger in air-conditioner. The factors affecting the low frequency band noise are studied by geometric similarity along with several experiments, and the low frequency noise is closely related with the discharge holes of muffler as well as the cavity of lower shell. (omitted)

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.127-131
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• 2007

A laboratory study on low frequency noise assessment was carried out to determine the acceptability limits in the frequency range between 20 and 200 Hz. The acceptability limits were tested in the anechoic chamber to minimize the background noise. A total of 30 test subjects, who were aged between 19 to 33 years, participated in this study. They were exposed to various stimuli for about 1 hour by supra-aural earphone. The experiment consisted of two listening sessions; hearing threshold and the acceptability limits session. The results showed that the trend of the acceptability limits curve was approximately equal to C-weighting curve which had been found to be superior to A-weighting curve in low frequency noise assessment.