• The Journal of the Acoustical Society of Korea
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• v.31 no.1
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• pp.29-38
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• 2012

This paper presents a transient noise reduction system in a speech signal. The proposed transient noise reduction system utilizes a median filter to reduce the transient noise. Since the median filter can distort speech during the noise reduction, a long-term prediction (LTP) filter is adopted as a pre-processor to minimize speech distortion. The speech information preserved by the LTP filter is re-synthesized after reducing the noise. This paper verifies the weakness of a linear prediction (LP) filter and the superiority of the LTP filter for preserving the speech component in transient noise presence environment. Applying the proposed system, the signal-to-noise ratio (SNR) of output is improved by 8dB in both speech and noise presence region, and PESQ score is increased by 1 point comparing with noisy input.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.9
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• pp.71-77
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• 2020

In recent years, as a consequence of the technological advancements in the automobile industry and changes in consumer demands, the reduction of noise inside vehicles rather than vehicle performance has increasingly become an important factor of interest. To date, most studies have focused on noise and vibration reduction techniques for the engine and drive system of vehicles. In this research, a comparative analysis for reducing the effect of vehicle seatbelts on the transient response is performed using the test of vehicle conditions and transient response analysis in accordance with seatbelt conditions. After the sensitivity analysis, the specifications for improvement were designed based on the transient response analysis. It was confirmed that the transient response characteristics were improved by the transient response analysis and vehicle conditions test. Through computer-aided engineering, the transient response characteristics of seatbelts were checked with less cost and time.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.577-582
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• 2012

Recently, noise reduction of air-conditioner is one of the important design factors for high quality product. Especially, customer complaints arise due to noise problem of the outdoor unit. After the operation of air-conditioner start, noise level of outdoor unit is increased gradually and sometimes abnormal noise occurs until it reaches steady state condition. The aim of this paper is to investigate the relation between noise of outdoor unit and thermodynamic properties of cycle at transient condition of room air-conditioner. In order to find out the noise characteristics of outdoor unit, noise and vibration measurements are carried out. Also, the thermodynamic properties of compressor and heat exchanger are measured by using temperature and pressure sensors and experimental results are discussed. Finally, we find out the relation between noise and cycle properties at starting of room air-conditioner and the improvement method to reduce noise level is proposed.

• Economic and Environmental Geology
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• v.31 no.1
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• pp.53-57
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• 1998

Transient electromagnetic (TEM) method is also affected by cultural and natural electromagnetic (EM) noises, since it uses part of the broadband ($10^{-2}$ to $10^5Hz$) spectrum. Especially, predominant EM noise which affects a moving transmitter-receiver TEM system is sensor motion-induced noise. This noise is caused by the sensor motion in the earth magnetic field. The technique for reducing the sensor motion-induced EM noise presented in this paper is based on Halverson stacking. This Halverson stacking is generally used in a time-domain induced polarisation (IP) system to reject DC offset and linear drift. According to spectrum analysis of the vertical component of sensor motion-induced noise, the frequency range affected by the motion of an EM sensor is less than about 700 Hz in this study. With the decrease of the frequency, the spectral power caused by the motion of a sensor increases. For example, at the frequency of 200 Hz, the spectral power of the sensor motion-induced noise is $-90dBVrms^2$ while the spectral power of the EM noise measured with a fixed sensor on the ground is $-105dBVrms^2$, and at the frequency of 100 Hz, the spectral power of the sensor motion-induced noise is $-70dBVrms^2$ while the spectral power of the EM noise measured with a fixed sensor on the ground is $-105dBVrms^2$. With applying Halverson stacking to an artificial noise transient generated by adding a noise-free transient to sensor motion-induced noise measured without pulsing, it is shown that the filtered transient is nearly consistent with the noise-free transient within a delay time of $0.5{{\mu}sec}$. The inversion obtained from this filtered transient is in accord with the true model with an error of 5%.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.10a
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• pp.185-189
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• 2009

It is very important to control the vibration transmitted from external utilities and the transient response due to the internal sources for the precision equipment, which is very sensitive to the vibration environment. The anti-vibration tables that use air springs have been widely used due to their excellent isolation performance, but the systems with high flexibility have the critical problem of large transient response by the impulsive force of the moving mass in operation of the equipment. In this paper, the hybrid vibration control system is proposed, which is combined the air springs with the semi-active MR dampers in order to satisfy the performances of isolation and vibration reduction simutaneously.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.14 no.6
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• pp.18-25
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• 2000

This paper describes the design and fabrication of a home-panel board for electromagnetic compatibility which can protect home-electric appliances from transient voltages and power line noise. The proposed panel board include a transient voltage blocking device and a EMI filter which consisted of varistors, capacitors, and bus line inductance.A performance test of the prototype panel board, blocking characteristics to transient voltages and reduction characteristics to power line noise, are carried out by using a combination surge generator standardized in IEC and a network analyzer.The results showed that the proposed panel board is satisfied with the surge immunity level of IEC 61000-4-5, and has an over 20[dB] noise reduction performance in ranges from 150[kHz]∼30[MHz].

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.202-207
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• 2006

The aeroacoustic noise from intake head of a vacuum cleaner is caused by complicated transient pressure fluctuation and it greatly affects the overall SPL of the vacuum cleaner. In this study, we intended to decrease the overall SPL by reducing the aeroacoustic noise from intake head. In the first the place, we analyzed the aeroacoustic noise from the unsteady fluid analysis of intake head. And then, we grasped the dominant frequency band from the aeroacoustic noise by comparing the spectrum distributions between examinations and analyses. Also, we systematically investigated the aeroacoustic noise sources from each part composing the intake head. Consequently, we redesigned each part of the dominant noise sources and suggested the modified intake head, resulting in the reduction ortho overall SPL by 3.6dB(A).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.588-592
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• 2002

There was the transient vibration on $H_2$ piping system for cooling the generator in a power plant. We found it was resulted from resonance between the natural vibration of the piping system and exciting force from the turbine rotor by measurement and simulation test. We verified it would be changed the mode shape of the piping system by several simulation test for the structural modification of the piping system. Therefore we concluded that the change of natural vibration mode depends on deeply changing effective length of pipe and reducing supports.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.11a
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• pp.486-489
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• 1999

This paper deals with the design rule and performance results of the transient voltage blocking devices (TBD) for low-voltage mains on shipboard. The proposed TBD consists of metal oxide varistors (MOV) and L-C filter to improve noise-elimination performance. Three kinds of TBDs are fabricated and tested by using a combination surge generator which can produce the standard impulse current of 8/20${\mu}$s 2.1kA. As a reults, the proposed TBD with series L-C filter has more excellent transient blocking and noise reduction performance than the conventional TBDs.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.90-94
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• 2021

With the increased interest on quiescent place for residential place, the noise generation from facilities needs to be minimized. One important noise source include sounds from operation of elevators. The elevator operates between floors and generates significantly annoying sounds to the nearby living spaces. It is recognized as the significant contributor inducing noise annoyance to residents. Elevator is supported to the building structure at several locations for movements between floors. In this study, the vibration reduction by use of polymer concrete on the support location was demonstrated. By measuring and comparing the vibration generation when supported on cement and polymer concrete, the noise reduction performance was evaluated. The polymer concrete was made in the form of being inserted into the wall that imitates the hoistway. The impact vibration was induced to the bracket and vibration transfer magnitude was measured. The damping ratio was evaluated through normalization and curve fitting of transient response, and comparison was performed for each resin mixing ratio. By use of polymer concrete, it was possible to reduce the vibration generation in an effect manner without sacrifice on the structural rigidity.