• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.324-329
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• 2003

An air-conditioner has various noise sources such as cooling fan noise, pumping noise, flow noise and impact noise. Among these, impact noise is the most unpleasant source. This is because the noise is produced in indoor unit of air-conditioner. To control the noise source effectively, first we must identify the noise sources. When we identify impact noise source, the measurement have to be carried out simultaneously. So we use beamforming method that requires less measurement points than intensity method and acoustic holography. The objective of this paper is to estimate the location of impact source. This objective can be achieved by using minimum variance cepstrum that is able to detect impulse embedded in noise. In this study, modified beamforming method based on cepstrum domain is proposed. Then this method applied to air-conditioner noise sources which produce impact noise.

• 한국소음진동공학회논문집
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• 제16권8호
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• pp.789-796
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• 2006

The characteristics of the four standard floor impact sources (impact ball, bang machine, tapping machine, modified tapping machine) and a human impact source (jumping children) were investigated. First, the mechanical impedance of each source were evaluated. Then, the impact force exposure level of each source were measured. The results showed that fundamental frequency and impedance produced by the impact ball are the most similar to those of the human impact source. The frequency characteristics of the impact ball were most similar to those of jumping children. Consequently, the impact ball more accurately reproduces human impact compared to the other standard impact sources. Therefore, the impact ball should be considered as the reliable impactor in evaluating floor impact noise.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.598-603
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• 2002

The floor impact noise in apartment buildings has been known as the most sensitively recognized environmental noise. Therefore. inhabitants perceptual evaluation of floor impact noises was investigated by a questionnaire survey. It was found that the respondents perceive the floor impact noises from the upper nor as a constant noise level. However, if there is any child on the upper floor. the respondents felt Its noise as a harshly grating level. It was also found that the larger the respondents house is. the higher their wanted level of noise isolation is. Moreover, it was revealed that the main source of the floor impact noise from the upper floor is a child at the age from six to seven. The results could be used as fundamental data for the research on impact sources and new regulations that fit to Korean perceptual aspects and characteristics.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.804-807
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• 2005

The characteristics of the standard floor impact sources and the human impact source were investigated. First, the mechanical impedance of the each source was evaluated. Second, the impact force exposure levels and impact sounds level driven by the each source were measured. The results showed that the mechanical impedance and impact force exposure level of the impact ball are the most similar to those of the human impact source among the standard impact sources.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.1075-1075
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• 2006

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.774-779
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• 2004

This paper addresses the way in which we can find where impact noise sources are. Specifically, we have an interest in the case that the signal is embedded in noise. We propose a signal processing method that can identify impulsive sources’location. The method is robust with respect to noise; spatially distributed noise. This has been achieved by a beamforming method with regard to cepstrum domain is used. It is noteworthy that the cepstrum has the ability to detect periodic pulse signal in noise. Numerical simulation and experiments are performed to verify the method. Results show that the proposed technique is quite powerful for localizing the faults in noisy environments. The method also required less microphones than conventional beamforming method.

• 한국음향학회지
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• 제42권6호
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• pp.584-593
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• 2023

본 연구는 실제 생활시 주거 건물에서 발생하는 바닥충격음과 유사한 반복적인 충격원을 개발하려 시도하고, 이렇게 개발되는 새로운 충격원에 대응하는 평가 방법을 찾기 위해 수행되었다. 새로운 충격원을 개발해야 하는 필요성은 실제 주거 건물에서의 바닥충격음과 관련된 문제가 주로 어린이의 뛰는 소리에서 비롯되기 때문이다. 그러나 바닥충격음을 측정하고 평가하는 데 사용된 표준 충격원은 단일 충격 형태로, 실제 생활에서 문제가 되는 충격원과는 다른 특성을 가진다. 연구를 위해 18개의 평가 항목을 도출하였으며, 항목에 대한 설문조사 및 청취실험을 통해 바닥충격음을 평가하는 데 적용 가능한 항목으로 심리적 영향(신경쓰임, 화가 남), 일상 생활 방해(수면 방해, 휴식 방해) 및 생리적 영향(혈압 상승) 항목을 제시하였다. 이들 항목은 개별적으로 활용될 수 있으며, 바닥충격음 평가의 유형에 따라 선택적으로 활용할 수도 있다. 이를 통해 실험실에서 청취 실험의 포괄적인 평가나 바닥충격음과 관련된 주거 환경에서의 소음 평가를 더 체계적으로 수행할 수 있을 것이다.

• 한국정밀공학회지
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• 제19권3호
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• pp.144-151
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• 2002

This work focuses on finding out the noise source and the method of reducing the noise level of LPG(liquefied petroleum gas) fuel injector. The noise of LPG injector in operating condition is due to the impact between valve and valve seat. This study shows that if the revolution of engine is increased, the noise of LPG injector will be more serious but it is not nearly affected by the increment of fuel pressure. The source and transmission paths of noise are identified through the analysis of noise generation mechanism and noise spectrum. The sound absorbing material is tested to verify its efficiency of sound absorption thor the LPG injector. The effect of noise reduction of absorbing material is remarkable when the engine speed is high. Consequently two methods of reducing the noise level are suggested from the identified results. The one is to equip the absorbing material on the outer side of injector and the other is to coat with a soft material or equip a soft ring on the surface of impact.

• 한국소음진동공학회논문집
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• 제24권6호
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• pp.483-492
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• 2014

Uncomfortable feelings of occupants by indoor floor impact noise in a residential building are not accurately represented by the floor impact noise from a standard impact source. It is due to the characteristics of standard impact sources, which are different from the impact forces produced by occupants. It varies significantly by impact source, and it is not easy to be replicated for testing. As a result, the indoor floor impact noise under different acoustic conditions cannot be directly compared. Using frequency response function(FRF), which represents the input-output relationships of a dynamic system, it is possible to examine the characteristics of the system. Especially, FRF can predict the response of a linear dynamic system subjected to various excitation. To determine the relationship between impact force and the corresponding response of dynamic system in residential building, the acceleration response of a concrete slab and the floor impact noise in the living room, produced by bang-machine and rubber-ball excitation, were measured. The test results are compared to the estimates based on FRF and impact force spectrum.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.463-468
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• 2007

The abnormal sound of generator frame is analyzed by a acceleration signal. The spike-like time signal is major characteristics of impacting force. The distributional map of vibration level is one of visualization method. With map, noise source was easily detected. After de_assembly of generator, loose part of internal component is the source of impact force by mechanical movement of stator inherently. In contact condition of part with clearance, the level of impact signal is different at each revolution and impact signal did not happens periodically.