• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.05a
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• pp.760-761
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• 2010

As is widely known, SPL measurement using sound level meter (SLM) is limited to higher than 30 dBA, because of the self-noise n(x) of condenser microphone (CM). The authors confirmed n(x) is composed of 3 kinds, each of which is stable enough under the condition -20 ~ +50 deg C to eliminate the influence of n(x) by subtracting its energy from the squared input signal in the integration process, as well as to develop new type of SLM with ultra-low SPL measuring function. This is so-called "0-dB SLM" since it enables to measure SPL down to around 0 dB-SPL. The RMS of n(x) is acquired and stored in ROM in advance, by placing CM in the supersilent space or by using dummy microphone with equivalent capacitance before the actual measurements.

• Journal of Engineering Education Research
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• v.16 no.4
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• pp.21-29
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• 2013

Accreditation of engineering education as initiated by Accreditation Board for Engineering Education of Korea (ABEEK) centers around three key issues: program outcomes, assessment/evaluation thereof, and continuous quality improvement (CQI). Most engineering departments, however, are neither adequately familiar with nor well prepared for the issues, especially CQI. The CQI in almost all departments seems to be overly confined in individual courses and the final capstone design courses for seniors; there is no evidence that CQI is not limited to the course level but flows through all courses in the curriculum. This paper presents a sound and viable framework for CQI implementation in which course-level CQI is integrated into the department/program-level CQI.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.1206-1212
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• 2003

Shell vibrations of the rotary compressor, which account for considerable portion of the noise from compressor, are caused by various sources. Among them is the vibration of the in nor part or cylinder assembly, which undergoes severe compression process and rotational motion. But little researches have been carried out about the behavior and effect of the inner part because of its structural complexity. Furthermore, the shell of the rotary compressor is hermetic type that experimental approach is very difficult. This research studied the structure-born noise of the Rotary compressor using FE an analysis. The comparison between sound pressure spectrum and natural frequencies of the shell vibration implies that shell vibrations contribute significantly to the noise. It is found that inner part vibrations are responsible for those through the FE analysis. Design modification of the inner part, which shifts the target frequencies, reduced overall noise level of the compressor.

• KIPS Transactions on Software and Data Engineering
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• v.3 no.2
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• pp.81-86
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• 2014

In this paper, we present an effective sound classification system for recognizing the real-time context of a smartphone user. Our system avoids unnecessary consumption of limited computational resource by filtering both silence and white noise out of input sound data in the pre-processing step. It also improves the classification performance on low energy-level sounds by amplifying them as pre-processing. Moreover, for efficient learning and application of HMM classification models, our system executes the dimension reduction and discretization on the feature vectors through k-means clustering. We collected a large amount of 8 different type sound data from daily life in a university research building and then conducted experiments using them. Through these experiments, our system showed high classification performance.

• Journal of Biomedical Engineering Research
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• v.19 no.6
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• pp.623-629
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• 1998

To provide sufficient sound to the hearing-impaired person(HIP) who have many difficulty in communication with others using general telephone, big amplification is needed. But big amplification can occur howling as a side effect. In this study we developed the new technique of big amplification without howling, manufactured and estimated the new hearing aid telephone. Telephone speech is divided to three frequency band, amplified respectively and fitted to HIP's hearing ability. The telephone speech frequency is monitored by counter in time domain. The counter transfers the sinusoidal sound to rectangular wave using comparator and counts the number of rectangular wave in a certain time period, that is frequency, to monitor the howling. Telephone have microphone and speaker, which are fitted in a rigid structure and frequency band of telephone sound is limited, so howling occurs in the limited frequency band. If the counter notices that howling conditions happen, microprocessor decreases quickly the gain of the related frequency band. The result of test of our new hearing aid telephone showed that we can amplifiy the sound as much as 40dB, which is meaningful level to many HIP, and make HIP increase their perception ability from 20% to 60.8% in 1 syllable test and from 28.9% to 78% in 2 syllable test.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1243-1246
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• 2006

As remodeling market is growing and peoples' concern on health and well-being is getting high, there is a need to apply environmentally friendly approach to remodeling an apartment houses. But, in point of the impact noise concerned, the thickness of the concrete slab and the limited ceiling height of the remodelling houses are the main constraints to improve the impact noise performance. In order to investigate the effect of the impact noise isolation as structural treatments for the structural elements, heavy-weight impact noise and tapping noise were measured in an remodeling building. As a result, structural strengthening method by H-beam was successful to enhance the impact noise level at about 3 or 4 class by the sound classification system.

• Proceedings of the Korean Society of Computer Information Conference
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• 2014.01a
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• pp.425-426
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• 2014

충격소음(Impulse Noise) 측정 시 지그(Ear Simulator)가 자체적으로 음압측정에 미치는 영향을 확인하기 위해 지그를 이용하여 실내에서 충격소음을 측정하였다. 측정의 신뢰성과 정확성을 확보하기 위해 마이크로폰과 지그에서 동일조건에서 동시에 데이터를 수집하였다. 추가로 헤드&토르소에서 실험을 실시하였다. 최대음압레벨과 1/3옥타브 밴드 결과를 비교분석함으로써 측정 방법에 따른 차이점을 발견하였다.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.10
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• pp.1007-1014
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• 2004

This paper presents a study of low frequencies volume velocity vibration control of a smart panel in order to reduce sound transmission. A distributed piezoelectric quadratically shaped polyvinylidene fluoride (PVDF) polymer film is used as a uniform force actuator and an array of $4\;{\times}\;4$ accelerometer is used as a volume velocity sensor for the implementation of a single-input single-output control system. The theoretical and experimental study of sensor-.actuator frequency response function shows that this sensor-actuator arrangement provides a required strictly positive real frequency response function below about 900 Hz. Direct velocity feedback could therefore be implemented with a limited gain which gives reductions of about 15 dB in vibration level and about 8 dB in acoustic power level at the (1,1) mode of the smart panel. It has been also shown that the shaping error of PVDF actuator could limit the stability and performance of the control system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.368-373
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• 2003

This paper presents a study of low frequencies volume velocity vibration control of a smart panel in order to reduce sound transmission. A distributed piezoelectric quadratically shaped polyvinylidene fluoride (PVDF) polymer film is used as a uniform force actuator and an array of 4$\times$4 accelerometer is used as a volume velocity sensor for the implementation of a single-input single-output con rot system. The theoretical and experimental study of sensor-actuator frequency response function sho vs that this sensor-actuator arrangement provides a required strictly positive real frequency response function below about 900Hz. Direct velocity feedback could therefore be implemented with a limited gain which gives reductions of about 15㏈ in vibration level and about 8 ㏈ in acoustic power level at the (1, 1) mode of the smart Panel. It has been also shown that the shaping error of PVDF actuator could limit he stability and performance of the control system.

• Convergence Security Journal
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• v.6 no.4
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• pp.21-27
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• 2006

With the introduction of sound source sharing over the high speed internet and portable digital audio, the digitalization of sound source has been rapidly expanded and the sales and distribution of sound sources of the former offline markets are stagnant. Also, the problem of infringement of copyright is being issued seriously through illegal reproduction and distribution of digitalized sound sources. To solve these problems, the DRM technology for protecting contents and copyrights in portable digital audio device began to be introduced. However, since the existing DRM was designed based on the fast processing CPU and network environment, there were many problems in directly applying to the devices with small screen resolution, low processing speed and network function such as digital portable audio devices which the contents are downloadable through the PC. In this study, the DRM structural model which maintains similar security level as PC environment in the limited hardware conditions such as portable digital audio devices is proposed and analyzed. The proposed model chose portable digital audio exclusive device as a target platform which showed much better result in the aspect of security and usability compared to the DRM structure of exiting portable digital audio device.