• 소음진동
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• 제7권1호
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• pp.71-79
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• 1997

The objective of this study is to investigate experimentally the effect of surface conditions of the plate on the impinging jet noise. The experimental results about the spectrum, the sound pressure level and the directivity are pressented and discussed in relation with the surface conditions. Regardless of the surface conditions, the pure tones of high level are generated at the same frequency band and the overall sound power level of impinging jets is much higher than that of the free jet. However, the velocity dependence of the sound pressure level and the directivity are different between smooth surfaces and rough surfaces. The dependence of sound pressure level on the jet velocity shows that the smooth surface generates quadrupole-type sound like free jets. However, the perforated or the rough surface radiates sound power exactly proportional to the sixth power of the jet velocity, indicating that the source is fixed dipole type. The directivities of 1/3 octave band sound pressure level for both the free and impinging jet show the peak directivity at 115$^\circ$ upstream, probably due to the refraction associated with velocity gradient.

• 한국소음진동공학회논문집
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• 제27권1호
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• pp.100-106
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• 2017

Sound quality engineering in automobile noise applications has become more and more important under the current quiet driving condition because various noise components masked under high noise level can be audible in quieter driving situation. Many researches have been carried out for subjective and objective assessments on automobile sounds and noises. In particular, the interior sound quality has been one of research fields that can give high-quality feature to automobile products. Although many works related to the interior sound quality have been progressed or completed in foreign countries, limited research results are presented in the country. In the study, subjective assessments are first performed with 20 subjects to select perceptual adjectives suitable to the assessment of car interior noises during acceleration. The selected perceptual adjectives are employed as the assessment scales to evaluate the acceleration noises in questionnaire procedures using 35 subjects, for which several noises are created through digital filtering of the acceleration noises measured. Mean values and standard deviations for subjective assessment scores obtained by the questionnaire procedures are calculated and their reliability are also verified. Finally, various statistical analyses such as the correlation analysis and the factor analysis are carried out to reveal the interrelationship between the assessment scales and the spectrum components of the acceleration noises.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 학술회의 논문집 정보 및 제어부문 B
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• pp.878-881
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• 2003

To acquire an appointed speaker's clear voice signal from inspect-camera, picture-conference or hands free microphone eliminating interference noises needs to be preceded speaker's position automatically. Presumption of sound source position's basic algorithm is about measuring TDOA(Time Difference Of Arrival) from reaching same signals between two microphones. This main project uses ADF(Adaptive Delay Filter) [4] and CPS(Cross Power Spectrum) [5] which are one of the most important analysis of TDOA. From these analysis this project proposes presumption of real time sound source position and improved model NI-ADF which makes possible to presume both directions of sound source position. NI-ADF noticed that if auditory sense of humankind reaches above to some specified level in specified frequency, it will accept sound through activated nerve. NI-ADF also proposes practicable algorithm, the presumption of real time sound source position including both directions, that when microphone loads to some specified system, it will use sounds level difference from external system related to sounds of diffraction phenomenon. In accordance with the project, when existing both direction adaptation filter's algorithm measures sound source, it increases more than twice number by measuring one way. Preserving this weak point, this project proposes improved algorithm to presume real time in both directions.

• 스마트미디어저널
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• 제11권1호
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• pp.31-37
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• 2022

본 논문은 일상생활에서 흔히 들을 수 있는 소리(비명소리, 박수 소리, 여러 명의 박수 소리, 자동차 지나가는 소리, 배경음 등)를 감지하는 음향 인식을 위하여, 신호처리 및 딥러닝을 적용하는 연구에 관한 것이다. 제안된 음향 인식에서는, 인식 정확도의 향상을 위해서 음향 파형의 스펙트럼, 음향 데이터의 증강, 2차원(2-D) 이미지 변환에 관한 기술들이 사용되었고, 예측의 정확도를 향상을 위한 앙상블 학습, Convolution Neural Network(CNN) 딥러닝 기술들이 적용된다. 제안된 음향 인식 기술은 실험을 통해 다양한 음향을 정확하게 인식할 수 있음을 보여준다.

• 한국수산과학회지
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• 제34권2호
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• pp.151-155
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• 2001

해양 목장에서 음향 순치 대상 어종으로 사용할 수 있는 볼락의 청각 문턱치를 기본으로 하여 음향 어법의 기초 자료를 제공할 목적으로 볼락의 백색 잡음에 대한 청각 임계비와 학습 및 유집을 위한 방성 음압 강도를 조사한 결과는 다음과 같다. 음압 73, 78, 83dB의 3단계 백색 잡음을 방성하였을 때 볼락의 청각 문턱치는 백색 잡음이 없을 때보다 높게 나타나 마스킹 현상이 나타났고, 주파수 300Hz에서 보다 높게 나타났다. 볼락의 청각 임계비는 측정 주파수 80, 100, 200, 300, 500, 800Hz에서 음압이 대략 28, 34, 26, 30, 47, 52dB이고 마스킹 현상은 주파수 300Hz에서 음압 65dB의 잡음 레벨에서 나타나기 시작하였고 그 외의 주파수에서는 음압 68dB 이상에서 나타났으며, 볼락이 주파수 $200\~300$Hz에서 신호음을 인식하기 위해서는 음압 96dB 이상, 잡음 레벨보다 약 26dB 이상의 높은 음압이 요구되었다.

• 수산해양기술연구
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• 제16권1호
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• pp.1-15
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• 1980

An underwater recording system was designed to measure the sound spectra of the underwater noises produced by fishing gears in operation. Recorded were noi~es from three types of fishing gears: an anchovy set net, three anchovy boat seine net and a stern trawlnet. Acoustic analysis were made using a heterodyne analyzer, a digital frequency analyzer and a level recorder. The no;'e produced by the anchovy set net was found in the high frequency region of the onset of ambient noise spectrum with a slope of - 6 dB/octave. Here the ambient noise spectrum is higher, though similar in shape, than Knudsen spectrum, and is attributed to the breaking action of the coastal wave. Measured noise spectra during the fishing operations of the anchovy boat seine nets are attributed to the background noise of the sea in the presence of the fishing vessels. The frequency distribution of the noise was 20~5, 000 Hz in the case of two steel anchovy boat seiners, and 20-3,000 Hz in the case of the wooden anchovy boat seiner. The predominant frequency range was 250~350 Hz and maximum sound pressure level was 122 dB (re $1\muPa$) in the case of the steel boat and ] 17 dB in the case of the wooden boat. The noises produced by the trawl fishing gears are remarkably higher than the background noi~e in the presence of the fishing vessel. The frequency distribution of the noi~e was 20-6,300 Hz. The predominant frequency range was 100~200 Hz and maximum sound pressure level was 137 dB ( re $1\muPa$) . The noise spectra were not so much different from that caused by vibrations of the towing cable and the structure of the ground rope of the trawl net towed in an experimental tank.

• 대한기계학회논문집B
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• 제24권10호
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• pp.1326-1334
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• 2000

The oscillatory excitation with a Strouhal number of 2.65 ncar the stagnation zone of hemispherical nose model was employed to control the laminar separation bubble and the transition to turbulence. The effects of oscillatory excitation upon the separation bubble and the transition were addressed in terms of kurtosis/skewness and time-frequency analyses. The measured noise spectrum of radiated sound from the turbulent boundary layer on the axi-symmetric infinite cylinder is compared with that by Sevik's wave-number white approximations. The noise sources in TBL on axi-symmetric cylinder and the caling of their far-field sound are also discussed.

• Fibers and Polymers
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• 제1권1호
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• pp.59-65
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• 2000

In order to investigate psychoacoustic characteristics of fibers, and to compare them with sound physical parameters, each sound of 25 different fabrics consisted of a single fiber such as wool, cotton, silk, polyester, and nylon was recorded. Sounds of specimens were transformed into critical band diagram and psychoacoustic characteristics including loudness and sharpness for each sound were calculated based on Zwicker＇s models. Physical parameters such as the level pressure of total sound (LPT), level ranges (ΔL), frequency differences (Δf), AR coefficients (ARC, ARF, ARE) were obtained in fast fourier transform (FFT) spectrum. Nylon taffeta showed higher values for loudness than 2.5 sone corresponding to human low conversation, while most silk fibers generated less louder showing lower values for loudness than 1.0 sone. Wool fibers had higher loudness mean value than that of cotton, while the two fibers didn't differ in LPT. Loudness showed high positive correlation coefficients with both LPT and ARC. Sharpness values were higher for wool fiber group than other fibers. Sharpness was not concerned with loudness, LPT, and ARC, but the fabrics with higher values for sharpness tended to show higher ΔL.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.973-978
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• 2001

Noise reduction has become a major issue of the manufacturing industry. This paper describes the reduction of noise and vibration of rotary compressors. Empirical design for the present strap of the accumulator has been considered to be sufficient for the constraint of the accumulator resonance modes without thorough study. Recently, however, some researchers found out that the accumulator contributes considerably to the sound propagation. In this paper, the contribution of accumulator to the noise propagation is investigated through sound measuring experiments by checking the directivity of the noise. And, experimental modal analysis results show that frequencies of some resonance modes of the accumulator coincide with the highest peaks on sound spectrum. To demonstrate the reason for those resonance modes, a finite element analysis is conducted. Normal mode analysis of the finite element model of the rotary compressor shows the mechanism of the accumulator resonance modes.

• International Journal of Air-Conditioning and Refrigeration
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• 제8권2호
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• pp.89-100
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• 2000

Present study explains some experimental results on the aerodynamic noise of the cross-flow fan usually installed in the indoor unit of the room air-conditioners and provides a simple reduction method of radiating sound to decrease the total noise level. The spectra of the noise of the cross-flow fan were analyzed by the spectral decomposition method to characterize the generated sound. The unsteady fluctuating flow field was also measured using the I-type hot-wire probe. Comparing the spectral characteristics of the sound and the flow velocity, a useful noise reduction method was proposed, which bounds the region with a fence where the flow fluctuations were noticeably changed in the same fashion as the source spectral distribution functions vary. To validate the proposed method for reducing noise generated by the cross-flow fan, the sound pressure levels of the cross-flow fan system were compared with and without the bounding fence for various flow rates.