• Journal of Advanced Marine Engineering and Technology
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• v.23 no.4
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• pp.473-479
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• 1999

The two-microphone sound-intensity technique has been used for the detection of defects in ra-ally loaded ball bearings. The difference in the sound-intensity levels measured for bearings with no defect and for those with intentionally introduced defects of different sizes n heir elements under various operating conditions of loads and speeds is demonstrated. The results show that of an inner-race or ball defect. It is difficult to detect defects at lower speeds. Sound-pressure measurements were also performed for comparison and it shown that the detectability of defects by sound-intensity measurements is better than that by sound-pressure measurements.

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.06c
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• pp.239-242
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• 1998

A new real time sound field visualization technique is introduced in this study using PIV(Particle Imaging Velocimetry) technique. Small particles of which density is small enough to follow up the air flow are used for sound visualization. When the driving frequency is in the vicinity of the resonance frequency of the simplified 2-dimensional muffler system, an acoustic streaming is shown and of which velocity distribution is obtained through PIV technique. It is experimentally proved that the present technique is able to visualize and quantify the sound field's energy flow.

• Journal of Ocean Engineering and Technology
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• v.33 no.5
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• pp.421-426
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• 2019

The directivity of an underwater sound source should be measured in an acoustically open field such as a calm sea or lake, or an anechoic water tank facility. However, technical difficulties arise when practically implementing this in open fields. Signal processing-based techniques such as a sound intensity method and near-field acoustic holography have been adopted to overcome the problem, but these are inefficient in terms of acquisition and maintenance costs. This study established a simple directivity estimation technique with data acquisition, filtering, and analysis tools. A numerical simulation based on an acoustic radiosity method showed that the technique is practicable for sound source directivity estimation in a diffused reverberant acoustic field like a reverberant water tank.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.9
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• pp.695-705
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• 2014

In this paper, two types of techniques for the prediction of radiated sound pressure due to vibration of a structure are investigated. The prediction performance using wave-number sensing technique is compared to that of conventional prediction method, such as Rayleigh's integral method, for the prediction of far-field radiated sound pressure. For a coupled plate, wave-number components are predicted by the vibration response of plate and the prediction performance of far-field sound is verified. In addition, the applicability of distributed sensors that are not allowable to Rayleigh's integral method is considered and these can replace point sensors. Experimental implementation verified the prediction accuracy of far-field sound radiation by the wave-number sensing technique. Prediction results from the technique are as good as those of Rayleigh's integral method and with distributed sensors, more reduced computation time is expected. To predict the radiated sound by the efficient configuration of structural sensors, composed(synthesized) mode considering sound power contribution is determined and from this size and location of sensors are chosen. Four types of sensor configuration are suggested, simulated and compared.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.2 no.2
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• pp.241-248
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• 1998

The accurate measurement of the room sound level is required in environment noise control. However, it has been found that the measurement system noise always corrupts the actual noise from the sound source. In this study, a new sound level measurement technique in which the system noise is eliminated from the measured signal by the cross spectrum method, is proposed. The received signals of two measuring microphones are recorded to DAT through the pre-amplifier and digitized by A/D converter. The cross spectrum calculated from the digitized signals gives the accurate sound level since the system noise is uncorrelated with the sound source noise which we want to measure. The performance of the proposed technique is verified experimentally to be effective and the technique is found to be economic since the low cost general purpose microphone could be used in this technique.

• The Journal of the Acoustical Society of Korea
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• v.15 no.4E
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• pp.3-8
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• 1996

The bubble size distribution is critical information to understand sound propagation and ambient noise in the ocean. To estimate the bubble size distribution in a bubbly water, the sound attenuation has been only in the conventional acoustic bubble sizing method without considering the sound speed variation. However, the effect of the sound speed variation in bubbly water cannot be neglected because of its compressibility variation. The sound attenuation is also affected by the sound speed variation. In this paper, a coherent acoustic bubble sizing inverse technique is introduced as a new bubble sizing technique with considering sound speed variation as well as the sound attenuation. This coherent sizing method is theoretically verified with the bubble distribution functions of single-size, Gaussian, and power-law functions. Its numerical test results with the coherent acoustic bubble sizing method show good agreement with the given bubble distributions.

• International journal of advanced smart convergence
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• v.9 no.4
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• pp.86-95
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• 2020

There is a unique method of musical expression in the nature documentary. The expression method is Mickey Mousing technique, which expresses the movement of animals with music. The Mickey mousing technique can also be used in other types of documentaries, but it is most prominently used in nature documentaries. The Mickey Mousing technique cannot be used in any field other than music composition, because the composer should describe the movement of animals by playing music to match the animal's movements exactly. It is also because they have to play the instrument separately according to the sound source. In this study, we examined the nature documentaries broadcast by KBS over the last five years and analyzed the cases of Mickey Mousing technique. Therefore, we obtained research results that the Mickey Mousing technique is necessary and that the music composition is also necessary as a background music of nature documentaries.

• Journal of Biomedical Engineering Research
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• v.30 no.3
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• pp.233-240
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• 2009

Using a spatial compound imaging technique in a medical ultrasound imaging system, the average speed of sound in a medium of interest is measured, and imaging of its distribution is implemented. When the brightness reaches the highest level in an ultrasonic image obtained as the speed of sound used in focusing is varied, it turns out that the focusing has been accomplished satisfactorily and that the speed of sound which has been adopted becomes the sought-after average speed of sound. Because spatial compound imaging provides many different views of the same object, the adverse effect of erroneous speed-of-sound estimation tends to be more severe in compound imaging than in plain B-mode imaging. Thus, in compound imaging, the average speed of sound even in the case of speckled images can be accurately estimated by observing the brightness change due to different speeds of sound employed. Using this new method that offers spatial diversity, we can construct an image of the speed of sound distribution in a phantom embedded with a 10-mm diameter plastic cylinder whose speed of sound is different from that of the background. The speed of sound in the cylinder is found to be different from that of the surrounding medium.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.3
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• pp.212-219
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• 2011

In this paper, intrusion detection technique based on the sound field variation of audio frequency in the security space is proposed. The sound field formed by sound source can be detected with the microphone when the obstacle or intruder is positioned. The sound field variation due to the intruder is mainly caused by the interference of audio wave. With the help of numerical simulation of sound field formations, the increase or decrease of sound pressure level is analyzed not only by the obstacle, but also by the intruder. Even the microphone is positioned behind the source, sound pressure level can be increased or decreased due to the interference of sound wave. Frequency response test is performed with Gaussian white noise signal to get the whole frequency response from 0 to half of sampling frequency. There are three security cases. Case 1 is the situation of empty space with and without intruder, case 2 is the situation of blocking obstacle with and without intruder, and case 3 is the situation of side blocking obstacle with and without intruder. At each case, the frequency response is obtained first at the security space without intruder, and second with intruder. From the experiment, intruder size of diameter of 50 cm pillar can be successfully detected with the proposed technique. Moreover, the case 2 and case 3 bring about bigger sound field variation. It means that the proposed technique have the potential of more credible security guarantee in real situation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.10a
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• pp.187-192
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• 2010

In this paper, intrusion detection technique based on the sound field variation of audio frequency in the security space is proposed. The sound field formed by sound source can be detected with the microphone when the obstacle or intruder is positioned. The sound field variation due to the intruder is based on the interference of audio wave. With the help of numerical simulation of sound field formations, the increase or decrease of sound pressure level is analyzed not only the obstacle, but also the intruder. Even the microphone is positioned behind the source, sound pressure level can be increase or decrease due to the interference. Frequency response test is performed with Gaussian white noise signal to get the whole frequency response from 0 to half of sampling frequency. There are three security cases. Case 1 is the situation of empty space with and without intruder, case 2 is the situation of blocking obstacle with and without intruder, and case 3 is the situation of side blocking obstacle with and without intruder. At each case, the frequency response is obtained first at the security space without intruder, and second with intruder. From the experiment, intruder size of $50cm{\times}50cm$ can be successfully detected with the proposed technique. Moreover, the case 2 or case 3 bring about bigger sound field variation. It means that the proposed technique have the potential of more credible security sensing in real situation.