• Journal of Biomedical Engineering Research
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• 제30권3호
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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.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• 제14권1호
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• pp.63-72
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• 2002

The main objective of this study is to propose a practical two-microphone impedance tube method to measure the sound transmission loss for flexible sound isolation sheets without the use of the time-consuming and expensive reverberation room. This method was based on the sound decomposition theory developed by Seybert using the spectral density functions of the incident and reflected sound waves. In order to verify the validity of the experimental results, the measured sound transmission losses from the proposed method were compared with the measured data from the reverberation room method and the calculated data from the theory satisfying the mass law of sound isolation material. The resulted trends of the sound transmission losses versus frequencies for several different sound isolation sheets were almost same for each other and agreed quite well in both methods except at some low frequency region. From the experimental results, it was found that the accuracy of sound isolation capability obtained by two-microphone impedance tube method depends upon the microphone spacing, the distance from the first microphone to the test sample surface and the test sample location.

• Journal of the Korea Computer Graphics Society
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• 제24권5호
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• pp.21-30
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• 2018

In this paper, we use Sound-tracing, a 3D sound technology based on ray-tracing that uses geometric method as auditory technology to enhance realism. The Sound-tracing is costly in the sound propagation stage. In order to reduce the sound propagation cost, we propose a method to calculate the average effective frame number of previous frames using the frame coherence property and to adjust the depth according to the space based on the calculated number. Experimental results show that the path loss rate is 0.72% and the traversal & Intersection test calculation amount is decreased by 85.13% and the frame rate is increased by 4.48% when the sound source is indoors, compared with the result of the case without depth control. When the sound source was outdoors, the path loss was 0% and the traversal & Intersection test calculation amount is decreased by 25.01% and the frame rate increased by 7.85%. This allowed the rendering performance to be increased while minimizing the path loss rate.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 2006년도 추계학술대회논문집
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• pp.498-501
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• 2006

When an object or objects, rigid or flexible, presents in incident sound field, the sound wave is scattered. This, we call, is scattered sound field. It, of course, depends on the amplitude and the direction of the incident sound field as well as the geometry and the surface impedance of the scatterer(object). This paper addresses the way to measure scattered sound field by using arbitrary incident sound wave. This means that the method can decompose the scattered field from measured sound field with respect to any magnitudes and directions of incident plane-waves.

• Interaction and multiscale mechanics
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• 제3권4호
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• pp.373-387
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• 2010

This study is intended to assess low frequency sound radiated from a viaduct under normal traffic. The bridge comprises steel box girders and wide cantilever decks on which vehicles pass. The low frequency sound and the acceleration response of the bridge under normal traffic are measured to investigate how bridge vibrations affect the low frequency sound observed near the bridge. Observations demonstrate that strong relationships exist between frequency characteristic of bridge's acceleration response and the sound pressure level of low frequency sound. A noteworthy point is that the dynamic feature of the sound pressure level is mostly affected by dynamic feature of the span locating near the observation point.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.1138-1141
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• 2002

In this study, the ISO 15186-1 “Measurement of sound insulation in buildings and of building elements using sound intensity - Part 1 : Laboratory conditions” was reviewed in order to make it as a new Korean Industrial Standard. Several main contents are discussed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.1187-1190
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• 2007

This study aims to induce acoustic environmental characteristics which could be used for soundscape design by carrying out factor analysis on sound source image and cognition analysis on subjects' responses on selective questions due to class differences. The results of this study are as follows ; Satisfaction rate differences on exterior acoustic environment due to sensitivity and residence year were revealed. After factor analysis of living sound sources' image, it is known that natural sound, traditional sound, socials traffic sound, rural sound, religious sound and the others are main factors. Social traffic sound is the most one that should be eliminated and traditional sound is selected as a most Korean-like sound. Natural sound is evaluated as the most one that should be preserved and the most retrospectively one.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.377-382
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• 2003

In our previous study, we have developed sound quality index for steady rumbling sound of passenger car. In this paper, we will study sound quality index for transient rumbling noise. The subjective evaluation of rumbling sound can be indicated to objective parameters by sound metrics of psychoacoustics and principal rumble component. And artificial neural network can be estimated complexity and nonlinear characteristics of relation between subjective evaluation and sound metrics. We applied to sound metrics and artificial neural network to development of sound quality index for transient rumbling sound of passenger car.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.849-854
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• 2001

A study on performance of the sound absorbing noise barrier is presented. Noise barrier of sound absorbing type is composed of the front panel, sound absorbing material, and back panel. For allowing sound path, front panel is usually perforated. The performance of the noise barrier is governed by the opening ratio of the perforated panel, sound absorption coefficient of the sound absorbing material. In this study, the effects of the opening ratio, diameter of the hole, thickness of the sound absorbing material are investigated. It is found that the thickness of the sound absorbing material must be at least 50 mm to ensure the required minimum NRC value 0.70, and the opening ratio is greater than 0.2. It is shown that the thickness of the back panel is crucial in providing required STL (Sound Transmission Loss) value. The performance of the developed noise barrier is measured, where its sound absorbing coefficient and sound transmission loss satisfy the criteria.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• 제13권6호
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• pp.445-451
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• 2003

Booming sound is one of the most important interior sound of a passenger car. The conventional booming noise research was focused on the reduction of the A-weighted sound pressure level. However A-weighted sound pressure level cannot give the whole story about the booming sound of a passenger car. In this paper, we employed sound metrics, which are the subjective parameters, used in psycoacoustics. According to recent research results. the relation between sound metrics and subjective evaluation is very complex and has nonlinear characteristics. In order to estimate this nonlinear relationship, artificial neural network theory has been applied to derivation of sound quality index for booming sound of a passenger car.