• The Journal of the Acoustical Society of Korea
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• v.1 no.1
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• pp.37-44
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• 1982

In the mixed layer when the frequency approaches the cut-off frequency for the first mode of notmalmode theory, sound ceases to be trapped. Based on the data of surface sound velocities abtained during the period of 16 years in the Sea of Japan. A new cut-off frequency coefficient in the surface duct that will determine the miximum wave length for duct transimission of underwater sound has been calculated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.911-916
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• 2001

Structural acoustic modification method based on the structural mobility analysis is applied to reduce the structure-borne noise radiated from hard disk drive system. Sound intensity techniques and ODS(Operational Deflection Shape) techniques are also used in order to provide the structural acoustic information for the mobility modification. The sound intensity is for the acoustic visualization of the noise source locations, and the ODS is for the visualization of the vibration pattern and its dynamic characteristics of the noise sources. Using visualization information of sound and vibration, local structural input mobility is reduced in the frequency band of interest by designing asymmetrical wave-stringer structure in the wave-number domain as well as frequency domain. The overall sound pressure level is reduced by 4dB and its controlled sound power radiated from the disk drive is proved to under 2.8Bel in idle-spinning mode and 3.1 Bel in random-seeking mode, which are the lowest noise levels in the hard disk drive industry.

• Journal of the Korean Institute of Oriental Medical Informatics
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• v.14 no.2
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• pp.1-9
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• 2008

With the booming complementary medicine as a social trend of well-being, treatment by the sound waves of six kinds of syllables is believed to restore that healthy balance to the body. Sound therapy refers to a range of therapies in which sound is used to treat physical and mental conditions. Healing is done by transmitting beneficial sound to the affected area related to five viscera and six bowels. The healing sound may be produced by a voice. sound wave vibrations are to treat physical and mental conditions. In general, this therapy is based on the theory that all of life vibrates, including people's bodies. When a person's healthy resonant frequency is out of balance, physical and emotional health is affected. When a person's healthy resonant frequency is out of balance, physical and emotional health is affected. This paper focuses on the sound therapy by six syllables of 'hyu', 'huo', 'ho', 'sa', 'chi' and 'hui'.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.618-621
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• 2014

This research is to review the possibility of reducing the noise radiated from the tube exit by controling the sound reflection coefficient at the inclined exit. The sound reflection coefficient at the inclined exit of flanged tube was measured by both transfer function method and standing wave ratio method. Accuracy on the sound reflection coefficient measured by transfer function method was verified through comparison with sound reflection coefficient measured by standing ratio method. The flanged tube had lower sound reflection coefficient than the tube which have no flange. Also the sound reflection coefficient was decreased in accordance with increasing the inclined angle of unflanged tube.

• The Journal of the Acoustical Society of Korea
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• v.13 no.3
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• pp.5-15
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• 1994

In order to examine the propagation loss associated with water depth and bottom sediment type, an acoustic experiment was conducted in the Southeast Sea of Korea. A sound source was towed along the pre-defined tracks in about 5kts and the signal was simultaneously received at three bottom-moored hydrophones. The propagation loss of sound wave traveling along the isodepth was compared with that crossing the isodepth. The former case shows, in general, less loss than the latter. This trend is stronger as the distance between a source and a receiver increases. When sound wave propagates across the isodepth, we also find that the propagation loss is influenced by the upsloping and downslopoing conditions of wave propagtion. In general, the propagation loss under downsloping condition is smaller than that of upsloping condition, and the differences are as large as 10dB in some cases. However, little difference are found in the propagation loss depending on the bottom types : gravelly sand and sand-silt-clay. Meanwhile, the optimum propagation frequencies are found within range of 130-255Hz.

• The Journal of the Acoustical Society of Korea
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• v.8 no.1
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• pp.67-74
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• 1989

The reflection coefficients of the sound absorbing materials are obtained from the standing wave ratio in the standin wave tube. This method is rather laborious to find the sound pressure maximum and minimum. We devised new method for determination of the complex reflection coefficients of the materials. The sound pressures and the phases are measured at least three points along the axis of the tube. The complex reflection coefficients are determined from the measured values by least square method. The measured results for the glasswool with thickness of 5cm and density of $50kg/m^3$ and the steel plate with thickness of 1.5cm are in good agreement with those of the conventional method. It is possible to measure the complex reflection coefficients at low frequencies with short standing wave tube and to interface with the personal computer which is very useful for the handling of amount of samples.

• Explosives and Blasting
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• v.26 no.1
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• pp.39-48
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• 2008

Using Electronic Detonators which is well known for controlling vibration, we have been studying Orchestra Blasting Method, OBM, for many years to transform the unpleasant blasting sound to favorable sound in some job-sites such as tunneling and bench blasting which have to been taken place near some structures needed great care. In this study, we focus on rhythmical sense. First, we acquired individual wave from a shot. With the program named the Program Blasting Wave, PBW, it was analyzed and found that its best delay time was 34ms and 50ms was acceptable. Also, delay time was fitted into the music which was accepted after analyzing the rhythm. As a result, the blasting sound along with the music felt comfortable as if the music was played with base drum.

• The Journal of the Acoustical Society of Korea
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• v.20 no.1
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• pp.3-12
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• 2001

In physical modeling of plucked string instruments, the vibration of a string is typically simulated by the linear system. Currently the Digital Waveguides of J.O.Smith[1] are widely used to get a high quality sound of the plucked string instrument. He used the wave equation to derive the Digital Waveguides and emphasized the time variable. In this thesis, new model of plucked string is proposed to improve the sound quality emphasizing the spatial variable of the wave equation. In our model, we used the fixed sampling interval which is not dependent on the speed of the wave. So we could get more detailed description of wave movement by the time variable. As a result, the new model could produce a higher quality sound of plucked string instrument.

• The Journal of the Acoustical Society of Korea
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• v.34 no.2
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• pp.117-129
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• 2015

A parametric array is a nonlinear phenomenon that generates a narrow beam of low-frequency sound using the nonlinearity of the medium. The low-frequency sound so generated has a low sound pressure compared with that of sound generated directly. Consequently, a transducer that can generate a primary wave with high directivity and level is required. This study designed, fabricated, and evaluated a multi-resonance transducer as a parametric array source. The designs of the unit transducers and array transducer were based on an analysis model. The design process was repeated to fabricate the optimum transducer. The fabricated transducer array can generate a 189 dB, 190 dB primary wave level at 6.3 m and a 134 dB difference frequency wave using the parametric array phenomenon. The difference frequency wave has a frequency of 15 kHz and high directivity with an $8^{\circ}$ half power beam width in a $12{\times}18{\times}10m$ water tank.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.14 no.4
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• pp.265-268
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• 1981

The direction and spectra of underwater sound wave were a remarkable contrast to the sound wave in the air because of the difference of transmissive medium. The linear hydrophone array of passive system has so far been applied to find out the direction and spectra of underwater sound wave from the sources for many purposes. The conventional methods are generally classified into two systems such as, the system which varying frequency responses, other parameters and pattern of signal like an adaptive array controlled by internal feedback, and another system which obtaining maximum of S/N ratio by giving a appropriate delay and a weighting coefficient in the output of each hydrophone. The array device of passive system can easily change the amplitude and the phase of signal by separately controlled hydrophone. And here we introduce a method that the spectral analyzing and the direction finding can be simultaneously carried out using a linear array of hydrophones. By making a circular convolution of output of signal from each hydrophone with appropriate rectangular weighting coefficient on the array, a sharp response of single lobe directivity and the spectral analyzing by time averaging were simultaneously obtained. In tile computer simulation of the array system with the length of 250cm and the interhydrophone distance of l0cm the power levels of sound signals received from given array direction were 16dB higher than those from the other directions when processing with rectangular weightings, and 8dB higher when processing with rectangular sound signals and rectangular weightings.