• The Journal of the Acoustical Society of Korea
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• v.19 no.5
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• pp.20-26
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• 2000

In speaker verification system the HMM(hidden Markov model) parameter updating using small amount of data and the priori threshold decision are crucial factor for dealing with long-term variability in people voices. In the paper we present the speaker model updating technique which can be adaptable to the session-to-intra speaker variability and the priori threshold determining technique. The proposed technique decreases verification error rates which the session-to-session intra-speaker variability can bring by adapting new speech data to speaker model parameter through Baum Welch re-estimation. And in this study the proposed priori threshold determining technique is decided by a hybrid score measurement which combines the world model based technique and the cohen model based technique together. The results show that the proposed technique can lead a better performance and the difference of performance is small between the posteriori threshold decision based approach and the proposed priori threshold decision based approach.

• The Journal of the Acoustical Society of Korea
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• v.31 no.6
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• pp.399-409
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• 2012

In this paper we propose a method for measuring the shear modulus of an ultrasound soft tissue phantom using an acoustic radiation force. The proposed method quantitatively determines the shear modulus based on the rise time of a displacement induced by an acoustic radiation force at the focal point of a focused ultrasound beam. The shear wave speed and shear modulus obtained from the proposed method and a shear wave propagation method were compared to verify the validity of the proposed method. In the shear wave propagation method, the shear modulus is first computed by measuring the propagating speed of a shear wave induced in a phantom by a limited-diffraction transmit field, and then was compared to that obtained with the proposed method in an ultrasound data acquisition system calibrated based on the first computed shear modulus. The relative errors between the two methods were found to be 4% for shear wave speed and less than 9% for shear modulus, confirming the usefulness of the proposed method.

• The Journal of the Acoustical Society of Korea
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• v.39 no.5
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• pp.390-399
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• 2020

Underwater ambient noise was measured at the eastern and western costal sites of Jeju Island where the water depth was 20 m by a hydrophone moored at mid-depth (10 m) for 4 months. These eastern and western sites were selected as potential sites for offshore wind power generator and the current wave energy generator, respectively. Ambient noise was affected by environmental data such as wind and wave, which were collected from nearby weather stations and an observation station. Below 100 Hz, ambient noise was changed about 5 dB ~ 20 dB due to low and high tide. Below 1 kHz, wave and wind effects were the main source for ambient noise, varying up to 25 dB. Ambient noise was strongly influenced by wave at lower frequency and by wind at higher frequency up to over 1 kHz. The higher frequency range over 10 kHz was influenced by rainfall and biological sources, and the spectrum was measured about 10 dB higher than the peak spectrum level from Wenz curve at this frequency range.

• The Journal of the Acoustical Society of Korea
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• v.30 no.8
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• pp.436-445
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• 2011

In this paper, equivalent properties of 2-2 mode piezocomposites were studied. Variation of the properties of 2-2 mode piezocomposites was analyzed by the finite element method, and the result was compared with experimental measurement data to confirm the validity of the analysis. The equivalent properties of a single phase material to represent the piezocomposite composed of PZT-5H and polymer were derived by the asymptotic averaging method. Accuracy of the derived equivalent properties was enhanced by minimizing the discrepancy between the impedance spectra of full 2-2 piezocomposite and equivalent single phase material resonators of various vibration modes by the least square method. The equivalent properties of 2-2 piezocomposites derived in this study can be utilized to the design of diverse acoustic sensors.

• The Journal of the Acoustical Society of Korea
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• v.35 no.6
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• pp.466-472
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• 2016

In this work, a medical linear array ultrasonic transducer working in the range of 20 MHz has been developed for high-resolution ultrasonic imaging. After devising the structure of the transducer suitable for the transmission of high-frequency waves, we optimized the dimension of constituent components. Then, the process to fabricate the transducer was developed to realize the designed structure, and a prototype of the transducer was fabricated and characterized. The center frequency of the fabricated transducer was measured to be 19 MHz, and the fractional bandwidth to be 84.5 %, and the standard deviation of the sensitivity over the entire channels to be 0.74 dB. These measurement results showed good agreement with design data, which confirmed the validity of the high frequency ultrasonic transducer structure developed in this work. It was confirmed that the developed transducer with new structure had wider frequency bandwidth and uniform sensitivity than a conventional 20 MHz transducer.

• The Journal of the Acoustical Society of Korea
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• v.23 no.7
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• pp.497-502
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• 2004

Both ultrasonic velocity at 3 MHz and absorption coefficient in the frequency range of 0.2-2 MHz were measured for poly (sodium 4-styrenesulfonate) aqueous solution over the concentration range of 5 to 25 % by weight. Pulse echo overlap method was employed to measure the ultrasonic velocity over the temperature range of 10-90 ℃ and the high-a ultrasonic resonator method was used for the absorption coefficient measurement at 20 ℃. The velocity exhibited a maximum value at approximately 55. 59, 63. 67, and 71 ℃ in 25, 20. 15, 10. and 5 wt% solutions, respectively. The velocity increased with poly (sodium 4-styrenesulfonate) concentration at a given temperature. The concentrations dependences of the relaxation frequency and amplitude showed that the relaxation around 200 kHz is related to the structural fluctuations of polymer molecules, such as the segmental motions of the polymer chains and that around 1 MHz resulted from the proton transfer reaction of the oxygen sites of SO₃. Both the absorption and the shear viscosity increase with the Polymer concentration. but decrease with temperature.

• The Journal of the Acoustical Society of Korea
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• v.31 no.5
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• pp.309-316
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• 2012

This paper suggest configuration method of small-size system and design method of module using multi power. In particular module designed to focus on PDN(Power Distribution Network) and filter configuration method to improve the characteristics of noise sensitive analog IC. For the prevention of high-voltage noise, manufactured module is used the ground-isolated technique and via stitching, and is connected grounds with a series of filters. In this paper, so we analyzed PDN structure through the simulation using lumped modeling and confirmed through measurement. Simulation results, when connecting 4.7uH inductor, we made certain that noise of -7dB decreases much more than when it did not. And it was confirmed 12% less than Background Noise.

• The Journal of the Acoustical Society of Korea
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• v.38 no.5
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• pp.558-567
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• 2019

When used for broadcasting, multipurpose halls need to accommodate various types of programs such as speeches, Korean traditional music, musicals, pop music, and concerts. Therefore, multipurpose halls must meet a wide range of electric and architectural acoustic demands. However, there are few ways to alter acoustic environments for multipurpose halls, given these different demands. The current study investigates the effects of banners on acoustic environments in the presence of an acoustic shell or electric acoustic system. The results indicate that the installation of a 15% banner of wall area could vary the range of reverberation time ($T_{30}$) by 0.12 s, EDT (Early Decay Time) by 0.15 s, clarity of music ($C_{80}$) by 0.76 dB, and clarity of speech ($D_{50}$) by 6.43 % under different measurement circumstances. A computer simulation that enlarges the banner size to 40 % of the wall area varies the reverberation time from 0.11 s to 0.55 s depending on the room environment.

• The Journal of the Acoustical Society of Korea
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• v.37 no.6
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• pp.387-395
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• 2018

In this study, the noise characteristics of the propeller tip vortex cavitation and its inception were analyzed experimentally. Generally, tip vortex cavitation is the first appeared cavity that occurs in a propeller. If propeller tip vortex cavitation is appeared, the level and characteristics of underwater radiated noise changes dramatically compared with the non-cavitating propeller. Therefore, it is very important to analyze the noise characteristics of the propeller cavitation and to detect the cavitation inception in the development of the propulsion system for military vessel and underwater weapon system. The change of noise characteristics due to the inception and growth of the propeller tip vortex cavitation was analyzed. Various imaging-noise measurement and analysis technique were used to determine the inception of propeller cavitation.

• The Journal of the Acoustical Society of Korea
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• v.38 no.2
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• pp.154-159
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• 2019

When measuring the radiating noise of an underwater moving source, the range information between the acoustic source and the receiver is an important evaluation factor, and the measurement standards such as a receiver position, a moving source depth and a speed are set. Although there is a method of using the cross correlation as a method of finding the range of the underwater moving source, this method requires a time synchronization process. In this paper, we proposed the method to estimate the range by comparing the Doppler frequency difference of the theoretically calculated multipath signal with the Doppler frequency difference of the multipath signal estimated from the received signal. The proposed method does not require a separate time synchronization process. Simulations were performed to verify the performance, and the ranging error of the proposed method reduced by about 95 % than that of the conventional method.