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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
> Journal Vol & Issue
The Journal of the Acoustical Society of Korea
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Journal DOI :
The Acoustical Society of Korea
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Volume & Issues
Volume 30, Issue 8 - Nov 2011
Volume 30, Issue 7 - Oct 2011
Volume 30, Issue 6 - Aug 2011
Volume 30, Issue 5 - Jul 2011
Volume 30, Issue 4 - May 2011
Volume 30, Issue 3 - Apr 2011
Volume 30, Issue 2 - Feb 2011
Volume 30, Issue 1 - Jan 2011
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A Method For Improvement Of Split Vector Quantization Of The ISF Parameters Using Adaptive Extended Codebook
Lim, Jong-Ha ; Jeong, Gyu-Hyeok ; Hong, Gi-Bong ; Lee, In-Sung ;
The Journal of the Acoustical Society of Korea, volume 30, issue 1, 2011, Pages 1~8
DOI : 10.7776/ASK.2011.30.1.001
This paper presents a method for improving the performance of ISF coefficients quantizer through compensating the defect of the split structure vector quantization using the ordering property of ISF coefficients. And design the ISF coefficients quantizer for wideband speech codec using proposed method. The wideband speech codec uses split structure vector quantizer which could not use the correlation between ISF coefficients fully to reduce complexity and the size of codebook. The proposed algorithm uses the ordering property of ISF coefficients to overcome the defect. Using the ordering property, the codebook redundancy could be figured out. The codebook redundancy is replaced by the adaptive-extended codebook to improve the performance of the quantizer through using the ordering property, ISF coefficient prediction and interpolation of existing codebook. As a result, the proposed algorithm shows that the adaptive-extended codebook algorithm could get about 2 bit gains in comparison with the existing split structure ISF quantizer of AMR-WB (G.722.2) in the points of spectral distortion.
Underwater Noise Measurements on the Immersed Hydrofoil of High-Speed Vessel
Park, Ji-Yong ; Lee, Keun-Hwa ; Seong, Woo-Jae ;
The Journal of the Acoustical Society of Korea, volume 30, issue 1, 2011, Pages 9~16
DOI : 10.7776/ASK.2011.30.1.009
When a hydrofoil ship plies at high speed, there exist possibilities of collision with ocean mammals dwelling near the surface. An active sonar located within the immersed hydrofoil structure that provides the lift for the vessel, can be used for early warning of their presence. The proper functioning of the active sonar system depends on its ability to reject noise and pick up the target signal. In this article, we measured the noise on a hydrofoil of an operating ship with two flush-mounted hydrophones. The measurements were conducted for the purpose of (1) identifying the effect of operating state of machinery likes engine, cooler and generator (2) observing the change of noise depending on the measuring position (3) observing the change of noise with increasing ship speed. To verify our experiment, experiments were performed three times and the measured results are compared with other investigations and they show similarity to each other. The results are analyzed with frequency domain in order to apply to operating active sonar detecting system and focus on high frequency band within sonar`s operating frequency region. Through these experiments and analysis, it is expected that we can identify the generated noise around hydrofoil where active sonar is installed and these results lead us to design active sonar that could distinguish target signal from noise more effectively.
An Experiment on Reduction of Infrasonic Underwater Self-Noise
Lee, Seong-Wook ; Lee, Yong-Kuk ; Kim, Seong-Ryul ;
The Journal of the Acoustical Society of Korea, volume 30, issue 1, 2011, Pages 17~21
DOI : 10.7776/ASK.2011.30.1.017
The effects of screening hydrophones with open-cell foams for reduction of the infrasonic self-noise induced by the flow around hydrophones are investigated by at-sea experiment. Test results of the 10 ppi polyurethane open-cell foams with different thickness show that the foams of 1 cm and 3 cm thickness reduce the flow-induced self-noises up to 20 dB and 28 dB at the frequency band of 2-10 Hz, respectively.
Effects of the Complexity of 3D Modeling on the Acoustic Simulations and Auralized Sounds
Park, Chan-Jae ; Haan, Chan-Hoon ;
The Journal of the Acoustical Society of Korea, volume 30, issue 1, 2011, Pages 22~32
DOI : 10.7776/ASK.2011.30.1.022
The present study examined the effects of the complexity of the 3D models on the results of acoustic simulation which is the predominant tool of the acoustical design of buildings. Also, the effects of the 3D model on the auralized sounds were investigated. In order to carry out the study, four 3D models with different levels of complexity were introduced for a real auditorium which have different numbers of surfaces in the persuit of the guidance of odeon room acoustic software. The set-up of models was also based on the level of transition order of the program. And the acoustic experiments were performed measuring room acoustic parameters including SPL, RT, C80, D50. Acoustic computer simulations were performed using four different models. Then, the results of the computer modeling were compared with the measured acoustical parameters. In addition, sound sources were recorded in the field and auralized sounds were made in convolution with the impulse source made from acoustic modeling. Then, subjective tests were undertaken using auralized sounds. As the results, it was found that the result of the acoustic simulation were closer to the real room acoustic properties when 3D model was more particularly made. For the subjective test, the listening materials were acknowledged as similar with the real sound source when more complex 3D model was used. Then, it could be concluded that the complexity of the 3D model affects the results of the acoustic modeling as well as subjective tests.
Investigation of Sound Pressure Detection of Fiber Optic Sensor in Transformer Oil According to TLS and CW Laser Source
Lee, Jong-Kil ;
The Journal of the Acoustical Society of Korea, volume 30, issue 1, 2011, Pages 33~41
DOI : 10.7776/ASK.2011.30.1.033
To substitute TLS in the hybrid system which is combined with Sagnac interferometer and fiber bragg grating (FBG) it is necessary to investigate how the laser source (TLS and CW) and sensor material variate the response of fiber optic sensor. Two different hollow cylinder type mandrel materials are proposed which are PTFE and PTFE+carbon and 18 m optical fiber is wounded at the mandrel surface. CW laser source experiments had been done in the oil tank which is filled with transformer oil in the 1 kHz~20 kHz frequency range. Also Sagnac interferometer fiber optic sensor is combined with FBG called hybrid system and TLS used as a light source. Based on the experimental results PTFE sensor showed more higher magnitude of detection signal rather than carbon sensor and this result is agreement with the McMahon`s theoretical results. Phase variation is inversely proportional to the elastic modulus of the mandrel material. In PTFE fiber sensor, tunable laser source showed more higher performance rather than CW case. Therefore, TLS fiber optic sensor can be applied to the hybrid system which is combined with Sagnac and FBG.
A Preliminary Study on the Application of Compound Sources to Active Noise Barrier
Baek, Kwang-Hyun ;
The Journal of the Acoustical Society of Korea, volume 30, issue 1, 2011, Pages 42~48
DOI : 10.7776/ASK.2011.30.1.042
This preliminary study is about the application of the compound source to the active noise barrier system as control sources. A compound source is composed of two monopole sources but having opposite phase. However, both monopole sources in one compound source are not independently controlled. The source strength of monopole source close to the noise source is proportional to the other one. Therefore, the cost for the hardware system is cheaper than usual system but known to possibly having a similar performance in generating anti-noise acoustic field. In this study, using a simple active noise barrier system model having a non-reflective floor, the effectiveness of the system with compound sources is investigated through computer simulations and shows 30~40 % performance improvement of noise reduction.
Preliminary Study on the Effects of Monaural Beating Sound of Tires to Human Body
Baek, Kwang-Hyun ;
The Journal of the Acoustical Society of Korea, volume 30, issue 1, 2011, Pages 49~55
DOI : 10.7776/ASK.2011.30.1.049
The effects of monaural beating sound generated according to the number of tire pitch blocks to human body are measured from experiments, and the possibilities of similar positive effects of enhancing alpha waves in human brain are investigated. Due to the requirement of repeatability and measurement conditions, recorded sounds of the tire noise are used for the experiment in a quiet room and human responses are measured using HRV. Although the number of statistically meaningful results was small, it showed that positive human reactions are probably possible.
Correlations of Phase Velocities of Guided Ultrasonic Waves with Cortical Thickness in Bovine Tibia
Lee, Kang-Il ;
The Journal of the Acoustical Society of Korea, volume 30, issue 1, 2011, Pages 56~62
DOI : 10.7776/ASK.2011.30.1.056
In the present study, the phase velocities of guided ultrasonic waves such as the first arriving signal (FAS) and the slow guided wave (SGW) propagating along the long axis on the 12 tubular cortical bone samples in vitro were measured and their correlations with the cortical thickness were investigated. The phase velocities of the FAS and the SGW were measured by using the axial transmission method in air with a pair of unfocused ultrasonic transducers with a diameter of 12.7 mm and a center frequency of 200 kHz. The phase velocity of the FAS measured at 200 kHz exhibited a very high negative correlation with the cortical thickness and that of the SGW arriving after the FAS showed a high positive correlation with the cortical thickness. The simple and multiple linear regression models with the phase velocities of the FAS and the SGW as independent variables and the cortical thickness as a dependent variable revealed that the coefficient of determination of the multiple linear regression model was higher than those of the simple linear regression models. The phase velocities of the FAS and the SGW measured at 200 kHz on the 12 tubular cortical bone samples were, respectively, consistent with those of the S0 and the A0 Lamb modes calculated at 200 kHz on the cortical bone plate.