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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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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 32, Issue 6 - Nov 2013
Volume 32, Issue 5 - Sep 2013
Volume 32, Issue 4 - Jul 2013
Volume 32, Issue 3 - May 2013
Volume 32, Issue 2 - Mar 2013
Volume 32, Issue 1 - Jan 2013
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Acoustic Channel Formation and Sound Speed Variation by Low-salinity Water in the Western Sea of Jeju during Summer
Kim, Juho ; Bok, Tae-Hoon ; Paeng, Dong-Guk ; Pang, Ig-Chan ; Lee, Chongkil ;
The Journal of the Acoustical Society of Korea, volume 32, issue 1, 2013, Pages 1~13
DOI : 10.7776/ASK.2013.32.1.001
Salinity does not generally affect sound speed because it shows very small variations in the ocean. However, low salinity water appears in the Western Sea of Jeju Island every summer so that sound speed and sound propagation can change near sea surface. We calculated Sound Speed Profile (SSP) using vertical profiles of temperature and salinity, which were averaged over years of normal salinity and low salinity (<28 psu) from 30 years (1980~2009) at 3 sites of Korea Oceanographic Data Center (KODC). As a result, sound speed variation by low salinity alone was -5.36 m/s at sea surface and -1.35 m/s at 10m depth for low salinity environments. Gradient of SSP was positive down to 5 m depth due to decrease of sound speed near surface, leading formation of haline channel. Simulation of acoustic propagation using a ray model (Bellhop) confirmed the haline channel. Haline channel has formed 4 times while hydrostatic channel controlled by only pressure has formed 9 times for 30 years. The haline channel showed larger critical angles of rays than hydrostatic channel. Haline channel was also formed at some sites among 20 measurement sites in low salinity water mass which appeared on August
5-MHz Volume Backscattering Strength Measurements from Suspended Sediment Concentrations
Lee, Changil ; Choi, Jee Woong ;
The Journal of the Acoustical Society of Korea, volume 32, issue 1, 2013, Pages 14~21
DOI : 10.7776/ASK.2013.32.1.014
The erosion, suspension, and transport of sediment frequently occur in the coastal waters and estuarine. These processes often generate the so-called fluid mud layer, which is defined as a high-concentration aqueous suspension of fine grained sediment (> 10 g/l), consisting mainly of silt and clay-size particles. Therefore the high-resolution ultrasound is mostly used to detect or monitor the fluid mud layer. Because the sound attenuation tends to increase rapidly with the suspended sediment concentration, it is necessary to consider the accurate attenuation correction to estimate the backscattering strengths from the suspended sediment layers. In this paper, the volume backscattering strengths with various suspended sediment concentrations were measured using 5-MHz ultrasound signal in a small-scale water tank. The sound attenuation due to the viscosity and scattering from suspended sediment particles was predicted by the Richard`s model and applied to the sonar equation to estimate the volume backscattering strengths from the suspended sediment concentrations. For the case that the additional attenuation was not considered, the volume backscattering strengths increased to the concentration of 20 g/l, and over this point, the backscattering strengths were roughly constant. However, for the case that the attenuation due to the suspended sediment concentration was considered, the backscattering strengths increased with the concentration.
Extraction of Time Coherence Using Detection of Dominant Components for Underwater Acoustic Communication Channels at East Sea
Kim, Hyeonsu ; Kim, Jaeyoung ; Park, Gunwoo ; Kim, Seongil ; Chung, Jaehak ;
The Journal of the Acoustical Society of Korea, volume 32, issue 1, 2013, Pages 22~31
DOI : 10.7776/ASK.2013.32.1.022
In this paper, we propose a method that estimates the channel response from underwater communication signals with MMSE (Minimun Mean Squared Error) and detects dominant components automatically based on power of response components using CFAR (Constant False Alarm Rate). Statistical characteristics are analyzed with variation of magnitude and phase and time coherence via experimental data obtained by drifting transmitter and receiver. We show that bit error rate has small difference, 1.2 times, compared with the case using every channel information estimated within data period when estimation and equalization is performed with extracted characteristic obtained by the proposed method.
Design of a Multimode Piezoelectric Spherical Vector Sensor for a Cardioid Beam Pattern
Lim, Youngsub ; Lee, Jaeyoung ; Joh, Cheeyoung ; Seo, Heeseon ; Roh, Yongrae ;
The Journal of the Acoustical Society of Korea, volume 32, issue 1, 2013, Pages 32~42
DOI : 10.7776/ASK.2013.32.1.032
Typical underwater piezoelectric spherical sensors are omni-directional, thus can measure the scalar quantity sound-pressure-magnitude only with the limitation not being able to measure the direction of the incoming wave. This paper proposes a method to simultaneously measure both the magnitude and direction of the sound wave with the spherical sensor. The method divides the piezoceramic sphere of the sensor into eight elements, and distinguishes the magnitude and direction of the sound pressure by combining the output voltage of the elements in a particular manner. Further, through the analysis of the sensitivity variation in relation to the structural parameters like radius and thickness of the piezoceramic sphere, we have suggested the way to improve the sensitivity of the vector sensor.
Noise Analysis and Reduction Methods of the All-in One Window Ventilation System
Park, Chan-Jae ; Haan, Chan-Hoon ;
The Journal of the Acoustical Society of Korea, volume 32, issue 1, 2013, Pages 43~55
DOI : 10.7776/ASK.2013.32.1.043
The window ventilation system based on the heat recovery device was developed which make air ventilation possible without opening the windows. However, mechanical and aerodynamic noises were come to pass which annoyed people in rooms. In the present study, noise of new window ventilation system was measured in both general room and anechoic chamber. Also, the noise path was detected to find cause of noise generation and vulnerable area of the device. Sound absorptive and insulation materials were applied to mitigate the noise. Finally, an alternative noise control method was suggested which can satisfy with the indoor noise standards. As a result, it was shown that the cause of noise was the low transmission loss in the ventilation system. As a result, it was shown that the main noise source of the ventilation system was the blower and the major cause of noise was the low transmission loss of the ventilation system. It is also concluded that the noise levels complies with the noise standards of 40 dBA when 2 mm rubber sheet is applied inside the ventilation system.
Survey on the Use of MP3 Players of High School Students and the Effect to Their Hearing Thresholds
Hong, Ha Na ; Kang, Tong Ho ; Hong, Bin Na ;
The Journal of the Acoustical Society of Korea, volume 32, issue 1, 2013, Pages 56~63
DOI : 10.7776/ASK.2013.32.1.056
This study surveyed MP3 player usage and evaluated its effect on hearing thresholds in high school students. It is reported an increase in risk factors for hearing loss in adolescents that paralleled the increase in sales of MP3 players. A total of 538 students in two high schools in Gwangju province participated in this study. The students completed questionnaires about their MP3 player use and their pure tone hearing thresholds were tested at several frequencies. The questionnaire results indicated that 61.1%, of the students listened to music on MP3 players for more than one hour per day, 71.6% listened for four or more days per week, and 36.7% had listened for more than 3 years. Listening at a high volume of 60% of the maximum level was reported by 51% and they recognized having ear pains. The pure tone hearing threshold was found to be raised for the adolescents who had a long history of MP3 listening at high volume (p< 0.0001).
Adaptive Watermarking for MP3 Copyright Protections Using Psychological Acoustics
Lee, Kyeong-Hwan ;
The Journal of the Acoustical Society of Korea, volume 32, issue 1, 2013, Pages 64~70
DOI : 10.7776/ASK.2013.32.1.064
In this paper, we suggest a new audio watermarking method for audio contents copyrights that can efficiently provide protection from MP3 compression attacks. Watermarks were inserted at the coefficients repeatedly from low frequencies to high frequencies after DCT transform in commonly used Cox`s spread spectrum method. Because the methods using arbitrary coefficients are not effective, we use the new weight functions that make small losses for the watermark coefficients during attacks, using psychological acoustics. In the results of various sound clips, the suggested method had overall better outcomes than the Cox`s method by preserving watermarks and reducing distortions of the original sounds.
Multiple Audio Watermarking using Quantization Index Modulation on Frequency Phase and Magnitude Response
Seo, Yejin ; Cho, Sangjin ; Chong, Uipil ;
The Journal of the Acoustical Society of Korea, volume 32, issue 1, 2013, Pages 71~78
DOI : 10.7776/ASK.2013.32.1.071
This paper describes a multiple audio watermarking using Quantization Index Modulation (QIM) on frequency phase and magnitude response. Proposed embedding procedure is composed of two stage. At the first stage, the watermark is embedded on the frequency phase response using QIM. In the second stage, the watermark is embedded using adaptive QIM with the step-size that is adaptively determined using the maximum value of the frequency magnitude response of every frame. The watermark is extracted by calculating the Euclidean distance as the blind detection. The proposed method is robust against most of attacks of audio watermark benchmarking. For the Fourier attacks, the proposed method shows over 95% recovery rate.
Target Speech Segregation Using Non-parametric Correlation Feature Extraction in CASA System
Choi, Tae-Woong ; Kim, Soon-Hyub ;
The Journal of the Acoustical Society of Korea, volume 32, issue 1, 2013, Pages 79~85
DOI : 10.7776/ASK.2013.32.1.079
Feature extraction of CASA system uses time continuity and channel similarity and makes correlogram of auditory elements for the use. In case of using feature extraction with cross correlation coefficient for channel similarity, it has much computational complexity in order to display correlation quantitatively. Therefore, this paper suggests feature extraction method using non-parametric correlation coefficient in order to reduce computational complexity when extracting the feature and tests to segregate target speech by CASA system. As a result of measuring SNR (Signal to Noise Ratio) for the performance evaluation of target speech segregation, the proposed method shows a slight improvement of 0.14 dB on average over the conventional method.
A Network Coding Scheme with Code Division Multiple Access in Underwater Acoustic Sensor Networks
Seo, Bo-Min ; Cho, Ho-Shin ;
The Journal of the Acoustical Society of Korea, volume 32, issue 1, 2013, Pages 86~94
DOI : 10.7776/ASK.2013.32.1.086
In this paper, we propose a network coding scheme that is one of the most promising techniques for overcoming transmission errors in underwater acoustic communications. It is assumed that the proposed scheme operates in a Code Division Multiple Access (CDMA) network where multiple sensor nodes share the underwater acoustic channel in both the frequency and the time domains by means of orthogonal codes. The network topology deploys multi-hop transmission with relaying between multiple source nodes and one destination node via multiple relay nodes. The proposed scheme is evaluated in terms of the successful packet delivery ratio of end-to-end transactions under varying packet loss rates. A computer simulation shows that the successful delivery ratio is maintained at over 95% even when the packet loss rate reaches 50%.