• The Journal of the Acoustical Society of Korea
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• v.41 no.6
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• pp.637-646
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• 2022

Sub-arrays of arbitrary conformal array have different geometric shape through steering direction, thus the beam patterns of sub-arrays are always non-uniform. In this paper, we apply the beam pattern synthesis method using convex optimization into the conformal array, and shows the improvement of uniformity of beam performance. The simulation is performed with the conformal array of cut-sphere shape. As a result, the standard deviation of 3 dB beamwidth in elevation is greatly reduced but the directivity index is also reduced. To alleviate this trade-off, we propose a convex optimization using a shading function.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.7
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• pp.462-469
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• 2015

This study was carried out to examine characteristics of various acoustic indicators evaluating speech intelligibility such as reverberation time(T₃₀), D₅₀, C₅₀ and speech transmission index(STI) in Korean elementary school classrooms. Results showed that mean T₃₀ at middle frequencies(500 Hz to 2000 Hz) measured in 9 classrooms was about 0.75 s, which exceeds a regulation specified on American National Standards(ANSI); 0.60 s. Mean D₅₀, C₅₀ and STI were 60 % to 66 %, +2 dB to +3 dB, and 0.65, respectively. The maximum difference in D₅₀ and C₅₀ according to different receiver points in a classroom was 13 % and 2.5 dB, while the maximum difference in T₃₀ was 0.03 s. Whereas STI measured in classrooms has relatively low correlation with other indicators, correlation between D₅₀ and C₅₀ was high, R²=.9964. In addition, T₃₀ and C₅₀ were fitted well as logarithmic regression curve with R²=.9610. It was +3.73 dB in C₅₀ and 68 % in D₅₀ which are the value corresponding to 0.60 s in T₃₀ on this curve.

• The Journal of the Acoustical Society of Korea
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• v.27 no.6
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• pp.271-278
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• 2008

The electro-mechanical characteristics were theoretically analyzed for the wideband ultrasonic transducer made of non-uniform thickness piezoelectric vibrator. This paper proposes a combination of exponential functions which describes the thickness variation along the length of the vibrator to derive the input admittance and power transfer function of the transducer. The bandwidth and the power transfer function of the transducer were investigated while the lateral shape of the vibrator changes. The results showed there is an optimum shape for the wideband characteristics of the transducer, and the bandwidth has increased up to over 100% as the ratio of minimum value of thickness to maximum value decreases. However, the power transfer function had a downward trend as the ratio of thickness decreases. Also we confirmed that even though the value of transfer function increases as the length of the piezoelectric vibrator increases, the shape providing wideband characteristics is very limited. It means that precision processing is required to manufacturing a wideband ultrasonic transducer with high efficiency.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.4
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• pp.314-321
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• 2000

In order to obtain the fundamental data on the auditory thresholds of fishes for catching method using low frequency sound, the auditory thresholds of coralfish Chromis notatus were measured in the presence of masking noise in the spectrum level range of 73~83dB re l$\mu$Pa/√Hz by heartbeat conditioning technique using pure tones coupled with a delayed electric shock. Critical ratios were about 23~41dB at measurement frequency, The critical ratio increased almost linearly with increasing frequency from 500Hz. The noise spectrum level at the start of masking was about 60~65dB. This suggests that hearing of coralfish is masked in the natural environment with the noise spectrum level above 60dB. The sound pressure level of which the signal sound of 300Hz is recognized by coralfish under the ambient noise is above 88dB and the critical ratio of them is above 23dB. The hearing index of coralfish with ambient noise was 81.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.3
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• pp.234-243
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• 2012

In this paper, a sound quality indices for the evaluation of vehicle intake and exhaust noise were developed through a correlation analysis of objective measurement data and subjective evaluation data. At first, intake and exhaust orifice noise were measured at the wide-open throttle sweep condition. And then, acoustic transfer function between intake orifice noise and interior noise at the steady state condition was measured. Also, acoustic transfer function for exhaust system was measured as the same method. Simultaneously, subjective evaluation was carried out by the paired comparison and semantic differential method by 27 engineers. Next, the correlation analysis between the psycho-acoustic parameters derived from the measured data and the subjective evaluation was performed. The most critical factor was determined and the corresponding sound quality index for the intake and exhaust noise was obtained from the multiple factor regression method. At last, the effectiveness of the proposed index was investigated.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.5
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• pp.345-351
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• 2015

Sounds of electrically powered vehicle components such as window lift system, roller blind, etc., are required to be more comfortable and not to irritate the people emotionally. In this paper, a study was conducted to identify the significant sound quality metric and compose the luxuriousness sound quality index of electrically powered vehicle roller blind which is part of vehicle sunroof system. Before conducting subjective evaluation, sound characteristics of roller blind was analyzed and set the target operating sound for subjective evaluation. Thus, transfer sound of roller blind which has the characteristics of sound modulation was used for subjective evaluation. Multiple linear regression analysis was carried out by chosen Zwicker's metrics which are pointed by comments of jurors. Loudness and sharpness related metrics are prime metrics in luxuriousness sound quality index we composed. Also, effect of roller blind assay when it is attached to real vehicle was identified to evaluate the validity of index.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.9
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• pp.614-619
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• 2015

The purpose of this study is that developing the index which evaluate sound quality of door latch and improving its sound quality through that results. For that, various operating sound of door latch was used for jury test. Loudness and sharpness related metrics are dominant in sound quality index we developed. This research investigate the main transfer path of its operating sound through sound field visualization and get conclusion that could reduce the impact sound of door latch. Therefore, we could verify sound quality improvement of modified product by using sound quality index.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
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• v.19 no.2
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• pp.89-95
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• 2008

Subjective voice evaluation is necessary and important to assess the voice disorders in addition to objective voice evaluation. Subjective voice evaluation is divided into examiner and examinee subjective voice assessment. The examiner assessment represents perceptual judgment to the patient's voice such as GRBAS scale, Buffalo voice profile, consensus auditory perceptual evaluation of voice (CAPE- V) and so on. The examinee assessment consists of indirect method including voice handicap index (VHI), voice outcome survey (VOS), voice symptom scale (VoiSS), voice related quality of life (V-ROQL) and direct method which is called patient's self-subjective voice rating. This review article describes a general rule, advantages and pitfalls about GRBAS scale, VHI and patient's self-subjective voice rating which are presently most representative voice assessment tools.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.1
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• pp.179-184
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• 2019

In this paper, we propose a design method of Active Noise Control (ANC) that reduces perceived level of the residual noise. A FELMS (Filtered-E Least Mean Squares) algorithm is used for the ANC system and the NC (noise criteria) is applied as an evaluation criterion of the residual noise. With this structure, we present the allowable spectral shape of the noise shaping filter that minimizes the NC index within the effective operating frequency band of the ANC, and showed that the filter satisfying in the criterion has a lower NC value than the psychoacoustic-based filter used in the previous studies.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.7
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• pp.3048-3056
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• 2012

The purpose of this study was to investigate VHI, V-RQOL, and vocal characteristics of a teacher and singer. 56 subjects were participated in this study (20 subjects are a teacher with vocal nodule, 20 subjects are a singer with vocal nodule, and 16 subjects are normal speakers). All subjects completed the VHI, V-RQOL, and vocal characteristics were measured using CSL 4500(Kay Pentax. USA). 21 subjects completed the VHI, V-RQOL, and vocal evaluation using CSL 4500 twice to assess test-retest reliability. A statistical analysis was performed using the Statistical Package for Social Sciences 18.0 (SPSS Inc, Chicago, IL). The VHI and V-RQOL showed that the teacher and singer group were significantly higher than those of the control group in functional, physical and emotional aspects(p<0.05). the acoustic analysis using CSL 4500 showed the teacher and singer group were significantly higher than those of the the control group in fundamental frequency related variables, fundamental perturbation related variables, amplitude perturbation related variables, noise related variable, and tremor related variables(p<0.05). Conclusionally, the teacher and singer group recognized their voice problems as a serious physico-functional aspects.