• Transactions of the Korean Society of Mechanical Engineers
• /
• v.10 no.5
• /
• pp.601-610
• /
• 1986

The acoustic intensity in the very near field of a vibrating surface reveals information about the location of sound sources and sinks. A system model of tennis racket was developed from simultaneous measurement of excitation force, surface vibration and the near field sound pressure. The characteristics of structural dynamics were obtained by standard experimental modal analysis techniques while the sound radiation characteristics were determined by estimating the acoustic intensity. In this paper, the information about vibration behviour was obtained by acoustic intensity method and some, experiments for verification were carried out. Close correlation was found between experimentally determined acoustic intensity and vibration mode patterns of the tennis racket.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2014.10a
• /
• pp.569-569
• /
• 2014

The interior vehicle noise due to the exterior aerodynamic field is an important topic in the acoustic design of a car. The air flow detached from the A-pillar and impacting the side windows are of particular interest as they are located close to the driver / passenger and provides a lower insulation index than the trimmed car body parts. This paper presents a numerical analysis method for a simplified vehicle model. The internal air cavity including trim component are included in the simulation. The car body includes the windshield and two side windows. The body is made of aluminum and trimmed with porous layers. The methodology proposed in this paper relies on two steps: the first step involves the computation of the exterior flow and turbulence induced non-linear acoustic field using CFD Code. The second step consists in the computation of the vibro-acoustic transmission through the window using the finite element vibro-acoustic solver Actran.

• Phonetics and Speech Sciences
• /
• v.10 no.2
• /
• pp.7-14
• /
• 2018

The paper investigates the acoustic characteristics of English fricatives in the TIMIT corpus, with a special focus on the role of voicing in rendering fricatives in American English. The TIMIT database includes 630 talkers and 2,342 different sentences, and comprises more than five hours of speech. Acoustic analyses are conducted in the domain of spectral and temporal properties by treating gender, voicing, and place of articulation as independent factors. The results of the acoustic analyses revealed that acoustic signals interact in a complex way to signal the gender, place, and voicing of fricatives. Classification experiments using a multiclass support vector machine (SVM) revealed that 78.7% of fricatives are correctly classified. The majority of errors stem from the misclassification of /θ/ as [f] and /ʒ/ as [z]. The average accuracy of gender classification is 78.7%. Most errors result from the classification of female speakers as male speakers. The paper contributes to the understanding of the effects of voicing and gender on fricatives in a large-scale speech corpus.

• Phonetics and Speech Sciences
• /
• v.1 no.3
• /
• pp.145-151
• /
• 2009

The purpose of this study was to investigate the acoustic characteristics of transgenders' voice. This study obtained acoustic measurements (F0, jitter, shimmer, and NHR) of 45 subjects (15 male adults, 15 female adults, and 15 transgender(male to female)) and compared acoustic measurements of the vowel /a/ produced by 3 groups. The MDVP was used to measure the acoustic parameters. A one-way ANOVA was used for statistical analysis. The results were as follow: Firstly, there was a significant difference among the 3 groups in F0. And F0 of transgenders was higher than that of male group and lower than that of female group. Secondly, there was a significant difference between male and transgender group in jitter and shimmer so that the transgender had a tendency to phonate roughly than male.

• Proceedings of the KIEE Conference
• /
• 2005.04a
• /
• pp.15-18
• /
• 2005

Switched reluctance drive does exhibit higher levels of vibration and acoustic noise than that of most competing drives. The main source of vibration in the switched reluctance drive is generated by rapid change of radial magnetic force when phase current is extinguished during commutation action. In this paper, some excitation method is proposed to reduce vibration and acoustic noise of the switched reluctance drive. The excitation strategies considered in this research are 1-phase, 2-phase and hybrid excitation method. 1-phase method is a conventional and 2-phase method is excited 2 phases simultaneously. The hybrid excitation has 2-phase excitation by long dwell angle as well as conventional 1-phase excitation. The vibration and acoustic noise are compared and tested. Suggested 2-phase and hybrid strategies reduce acoustic noise because the scheme reduces abrupt change of excitation level by distributed and balanced excitation.

• Journal of the Korean Society of Safety
• /
• v.18 no.2
• /
• pp.6-15
• /
• 2003

A method is presented for diagnosing the converter bearings by using acoustic emission. The flaking mechanism causing the large-scale bearing for furnace to flaw is investigated and a possibility of defect is verified by Finite Element method. he diagnosis logic is proposed fir detecting the flaw of a non-continuous rotating machine. It is proved that the acoustic emission energy can be used as a representative parameter for an acoustic event. Applying the method to the tilting bearings for steel mill in operation, the effectiveness of this logic is evaluated. It is shown that AE signal is generated only when the bearing is tilting, and the trend analysis can be focused upon this process.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2000.11a
• /
• pp.474-481
• /
• 2000

recently out-door stadium have been built not only for athletic sports but also various events and huge concerts and 50% of the roof of multi-purpose stadium have been covered by dome and the tendency of this kind of building type gradually increase, in spite of this kind of building tendency, the appearance of acoustic obstacle is serious and have little solution of this problem in acoustic-prevent building field. The purpose of this study is for analysis of acoustic Properties(SPL, RT60, RASTI) and answering of characteristics of echo through acoustic computer simulation in Seoul world cup stadium in the first instance.

• Journal of Ocean Engineering and Technology
• /
• v.33 no.5
• /
• pp.421-426
• /
• 2019

The directivity of an underwater sound source should be measured in an acoustically open field such as a calm sea or lake, or an anechoic water tank facility. However, technical difficulties arise when practically implementing this in open fields. Signal processing-based techniques such as a sound intensity method and near-field acoustic holography have been adopted to overcome the problem, but these are inefficient in terms of acquisition and maintenance costs. This study established a simple directivity estimation technique with data acquisition, filtering, and analysis tools. A numerical simulation based on an acoustic radiosity method showed that the technique is practicable for sound source directivity estimation in a diffused reverberant acoustic field like a reverberant water tank.

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

• Speech Sciences
• /
• v.9 no.3
• /
• pp.87-97
• /
• 2002

The purpose of this study is to analyze the speech duration in Korean-speaking aphasics. Five patients with nonfluent aphasia (2 with traumatic brain injury and 3 with strokes) and five normal adults participated in this experiment. The mean age in patients with nonfluent aphasia was $45.8\pm2.3$ years and $47.4\pm2.3$ years for the normal adults. The Computerized Speech Lab was used to evaluate the acoustic characteristics of the subjects. Voice onset time, vowel duration, total duration, hold and consonant duration were evaluated for the monosyllabic and the polysyllabic words. The patients with nonfluent aphasia did not show the voicing bar on hold area, however, it was seen in the normal persons in the intervocalic position. Explosion duration of glottalized stops in the intervocalic position was significantly prolonged in nonfluent aphasics in comparison with the normal persons. This suggestes that the laryngeal adjustment is disturbed in these patients. Consonant duration, vowel duration, and total duration of the polysyllabic words were significantly longer in the patients with nonfluent aphasia than those of the normal persons. These results demonstrate the disturbances in controlling articulatory muscles during sound production in patients with nonfluent aphasia. The objective and quantitative analysis based on the acoustic characteristics of nonfluent aphasics, will be very useful in therapeutic planning and on the the effects of speech therapy.