• The Journal of the Acoustical Society of Korea
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• v.40 no.6
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• pp.615-625
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• 2021

Prior to proposing appropriate standard for subway station platform, this study conducted field measurements to examine characteristics of room acoustics on platform of two subway stations. As a result of analyzing the longitudinal length of the platform, Sound Pressure Level (SPL) decreased (maximum difference : 14 dB), Reverberation Time (RT) tended to increase (maximum difference of 0.8 s ~ 1.5 s), and C50 and D50 were decreased (maximum difference: 5.9 dB ~ 9.1 dB and 31.8 % ~ 37.6 %, respectively) as measurement positions moved away from the sound source. The Interaural Cross-correlation Coefficient (IACC) did not show clear tendency, but it was lower than 0.3 in entire points. It is judged that the subway platform has non-uniform sound field characteristics due to various combinations of direct and reflective sound even though it is finished with a strong reflective material.This indicates that the room acoustic characteristics of the near and far sound field are clearly expressed depending on the source-receiver distances in the subway platform having a long flat shape with a low height compared to the length.Therefore, detailed architectural and electric acoustic design based on the characteristics of each location of speaker and sound receiver in the platform is required for an acoustic design with clear sound information at all positions of the platform.

• The Journal of the Acoustical Society of Korea
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• v.42 no.1
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• pp.50-56
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• 2023

The hydroxyl radical (·OH) and superoxide anion radical (·O₂^- ) generated by the shock wave generated during ultrasonic cavitation collapse in TiO₂ suspension are highly useful because they can sterilize and disinfect. For practical use as a sterilization method without any chemicals, in this study, we proposed a method for evaluating the generation of radicals generated by high-intensity ultrasound emitted to titanium dioxide suspension. In the proposed method, the sonoluminescence phenomenon, which emits light by ultrasonic cavitation decay energy, was utilized, and the degree of radical generation was evaluated through the amount of light energy by sonoluminescence. As a result, even at a low concentration of titanium dioxide of 0.02 wt%, light energy 5 times higher than in the absence of titanium dioxide was received. After that, as the concentration increased by 0.1 wt%, the luminous intensity of sonoluminescence increased linearly by about 14.8 × 10^-12 lm. Therefore, it was confirmed that the radicals generated by radiating high-intensity ultrasound to the titanium dioxide suspension increased linearly as the concentration of titanium dioxide increased within a given concentration range.

• The Journal of the Acoustical Society of Korea
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• v.42 no.1
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• pp.25-31
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• 2023

In order to estimate the radial speed of an underwater object so-called target with active sonar, Continuous Wave (CW) pulse is generally used, but if a target is slow and at near distance, it is not easy to estimate the radial velocity of the target due to acoustic reverberation in the ocean. In 2017, Wang et al. utilized broadband signal of two Hyperbolic Frequency Modulation (HFM) pulses, which is known as a doppler-invariant pulse, with equal frequency band and in opposite sweep directions to overcome this problem and successfully estimate the radial speed of slow-moving nearby target. They demonstrated the estimation of the radial velocity with computer simulation using the parameters of two HFM starting time differences and receiving times. However, for it uses two HFM pulses with equal frequency, cross-correlation between the two pulses negatively affect the detection performance. To mitigate this cross-correlation effect, we suggest using two different band HFM with the opposite sweep directions. In this paper, a method of radial velocity estimation is derived and simulated using two HFM pulses with the pulse length of 1 second and bandwidth of 400 Hz. Applying the suggested method, the radial velocity was estimated with approximately 6 % of relative error in the simulation.

• The Journal of the Acoustical Society of Korea
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• v.42 no.1
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• pp.7-15
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• 2023

Recently, as interest in air quality in vehicles increases, the use of fine dust detection sensors for air quality measurement is becoming common. An axial-flow fan is inserted in the fine dust sensor installed in the air conditioning system in the vehicle to prevent dust from sinking directly on the sensor. When the sensor operates, the flow noise caused by the rotation of the axial-flow fan acts as a major noise source of the fine dust sensor. flow noise is recognized as one of the product competitiveness of fine dust sensors. In this study, the noise was gradually reduced at the same flow rate by improving the flow performance of the small axial flow fan. First, a virtual fan performance tester consisting of about 20 million grids was developed to analyze the aerodynamic performance of the target small axial-flow fan. In addition, the flow field was simulated by using compressible Large Eddy Simulation for direct computation of flow noise as well as high-accurate prediction of flow rate. The validity of numerical method are confirmed through the comparison of predicted results with experimental ones. After the effects of pitch angle on flow performance were analyzed using the verified numerical method, the pitch angle was determined to maximize the flow rate. It was found that the flow rate was increased by 8.1 % and noise was reduced by 0.8 dBA when the axial-flow fan with the optimum pitch angle was used.

• The Journal of the Acoustical Society of Korea
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• v.42 no.2
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• pp.102-111
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• 2023

Automatic Music Transcription (AMT) is a task that detects and recognizes musical note events from a given audio recording. In this paper, we focus on reducing the latency of real-time AMT systems on piano music. Although neural AMT models have been adapted for real-time piano transcription, they suffer from high latency, which hinders their usefulness in interactive scenarios. To tackle this issue, we explore several techniques for reducing the intrinsic latency of a neural network for piano transcription, including reducing window and hop sizes of Fast Fourier Transformation (FFT), modifying convolutional layer's kernel size, and shifting the label in the time-axis to train the model to predict onset earlier. Our experiments demonstrate that combining these approaches can lower latency while maintaining high transcription accuracy. Specifically, our modified model achieved note F1 scores of 92.67 % and 90.51 % with latencies of 96 ms and 64 ms, respectively, compared to the baseline model's note F1 score of 93.43 % with a latency of 160 ms. This methodology has potential for training AMT models for various interactive scenarios, including providing real-time feedback for piano education.

• The Journal of the Acoustical Society of Korea
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• v.42 no.6
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• pp.565-571
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• 2023

With the introduction of the post-verification system, the measurement of floor impact noise performance on-site has become mandatory, and the evaluation method has changed. To track the performance changes since the policy implementation, research is needed on how the characteristics of heavyweight impact sound change according to the varied evaluation method. In this study, we analyzed the contribution rate of the frequency band-specific sound pressure level on the single-number quantity for a multi-family housing unit with the same floor plan and floor structure, comprising 59 households, based on the changed impact sources and evaluation indicators. It is difficult to compare simply because the method of calculating contributions by frequency band according to the single-day evaluation is different, but the average contribution rate of 63 Hz was 80.8 % in the evaluation method before the introduction of the post-confirmation system (Tire measurement and evaluated as L'_i,Fmax,AW), and the average contribution rate of 125 Hz was 19.2 %. The current evaluation method (rubber ball measurement and evaluation as L'_iA,Fmax) shows that the contribution rate has decreased to 33.1 % on average at 50 Hz ~ 80 Hz, 58.7 % on average at 100 Hz ~ 160 Hz, 6.9 % on average at 200 Hz ~ 315 Hz, and 1.3 % on average at 400 Hz ~ 630 Hz. This result is a case analysis for the target apartment house, and it is necessary to analyze measurement data for more diverse apartment houses.

• The Journal of the Acoustical Society of Korea
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• v.29 no.5
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• pp.303-313
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• 2010

This paper describes an acoustic communication receiver structure, which is designed for QPSK (Quadrature Phase Shift Keying) signal with 25 kHz carrier frequency and 5 kHz symbol rate, and takes samples from received signal at 100 kHz sampling rate. Based on the described receiver structure, optimum design parameters, such as number of taps of FF (Feed-Forward) and FB (Feed-Back) filters and forgetting factor of RLS (Recursive Least-Square) algorithm, of joint equalizer are determined to minimize the BER (Bit Error Rate) performance of the joint equalizer output symbols when the acquisition data in shallow water using implemented acoustic transducers is decimated at a rate of 2:1 and then enforced to the input of receiver. The transmission distances are 1.4 km, 2.9 km, and 4.7 km. Analysis results show that the optimum number of taps of FF and FB filters are different according to the distance between source and destination, but the optimum or near optimum value of forgetting factor is 0.997. Therefore, we can reach a conclusion that the proper receiver structure could change the number of taps of FF and FB filters with the fixed forgetting factor 0.997 according to the transmission distance. Another analysis result is that there are an acceptable performance degradation when the 16-tap-length simple filter is used as a low-pass filter of receiver instead of 161-tap-length matched filter.

• The Journal of the Acoustical Society of Korea
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• v.26 no.4
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• pp.136-143
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• 2007

This experiment was performed to find out the effects of the cicadas' songs on the psychological responses in adolescents. As a basic coulee, the experiment to set up 'Acceptable & Unacceptable' was performed. As a further coulee, five kinds of the cicadas' songs heard frequently were analyzed and adjectives expressing the feeling to cicadas' songs were factor-analyzed, and psychological responses to auditory sensations were analyzed through regression equations. As a result, the effect of the Cryptotympana atrata's song, the Meimuna opalifera's song and the traffic noise are similar in the degree of disturbing the meditation but they are less disturbing than the white noise. The experiment for adjectives expressing was performed, because it is possible that cicadas' songs affect adolescents as a noise. Cicadas' songs can be expressed with three kinds of factors. First factor is [Annoyance], second factor is [Strength] and third factor is [Rhythm]. The first factor dominates in the songs of the Cryptotympana atrata and the Platypleura kaempferi who generate steady sound, and the third factor dominates in the songs of the Meimuna opalifera, the Leptosemia takanonis and the Oncotympana fuscata who generate fluctuating sounds. The loudness of sound didn't affect on the third factor but the emotional values of the fist and the second factors are linearly proportional to the loudness. The analysis results of the first factor associated with noise showed that the annoyance of adolescents is increased in the order of white noise - the Platypleura kaempferi - the Cryptotympana atrata, if the loudness of sounds are generated equally.

• The Journal of the Acoustical Society of Korea
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• v.43 no.1
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• pp.1-8
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• 2024

For measuring the performance of passive sonars, we usually consider the maximum Detection Range (DR) under the environment and system parameters in operation. In shallow water, where sound waves inevitably interacts with sea surface or bottom, detection generally maintains up to the maximum range. In deep water, however, sound waves may not interact with sea surface or/and bottom, and thus there may exist shadow zones where sound waves can hardly reach. In this situation, DR alone may not completely define the performance of each sonar. For complete description of sonar performance, we employ the concept 'Robustness Of Detection (ROD)'. In the coastal region of the East Sea, the spatial variations of water masses have close relations with DR and ROD, where the two parameters show reverse spatial variations in general. The spatial and temporal analysis of the temperature by employing the Empirical Orthogonal Function (EOF) shows that the 1-st mode represents typical pattern of seasonal variation and the 2-nd mode represents strength variations of mixed layers and currents. The two modes are estimated to explain about 92 % of the variations. Assuming two types of targets located at the depths of 5 m (shallow) and 100 m (deep), the passive sonar performance (DR) gives high negative correlations (about -0.9) with the first two modes. Most of temporal variations of temperature occur from the surface up to 200 m in the water column so that when we assume a target at 100 m, we can expect detection performance of little seasonal variations with passive sonars below 100 m.

• The Korean Journal of Emergency Medical Services
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• v.12 no.2
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• pp.59-69
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• 2008

Purpose : This study aims to provide basic data to establish an effective emergency medical service system by analyzing health educator' understanding and use of emergency medical service system at schools. Method : 93 questionnaires from 200 elementary, middle and high school nurses in the city D were collected from May 26 to July 7, 2008 and ${\chi}^2$ analysis and frequency analysis were carried out with SPSS win PC 14.0. Results : 1. As for emergency contact points, 3(3.30%) answers 'they do not have any knowledge', 40(43.96%) said 'they have some idea' and 48(52.75%) said 'they do know about it'. Among 24 respondents who have less than five years of working experience, 2(8.33%), 16(66.67%) and 6(25.00%) answered 'have no knowledge', 'a little knowledge' and 'clear knowledge on it' respectively. As for 9 who have 6-10 years of career, 1(12.50%), 4(50.00%) and 3(37.50%) answered 'have no knowledge', 'a little knowledge' and 'clear knowledge on it' respectively. Among 32 respondents who have 11~20 years, there were no respondents with no knowledge on the given question, and 9(29.03%) said they have some understanding and 22(70.97%) answered they have clear understanding on the topic. From this result, it can be said that there is statistically meaningful differences among different working year groups with ${\chi}^2=16.583$ and p= .010. 2. As for 119 emergency contact in the given district, 24(29.63%), 30(37.04%) and 27 (33.33%) answered 'do not know', 'know' and 'know very well' respectively. As for the question to ask whether they know Emergency Medical Information Center 1339, 66(70.97%) answered 'Yes' and 27(29.03%) answered 'No'. When it comes to emergency contact numbers and list of hospitals, 59(63.44%) said 'they have some list', 20(21.51%) answered 'they have well established contact network' and 14(15.05%) said 'they have none'. 3. As for the use of 119 service at the time of emergency at schools, 59(63.44%), said 'Yes' and 12(12.90%) answered 'No'. Among those who said 'yes', 29(31.18%), 24(25.81%) and 5(5.38%) answered they have used the service 1-2, 3-5 and 6-10 times respectively. Conclusion : In order to ensure health educator to effectively deal with emergency situations at schools, there should be special activities to enhance health educator' understanding on 119 and Emergency Medical Information Center 1339 and at the same time, a system should be established to connect schools, 119 in a given district, hospitals and Emergency Medical Information Center 1339.