• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.3
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• pp.436-442
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• 2022

In this paper, the performance of the selective combining according to the channel selection decision method of frequency diversity is evaluated in the underwater frequency selective channel. The underwater acoustic channel in the shallow sea has a complex multipath characteristic by combining various environmental factors such as boundary surface reflection and sound wave refraction according to the water temperature layer. In particular, frequency selectivity due to multipath causes energy fluctuation in a communication channel, which reduces SNR (Signal to Noise Ratio) and deteriorates communication performance. In this paper, we applied the frequency diversity technique using multiple channels to secure the communication performance according to the frequency selectivity by multipath. For each channel, 4-FSK (Frequency Shift Keying) and selective combining were applied, the performance was evaluated by applying the maximum value, average value, and majority decision of the signal in order to decide the demodulation channel selection of the selective combining.

• The Journal of the Acoustical Society of Korea
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• v.43 no.4
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• pp.391-399
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• 2024

In order to analyze the distribution of sound fields radiating from a circular plate vibrated by a Langevin transducer, a theoretical analysis model was derived. The boundary conditions of the driving area and fixed boundary area were appropriately applied to the equation of motion of the vibrating plate, which was derived by L. Rayleigh. By calculating the vibration displacement distributed on the surface of the vibrating plate using the derived analysis model and then calculating the sound field formed by the ultrasonic waves radiating from it, it was confirmed that the radiation characteristics vary significantly depending on the area of the vibrating plate. For comparison, a simulation of the same system was performed using the COMSOL program, a finite element method, and showed good agreement with the theoretical calculation results, confirming the effectiveness of the theoretical analysis model derived in thisstudy. It is expected that the theoretical analysis model derived from this study can be used in the design and development of related devices, such as in the ultrasonic chemistry field.

• The Journal of the Acoustical Society of Korea
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• v.34 no.5
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• pp.385-393
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• 2015

The speed of train has rapidly been increased in accordance with the developed railway technology. Nowadays, high-speed trains were introduced which has the speed faster than 400 km/h. In Korea, a lots of efforts were undertaken to increase the speed of train faster than 350 km/h, however noise and vibration are still the main problems to solve for realization of the high-speed train. In the case of operation speed faster than 350 km/h, it can be easily presumed that the noise and vibration damages could be increased in the train stations which are close to the passing railway tracks. Thus, the noise in the five different types of high-speed train stations were analyzed including stations built on the ground, underground, under rail, and two types on rail. The present paper predicts noises inside the stations depending on the speed of the passing trains and analyze the noise comparing with noise criteria (NC). Sound insulation performance of each part of buildings was calculated using the transmission noise formula and computer modeling, Finally, a series of processes were introduced to satisfy the aural environment with the optimum interior noise criteria by changing interior finishing materials.

• 재활복지
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• v.22 no.3
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• pp.225-257
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• 2018

The purpose of this study is to find the application point of hearing augmentation technology development through examining the risk context experience of people with hearing impairment and the use of assistive device used as an alternative technology. Data of 355 people with hearing impairment with official disability grading was analyzed. The results of this study are first, research participants had no experience of recognizing any sound or vibration in situations highest in the order of means of transportation, material, and nature. Especially the ratio of being unable to recognize the sound and vibration of means of transportation was high, which implies the high possibility of people with hearing impairment experiencing risk. Secondly, the risk context that people with hearing impairment will most likely to experience are highest in the order of traffic accident, pedestrian accident, and daily life at home. Thirdly, the recognition of 2G phone/smart phone, vibrating digital alarm clock, light bar, vibrating wrist watch as assistive device for risk context awareness and notification was high and the satisfaction level of 2G phone/smart phone was the highest. Fourthly, the research participants had high recognition of assistive device for communication in the order of hearing aid, smart phone, videophone, cochlear implant and 2G phone and it was found that the satisfaction level and communication improvement level was the highest using the smart phone. Lastly, for the development of hearing augmentation technology the research participants recognized the importance of portable/wear convenience, price, and motion accuracy and for notification delivery means they preferred the method of using sight(text and light). Based on the results of this study policy and practical plans for hearing augmentation technology development for people with hearing impairment in risk context are proposed.

• Journal of the Ergonomics Society of Korea
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• v.33 no.1
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• pp.39-48
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• 2014

Objective: This entire study has two parts. Study I aimed to develop a psychological assessment scale and the study II aimed to investigate the effects of LFN (low frequency noise) on the psychological responses in humans, using the scale developed in the study I. Background: LFN is known to have a negative impact on the functioning of humans. The negative impact of LFN can be categorized into two major areas of functioning of humans, physiological and psychological areas of functioning. The physiological impact can cause abnormalities in threshold, balancing and/or vestibular system, cardiovascular system and, hormone changes. Psychological functioning includes cognition, communication, mental health, and annoyance. Method: 182 college students participated in the study I in development of a psychological assessment scale and 42 paid volunteers participated in the study II to measure psychological responses. The LFN stimuli consisted of 12 different pure tones and 12 different 1 octave-band white noises and each stimulus had 4 different frequencies and 3 different sounds pressure levels. Results: We developed the psychological assessment scale consisting of 17 items with 3 dimensions of psychological responses (i.e., perceived physical, perceived physiological, and emotional responses). The main findings of LFN on the responses were as follows: 1. Perceived psychological responses showed a linear relation with SPL (sound pressure level), that is the higher the SPL is, the higher the negative psychological responses were. 2. Psychological responses showed quadric relations with SPL in general. 3. More negative responses at 31.5Hz LFN than those of 63 and 125Hz were reported, which is deemed to be caused by perceived vibration by 31.5Hz. 'Perceived vibration' at 31.5Hz than those of other frequencies of LFN is deemed to have amplified the negative psychological response. Consequently there found different effects of low frequency noise with different frequencies and intensity (SPL) on multiple psychological responses. Conclusion: Three dimensions of psychological responses drawn in regard to this study differed from others in the frequencies and SLP of LFN. Negative psychological responses are deemed to be differently affected by the frequency, SPL of the LFN and 'feel vibration' induced by the LFN. Application: The psychological scale from our study can be applied in quantitative psychological measurement of LFN at home or industrial environment. In addition, it can also help design systems to block LFN to provide optimal conditions if used the study outcome, .i.e., the relations between physical and psychological responses of LFN.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.4
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• pp.299-305
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• 2015

A statistical annoyance model to railway noise at platform was proposed by jury evaluation test performed in hearing laboratory. ITX-Saemaeul and Mugunghwa were chosen as the noise sources of the test, and announcement sound was included to simulate real situation. Logistic regression analysis produced %HA_LAB curve. Hosmer-Lemeshow test and classification accuracy test were used to verify the model's statistical significance. It was shown that the model which was generated from relatively small number of samples is statistically significant.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1177-1182
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• 2007

This study aims at identifying the effect of preferred visual and auditory stimuli on the road traffic noise perception through the series of psychoacoustic experiments. The first experiment was designed to find the addition effect of a sound reproducing system in a square where lay adjacent to roads with road traffic noise, provide appropriate music corresponding to the varying conditions of weather in the given space. In result, it was found that the rating around the square improved toward more positive adjectives. The second experiment was designed to assess the visual effect of twelve roadsides with different landscapes on the road traffic noise perception. As a result, approx. 3 to 5 dB(A) of psychological reduction was seen in places where natural landscape was preferred, compared to the others, although the noise levels were similar. The third experiment was designed to evaluate the effect of visual screen from adjacent roads on road traffic noise perception by means of ME method in a laboratory. In result, the effect of psychological reduction was observed at 65dB(A) or lower. Especially, complete screening from adjacent roads led to 5 to 10% of loudness reduction effect, compared to non-screening cases. Finally, the fourth experiment was designed to evaluate the effect of visual and auditory information with ME method and 7-point SD rating scale in a laboratory. In result, up to 10% of loudness reduction and about 2dB(A) of noise perceptional reduction were seen at 65dB(A) or lower.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.9
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• pp.787-797
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• 2011

The noise in a vehicle is an important factor for customers purchasing a car. Particularly, reduction of the noise that is generated from HVAC(heating, ventilation and air conditioning) is very important since it has considerable effects on interior noise. In general, identification of noise source is crucial to reduce noise level. The complex acoustic intensity method is widely used to obtain the accurate measurement and identification of noise source. Therefore, in the previous study, noise source of HVAC was identified through experimental approach using the complex acoustic intensity method. In this study, we are intended to confirm reduced level of noise by comparing the result between before and after modification of cam curve that is based on identified noise source of HVAC. It is found out that noise source of HVAC are motor and cam area using the complex acoustic intensity method in the previous study. We performed experiments to compare noise level between before and after modification of cam curve. Especially, it can be seen that complex acoustic intensity method using both active and reactive intensity is vital in devising a strategy for comparison to noise level. Also, the vector flow of acoustic intensity was investigated to identify sound intensity distributions and energy flow in the near field of HVAC.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.217-222
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• 2006

Internal combustion engine is the main source of environmental pollutants and therefore advanced technology is required to reduce harmful elements from the exhaust gases all over the world. Especially, when the exhaust gas is released front the automotive muffler, exhaust noise has many bad influence on the surrounding environment. In order to reduce the exhaust noise, it is necessary that automotive muffler must be designed for best exhaust efficiency. The sound insulation room was installed for the analysis of an acoustics characteristics of the noise from automotive muffler, in this study. Exhaust gas noise, noise distribution characteristics, pressure and temperature of exhaust gas were investigated with the change of annulus temperature of air cooled annulus automotive muffler and cooled annulus automotive muffler. The following results were obtained with this study. From the frequency analysis of automotive muffler, high noise distribution was observed in the range $100{\sim}2000Hz$. It means that the noise in this range has an dominate influence for the overall noise. Noise reduction of automotive muffler was affected by the temperature of annulus. It is caused the result that the high temperature and pressure of exhaust gas are changed lower by the drop of annulus temperature. The tendencies of noise, the temperature and pressure of exhaust gas are similar to the performance curve of engine. Exhaust gas pressure is determined by the r.p.m. of engine and affected by the cooling performance of automotive muffler.

• Journal of the Korean Wood Science and Technology
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• v.13 no.3
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• pp.34-40
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• 1985

The characteristics of Paulownia coreana wood used for sounding boards has been revealed through this study. The 80 specimens were selected from Paulownia coreana wood. The dynamic Young's modulus, the internal friction and resonant frequency of wood were measured by the method of making a rectangular bar resonate in the audio frequency range. The results obtained are summarized as follows: 1. The average values of the specific gravity, the dynamic Young's modulus and the internal friction concerning Paulownia coreana used for sounding boards are $0.252{\pm}0.022$, $(0.494{\pm}0.068){\times}10^{11}$ dyne/cm and $(7.89{\pm}1.692){\times}10^{-3}$ respectively. 2. The average values of resonant frequency, the velosity of sound, and K values are $504{\pm}24.298$ Hz, $5018{\pm}219.83$m/s, and $(9.907{\pm}2.05){\times}10^{-4}$ respectively. 3. The dynamic Young's modulus of Paulownia coreana increases with the increase of the specific gravity, and that on the contrary the internal friction decreases. 4. The dynamic Young's modulus was abruptly decreased as the moisture content of wood specimens was increased up to the fiber saturation point, and the internal friction was linearly increased as the moisture content of wood specimens were increased. 5. The vibration properties of Paulownia coreana are that the dynamic Young's modulus is fairly high, the internal friction is low, and the ratio of Young's modulus to specific gravity shows large value.