• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.7
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• pp.626-633
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• 2012

In this paper, sound pressure sensitivity of the fiber optic acoustic sensor according to sensor direction and mandrel material were investigated experimentally. Three different directions were selected as stand, lay, and hole. Hollow cylinder type mandrel dimension is 30 mm in outer diameter, 45 mm in length, and 2 mm in thickness, and about 50 m optical fibers were wounded on the surface of the mandrel. Non-directional sound speaker was used as a sound source. Sagnac interferometer and single mode fiber, a laser with 1,550 nm in wavelength, $2{\times}2$ coupler were used. Based on the experimental results, lay direction's sensitivity is the highest in the frequency range of 2 kHz~4 kHz. 'PTFE+carbon' material is more sensitive than PTFE in the frequency range of 5 kHz~20 kHz. Sound pressure detection sensitivity depends on the mandrel direction and material under certain frequency.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.18 no.3
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• pp.266-270
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• 1985

In order to obtain the fishing possibility by acoustic, the two fishes, Lateolabrax japonicus, Mugil cephalus, were bred in a water tank. The feeding sounds from the fishes and the artificial sounds were recorded by a hydrophone and then the frequency and the sound pressure level of the sounds recorded were analyzed by the digital frequency analyzer. These sounds were edited in two manners of which one is emitted for 10 seconds and paused for 10 seconds continuously and the other is emitted for 20 seconds and paused for 20 seconds also. These edited sounds were emitted again into the tank and the respose of fisher were observed. Lateolebrax japonicus showed a positive response and Mugil cephalus responsed a little positively to the emitted feeding sound, The fishes seemed to show a positive response only in emitting a moderate pressure level of feeding sound. Lateolabrax japonicus and Mugil cephalus showed negative response to the emitted artificial sound. It was most effective to increase the sound pressure level that the fishes went away from the sound source to the emitted artificial sound.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.5
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• pp.414-422
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• 2013

As structure-borne sound, the floor impact sound is one of the serious noises in residential building. Most of heating system applied to the typical Korean residential building is floor heating system which is called ondol. The ondol usually consists of finishing material, mortar with heating coil, light-weight aerated concrete and reinforced concrete. This study focused on the isolation of heavy-weight impact sound and modification of mortar and light-weight aerated concrete. Specifically the glass foam aggregate was added on light-weight aerated concrete. Also, water-cement ratio and amount of cement on mortar were revised. The sound pressure level of heavy-weight impact was measured in reverberation chamber using both bang-machine and impact ball. The size of specimen was 1 m by 1 m. Substitution ratio of glass foam aggregate on light-weight aerated concrete shows relationship with heavy-weight impact sound pressure level. In addition, heavy-weight impact sound pressure level was decreased with increment of water-cement ratio and amount of cement on mortar.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.11
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• pp.1059-1066
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• 2011

The micro-perforated panel absorber(MPPA) is one of promising noise control elements because of its applicability to extreme environments where general porous materials cannot be used. Since the MPPA is inherently non-porous sound absorber, it can be a good candidate of acoustic protection system of a space launcher. The overall sound pressure level inside payload fairings of commercial launch vehicles is so high(around 140 dB OASPL) that the conventional linear impedance model cannot be directly applied to the design of the acoustic protection systems. In this paper an acoustic impedance models of a micro-perforated panel absorber at high sound pressure environment were reviewed and the use of the impedance on the practical design of MPPAs was addressed. The variation of absorption characteristics of MPPA was discussed according to the design parameters, e.g., perforation ratio, the minute hole diameter, the thickness of MPP and the incident sound pressure level.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.178-185
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• 2011

The micro-perforated panel absorber (MPPA) is one of promising noise control elements because of its applicability to extreme environments where general porous materials cannot be used. Since the MPPA is inherently non-porous sound absorber, it can be a good candidate of acoustic protection system of a space launcher. The overall sound pressure level inside payload fairings of commercial launch vehicles is so high (around 140 dB OASPL) that the conventional linear impedance model cannot be directly applied to the design of the acoustic protection systems. In this paper an acoustic impedance models of a micro-perforated panel absorber at high sound pressure environment were reviewed and the use of the impedance on the practical design of MPPAs was addressed. The variation of absorption characteristics of MPPA was discussed according to the design parameters, e.g., perforation ratio, the minute hole diameter, the thickness of MPP and the incident sound pressure level.

• The Journal of the Acoustical Society of Korea
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• v.31 no.5
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• pp.273-279
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• 2012

In this thesis, a nonlinear compression fitting method was studied for each frequency channel of a 64 channel digital hearing aid. Unlike conventional fitting formula method done from the result of the hearing loss test, the present fitting method uses the auditory threshold of sound pressure measured near the tympanic membrane while ITE (In-The-Ear) hearing aid is fitted into the user's ear canal. Also, the spectral distribution of the voice sound pressure was used for realizing of output sound pressure compression curves against input sound pressure level. Theoretical research results of FFT-iFFT compression algorithm has been evaluated by experimental gain measurements at each different input sound pressure level 50 dB, 70 dB, 90 dB respectively.

• Journal of the Korean Society of Visualization
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• v.22 no.2
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• pp.55-62
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• 2024

Using an internal flow noise test bench, this study investigates the variation in internal flow noise at the inlet and outlet monitoring points of a DN100 T-junction pipe under different flow velocities. Results indicate that with increasing flow velocity, both the sound pressure level and total sound pressure level at the inlet and outlet monitoring points increase. The highest total sound pressure level is observed at the vertical outlet monitoring point B, followed by the horizontal inlet monitoring point A, with the lowest at the horizontal outlet monitoring point C. At a constant flow velocity, the sound pressure level at the inlet and outlet points initially increases and then decreases as frequency increases.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.3
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• pp.36-43
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• 1997

In order to make unmanned machining systems with satisfactory performances, it is necessary to incorporate appropriate condition monitoring systems in the machining workstations to provide the required intelligence of the expert. This paper deals with condition monitoring for tool wear and breakage during turning operation. Developing economic sensing and identification methods for turning processes, sound pressure measurement and digital signal processing technique are proposed. The validity of the proposed system is confirmed through the large number of cutting tests.

• The Journal of the Acoustical Society of Korea
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• v.25 no.1E
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• pp.25-31
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• 2006

Two twin microphones may produce particular patterns of binaural directivity by time delays between the twin microphones. The boundary element method (BEM) was used for the simulation of the sound pressure field around the KEMAR head model in order to quantify the acoustic head effect. The sound pressure onto the microphone was calculated by the BEM to an incident sound pressure. Then a planar directivity pattern was formed by four sound pressure signals from four microphones. The optimal binaural directivity pattern may be achieved by adjusting time delays at each frequency while maintaining the forward beam pattern is relatively bigger than the backward beam pattern. The simulation results were verified by the experimental measurement.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.742-742
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• 2003

This study is about the effect of the sound pressure level of reverberation on stage acoustics. There are several electro-acoustics systems to enhance the room acoustics of concert hails but not many studies on the stage acoustics for the musicians who plays on the stages. To investigate the effect of reverberation on stage acoustics, the reverberation time of a test room has been controlled through a 4 channel speaker system, and the preferred reverberation level has been selected by performing musicians. As a result, the sound pressure level of reverberation seems to affect the perception of stage acoustics which motivates musicians' performances.