• Korean Journal of Materials Research
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• v.20 no.12
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• pp.640-644
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• 2010

Information technology devices, such as cellular phones, MP3s and so on, due to restrictions of space, require thin and small micro-speakers to generate sound. The reduction of the size of micro-speakers has resulted in the decrease of sound quality, due to such factors as frequency range and sound pressure level. In this study, the acoustical properties of oval microspeakers has been studied as a function of pattern shape on the diaphragm. The other conditions of micro-speakers, except for the pattern, was not changed. When the pattern is present on the diaphragm and the shape of pattern was a whirlwind, the resonance frequency was reduced due to the decrease of tensile strength of diaphragm. The patterns presented in the semi-minor axis of diaphragm did not effect a change of resonance frequency. However, increasing the number of patterns in the semimajor axis of diaphragm became a reason for the decrease of resonance frequency on edge side. When the depth of pattern on edge side was increased, the resonance frequency was decreased due to reduction of geometrical stiffness. If the height of edge and dome were increased, the resonance frequency and geometrical stiffness rapidly increased. After reaching the maximum values, they began to decrease with the continuous increase of height.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.704-709
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• 1998

An automated calibration system of sound level meters was developed and tested. As a standard sound source, the speaker unit(Forstex FE208) cabineted by 440 * 390 * 490 mm$^{3}$(LHW) volume wood box was adopted. Including this source, the driving part was found out to have a good linearity of sound pressure output vs AC input. We use the Hybrid-Bisect, /Newton-Raphson method modified by the linearity as searching algorithm. Personal computer and program do the control, measurements, and calculations and finally do the accumulation of useful data and results. Several trials of automatic calibration using this developed system give reliable results.

• The Journal of the Korea institute of electronic communication sciences
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• v.6 no.5
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• pp.703-708
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• 2011

In this paper, most of the church except for a large church has accommodated many audience to install a balcony floor in a small space. therefore, dead zone and dislocated sound image localization is made due to this under-balcony seats. This paper propose that the problems of dead zone and dislocated sound image localization could be solved using computer simulation in the view of practical side. The economical computer simulation tool, Mapp online that can be found easily was used to the specified church. Installation a sub speaker for dead zone and -10 dB power control of the sub speaker to main speaker power for dislocated sound image localization was proposed. Computer simulation result shows that the value of definition for area was improved from "Normal" to "Very Good" which means about 52% improvement.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.6
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• pp.569-574
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• 2011

In research vessels or naval ships, airborne noise from machineries such as diesel engine is the major source of underwater noise at low speed. In this paper, effect of engine noise on underwater noise is studied by considering two paths; sound radiation from hull plate and direct airborne noise transmission through hull plate. SEA (Statistical energy analysis) is used to predict hull plate vibration induced by engine noise, where SEA model consists of only two subsystems; engine room air space and hull plate. The pressure level in water is calculated from sound radiation by plate. Engine noise transmission through hull plate is obtained by assuming plane wave propagation in air-limp plate-water system. Two effects are combined and compared to the measurement, where speaker is used as a source in engine room and sound pressure levels in engine room and water are measured. The hydrophone is located 1 m away from the hull plate. It is found below 1000 Hz, prediction overestimates underwater sound pressure level by 5 to 12 dB.

• The Journal of the Acoustical Society of Korea
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• v.11 no.2
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• pp.28-37
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• 1992

In the study, the Acoustic transducer of a thin circular disc-type with PZT/Metal was manufactured. The 'tape casting method' was introduced to prepare the thin disc-type of piezoelectric ceramics. The acoustic characteristics of PZT/Metal acoustic transducer for piezoelectric buzzer and piezoelectric speaker etc. have been studied and analyzed. As a result, the sound pressure level (dB), in the range from -6dB to -14dB, increased with increasing the piezoelectric coeffeicient ($d_{31}$) of ceramics. The optimal conditions of the sound pressure characteristics of acoustic transducer were that the radius ratio(${\eta}$) of ceramics and metal plate is 0.7-0.8 and the thickness ratio(${\beta}$) is 1.0, and the value were -15~-165dB.

• Transactions of the Korean Society of Automotive Engineers
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• v.2 no.6
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• pp.29-37
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• 1994

Active noise control of random noise which propatate in the vehicle cabin as a form of spherical wave is the target of this study. In the previous study, the adaptive algorithm for adaptive controller is presented for the application in active noise control system. And for the preliminary study of adaptive active noise control in vehicle cabin as a real system, a computer simulation is performed on the effectiveness of the adaptive algorithm in the amplitude of the pressure fluctuation. This work studies the implementation of multi-channel feedforward adaptive algorithm for the reduction of the noise inside a vehicle cabin using a number of secondary sources derived by adaptive filtering of reference noise source. Multi-channel adaptive feedforward algorithm are verified in numerical simulation and semi-experimental justification of developed system is made on a domestic passenger car. In the results of semi-experimental study, the noise of specific region in the interior of automobile are reduced for the appreciabe sound pressure level in the operating engine rpm and finally this study suggests the capabilities of the real time active noise control in 3 dimensional acoustic fields.

• Fire Science and Engineering
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• v.33 no.1
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• pp.130-137
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• 2019

In this study, the acoustic characteristics of 13 types of emergency broadcasting speakers were tested under the test set-up of UL 2043 and compared. When the sound pressure level of 1 W speakers was compared with speakers with a 15 W output, the SPL of the 15 W speakers was approximately 20 dB higher in some frequency bands. Loudness analysis showed that people can recognize emergency sound from a 15 W speaker twice as loud as the emergency sound from 1 W speakers. The analysis results on the articulation index (room) had an opposite tendency with loudness results, meaning that small speakers can generate clearer sound. Therefore, it is necessary to improve emergency broadcasting speakers to generate louder and clearer sound. Moreover, a performance evaluation standard is needed based on the reasonable and quantitative measurements and evaluations of the acoustic characteristics of the emergency-broadcasting speakers so that a sufficient and clear sound can be generated in various spaces. In addition, it is necessary to establish standards for the clarity of emergency broadcasting in various spaces.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.14 no.2
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• pp.57-62
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• 1978

When fisherman use the boat seine net to catch anchovy, a large noise (drum can, small drum and small gong) is used to scare the anchovy school along the wing nets, and into the bag net were they are caught. We want to know how much of an effect these s:mnds have on forceing the anchovy school towards the bag net. The underwater sounds of ancho\'y, drum can, small drum and small gong were analyzed in the labroatory. The behavioral responeses to the playback sounds of anchovy feeding and sounds of artificial instruments were also investigated. The feeding and artificial sounds of the samples were recorded by a tape recorder through a hydrophone in an anechoic aquarium. The sound intensity level was measured by means of a sound level meter in an anechoic chamber. The frequency and intensity of various sounds were analyzed with an analyzing system consisting of a ~-octave filter set, a high speed level recorder, an amplifier and an oscilloscope. The most successful recording was edited into a 9 to 10 second sound track and was repeated in a sequence of 9 to 10 second intervals. The sequence was then reproduced into an anechoic aquarium through the underwater speaker. The results of investigation are as follows; 1. The frequency of the feeding sound was 63~80Hz, and the pressure level produced was less than 32db. 2. The frequencies of the artificial sounds were 315~ 1,OOOHz, and the pressure levels were 88~95 db in the air. 3. When a hydrophone was placed 70cm below the surface with artificial sounds (drum can, small drum and small gong) produced 1 meter above the surface, the pressure level decreased about 30db. 4. The feeding sound was ineffective in attracting the anchovy, because of interference from ambient noise. 5. The artificial sounds had such a small effect on the anchovy's that they could not be used in ocean fisheries.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.3 s.96
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• pp.320-328
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• 2005

Last target of architectural acoustics is that people wish to convey voice effectively from the space adaptively in use purpose in building. But, how exactly through space sound (sound source) that wish to deliver from indoor can be passed method to do quantification and evaluate quantity of sound by method to serve indoor architectural acoustics estimation summer period and methods to estimate definition propose. This Study searches special quality of sound source about MLS signal that is occurred short-answer sound source (pistol sound source) and nondirectional speaker among indoor sound estimation method, and measure and analyzed reverberation time (RT60), definition (C80, D50) by regulation of each ISO 3382 in age place (classroom, hall, gymnasium). Analysis result and sound factor among could know that d of two sound sources converges in measurement error extent about reverberation time (RT60) of analysis incidental and sound factors and value shows change irregularly about sound factor of D50, C80, pistol sound source judged there is problem. Also, could know that problem is happened in deflection except reverberation time is in deflection analysis with wave that measure each in fixed distance in branch. Finally, when differ size of sound source and measure about change of sound pressure level in case measure sound pressure level giving difference about 10 dB, sound factor could know that there is no different effect.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.2 s.107
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• pp.183-189
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• 2006

In mobile phones of multimedia era, microspeakers of high qualify sound are essential parts to generate human voice in speaker phone and MP3 song player. In this paper, two types of microspeakers, outer permanent magnet (PM) and combined PM type, are analyzed using electromagnetic, mechanical and their coupling analysis. For performance comparison, voice coil diameter is chosen as a design parameter to change excitation position and magnet volume for both types. For combined PM type, sound pressure level (SPL) is improved due to increased PM volume compared to outer PM type. Also, with the decreased voice coil diameter for combined PM type, the 1st resonant mode of the diaphragm is more efficiently excited due to concentrative excitation, resulting in lower and broader frequency range. Therefore, it can be said that the combined PM type microspeakers are more advantageous for high performance microspeaker which are essential for multimedia era.