• Korean Journal of Fisheries and Aquatic Sciences
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• v.44 no.5
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• pp.543-549
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• 2011

An underwater speaker was developed for use as an acoustic deterrent device that transmits acoustic energy through the water omnidirectionally over a broadband frequency range to eliminate marine mammal attacks and to prevent physical damage to the inshore and coastal fishing grounds of Korea. The underwater speaker was constructed of two vibration caps machined from 6061-T6 aluminum alloy and a stack of PZ 26 piezoelectric ceramic rings (Ferroperm Piezoceramics A/S) connected mechanically in series and electrically in parallel. The performance characteristics of the underwater speaker were measured and analyzed in an experimental water tank of $5\;m{\times}5\;m{\times}6\;m$. The peak transmitting voltage response (TVR) was measured at 11.16 kHz with 163.45 dB re $1\;{\mu}Pa$/V at 1m. The underwater speaker showed a near omnidirectional beam pattern at the peak TVR resonance frequency. The usable frequency range was 4-25 kHz with a lower TVR limit of approximately 140 dB. We conclude that this underwater speaker could be satisfactorily used as an acoustic deterrent device against marine mammals, particularly the bottlenose dolphin, to protect catches and fishing grounds as well as the mammals themselves, for example, by keeping them away from fishing gear and/or vessels.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.62 no.4
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• pp.192-197
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• 2013

Road traffic noise barriers being used to reduce the noise, but the city surroundings inhibition, ecosystem disturbance, and it is difficult to maintain. Can enhance or complement the existing noise barrier performance, so that it is necessary to develop an electronic noise-reduction system In this paper, we proposed an electronic road noise reduction devices to reduce road noise for a DSP-based signal processing and analog signal input-output controller. In order to verify the control performance, we performed noise reduction experimentation of ANC by filtered-X LMS algorithm and traffic noise signal injection. The controller is equipped with noise reduction algorithms were tested on the characteristics of directional and omnidirectional speaker.

• Proceeding of Spring/Autumn Annual Conference of KHA
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• 2004.11a
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• pp.361-366
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• 2004

This study has carried out in order to furnish the fundamental material to systemize the lecture room into multimedia in the future, by locating college lecture room as the subject of study, by compare and analyze on acoustic character in both before and after of each improvement. Thereby, now we are about to compare and analyze on physical character of room acoustics in both common lecture room before improvement and the modified multimedia-lecture room after its improvement. Observing the conclusion obtained through experiment, reverberation time in the modified 'lecture room after improvement' became shorter compare with the 'lecture room before improvement', definition and RASTI also improved to be suitable to lecture, and considered that it is able to elevate the intimacy with studying and teaching efficiency, as well.

• Proceeding of Spring/Autumn Annual Conference of KHA
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• 2004.11a
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• pp.367-371
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• 2004

The purpose of this research is furnishing of basic material for acoustic planning hereafter, after understanding the acoustic merits and demerits through measuring and analyzing on room acoustic of small performance hall. As the result of the measurement, those physical evaluation indexes such as SPL, RT, EDT, $D_{50}$, $C_{80}$, RASTI have being kept the satisfiable acoustic condition for the service of performance hall. Therefore, as small performance hall is regarded as equipped with sufficient volume of sound, reverberatory feeling and diffusive feeling, it judges as an excellent performance place, also it is considered that it could be utilized as a useful material when design so similar performance hall, hereafter.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.268-272
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• 2007

As Music Room in Art School is mainly for exercise of musical instrument rather than any lecture or music appreciation, it should be designed and constructed in consideration with Acoustic Condition on the preferential basis. However, in case of Music Room in Art School that has been built already or latest newly constructed, since it was designed and constructed without any reflection of Acoustic Characteristics, it appeared as inadequate for them to enjoy music appreciation or performance activity. On such view point, this Study has examined the physical Acoustic Characteristics for the subjects on those Music Rooms of Art Middle School, Art High School, Art College built in Cheonbuk Province, and it is deemed that the material grasped in such way could be utilized as the valuable data enables to improve Acoustic Performance at the time when designing and construction or renovation for Music Room hereafter.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.5
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• pp.429-436
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• 2012

In concert halls and auditoriums, acoustic reflector and stage enclosure is one of the main factors on the room and stage acoustic characteristics. As a stage enclosure and acoustic reflector honey comb based light-weight reflector is widely used, because it is easy to install. However, there was not enough research on the surface density effect on room and stage acoustics. In this study, sound absorption coefficient tests on three kinds of wooden acoustic reflectors with different surface density were conducted. Surface density of acoustic reflector was changed from 11 kg/$m^2$ to 41 kg/$m^2$. For the low frequency excitation, sub-woofer was used with omnidirectional loud-speaker simultaneously. From the experiments, it was found that sound absorption coefficient below 250 Hz band was decrease by the increment of surface density. In order to check the influence of the surface density on room and stage acoustic parameters, room acoustic simulation was conducted with sound absorption coefficients, which were tested in reverberation chamber. By the increment of surface density of acoustic reflector, RT(reverberation time) and EDT(early decay time) were increased. Also, ST(stage support) was improved in low frequency bands.