• 대한조선학회논문집
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• 제48권6호
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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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• 제19권1E호
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• pp.13-21
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• 2000

In this paper, we present the description and results of experimental study of the sound power measurements based on International Standards ISO 3741 and 3745. The sound power emitted by a calibrated reference sound source was measured in a reverberation room and a free field over a reflecting plane, using the precision methods of International Standards ISO 3741 direct method and ISO 3745, respectively. The sound power measurements carried out in this study give accurate estimation and also show that both methods for determining the sound power levels of a sound source in a reverberation room and a free field over a reflecting plane, according to the ISO 3741 and 3745, respectively, have proved equally good.

• Journal of Mechanical Science and Technology
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• 제17권4호
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• pp.511-520
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• 2003

In room acoustics, reverberation time is an important acoustic parameter. However it is often difficult to measure short reverberation times at low frequencies with a traditional band pass filter bank if the product of filter bandwidth (B) and reverberation time (T) is small. It it well known that the minimum permissible product of bandwidth and reverberation time of the traditional band pass filter is at least 16. This strict requirement makes it difficult to measure short reverberation times of an acoustic room at low frequencies exactly. In order to reduce this strict requirement, in the previous paper, the wavelet filter bank was developed and the minimum permissible product of bandwidth and reverberation time was replaced with 4. In the present paper it is demonstrated how the short reverberation times of an practical room at low frequencies are successfully measured by using the wavelet filter bank and the results are compared with the traditional method using a band past filer bank.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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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.

• 한국소음진동공학회논문집
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• 제17권5호
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• pp.373-378
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• 2007

Today, the use of the sound absorptive material is increasing to improve the room acoustics in the auditorium and music hall, etc. Usually, the sound absorption materials have been used to enhance the performance of a noise barrier and improve the room acoustics in construction site. Generally, the sound absorbtion coefficients are the most important factor reflecting the sound absorbtion performance. There are two methods to measure the sound absorption coefficient. The first one is the reverberation room method, and the second is the impedance tube method. In this study, we measure the sound absorbtion coefficients using these two methods, and then we compared the results of the sound absorbtion coefficients to look into the difference of results between reverberation room method and impedance tube method. Also we compared the results of the sound absorbtion coefficients with respect to the size of sample and the volume of reverberation room. From the experiment, we could see that the sound absorbtion coefficients are measured equally for different sample size. But the sound absorbtion coefficients are measured differently according to test methods and test conditions.

• 한국음향학회지
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• 제8권5호
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• pp.59-69
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• 1989

• 한국음향학회지
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• 제22권1호
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• pp.7-13
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• 2003

컴퓨터에 의한 실내음향 예측에 있어 확산반사의 고려는 매우 중요한 요소의 하나로 간주된다. 지난 수년동안 음선추적법과 빔추적법에서 확산반사를 고려하기 위한 방안들이 활발하게 연구되었으나 경면반사를 근본으로 하는 영상법에서는 아직 충분한 연구가 이루어지지 않고 있다. 부분적으로 확산성을 갖는 반사면에서의 음향에너지 반사는 확산반사와 경면반사의 형태로 나누어 볼 수 있으며 반사를 거듭함에 따라 확산-확산, 확산-경면, 경면-확산, 경면-경면의 형태로 반사에너지의 전환이 이루어진다. 본 연구에서는 실내의 벽면을 부분적으로 확산반사의 특성을 갖는 반사면으로 모델링하여 경면반사음은 기존의 영상법으로 계산하고 확산반사음은 라디오시티법을 적용하여 산출하는 확장라디오시티법을 도입하였다. 본 논문에서는 확장라디오시티법의 개념과 이에 따른 고차형태계수의 계산법을 제시하고 고차형태계수가 실내음향 시뮬레이션의 결과에 미치는 영향 등을 분석해 보았다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.216-220
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• 2007

By virtue of recent economic development and cultural progress, the desires willing to enjoy a plentiful leisure life among people are on enlarging, then according to this, the demand for a grand performance hall where various cultural events are achievable is also on increasing. However, since the grand performance hall has its characteristics that must accommodate various forms of performances likely from lecture, meeting activity to recital, and because the clearness of sound is on emphasizing, and also it requires the repletion or abundance of sound simultaneously, it could be said that from the designing stage, a sufficient examination and plan with regard to the architectural acoustics design is indispensable. On such view point, for the object of the grand performance hall under actually planning to build, this Study is attempting to compare analyze on Room Acoustics Characteristics using computer simulation from the stage of design. It is considered that the material analyzed in such way could be reflected in maximum basis to the design of the performance hall that minimizes the acoustic defect at the designing step, and also it could be utilized as the useful material at the time of design for a similar form of performance hall in the future.

• 교육시설 논문지
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• 제18권5호
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• pp.3-11
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• 2011

In this study, the effect of treating 1-dimensional diffusers on the classroom acoustics was investigated to determine if the diffuser are beneficial for performing the preferred acoustical conditions for speech. A 1/10 scale model of a classroom was used to measure the acoustical parameters, T30, $C_{50}$, STI and SNR in that room. The room acoustical conditions were varied by treating diffusers either on the front or side walls of the classroom. When the diffusers were treated on the side walls around the student's areas, a shorter reverberation time at low frequencies was obtained and resulted in performing uniform reverberation times across the frequency bands. The $C_{50}$ values at mid- and high-frequencies were increased by treating the diffusers either on front or side wall surfaces. The highest STI and SNR values were obtained when the diffuser was treated on the front wall around the teacher's areas. It is found that diffusers are beneficial to increase the intelligibility of speech for the rear seats of the rooms.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.253-257
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• 2007

In case of the hydraulic turbine dynamo room at Dam, due to its big volume and reflexible finishing material, since the noise of electricity-generation is amplifying, it influences the difficulty of mutual communication among the workers, also it is causing both mental and physical damages to those workers in the neighboring office. Accordingly, after presentation of the optimized renovation model of the hydraulic turbine dynamo room using the acoustic simulation, this Research has compared and evaluated them using the auralizational technique between the present condition of "before improvement" and the acoustic condition of "after improvement". As the result of psycho-acoustics experiment, as the acoustic conditions at both "before & after Improvement" were apparently compared, it appeared that there is a considerable amount of noise-reduction effect at psycho-acoustics. It is considered that such material could be utilized as the valuable data hereafter for the time when any construction and renovation of the hydraulic turbine dynamo room and other similar workshop.