• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.176-179
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• 2005

A case-study in classroom acoustics was conducted and the effects of two types(system air conditioner and packaged air conditioner) of air conditioner were investigated. Acoustical measurements were made in two different classrooms. Each classroom has different acoustics showing sound quality of air conditioner. Mental concentration test was conducted to evaluate the effects of air conditioner noise with different sound presure level(dBA). Speech intelligibility test was also planed with adopting Korean phonetic balanced words.

• Journal of the Korean Institute of Educational Facilities
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• v.18 no.5
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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.

• The Journal of the Acoustical Society of Korea
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• v.42 no.2
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• pp.113-123
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• 2023

This paper describes the acoustical conditions of elementary school and high school classrooms as well as university classrooms in Korea and suggests a need for Korean acoustic standards and guidelines for classroom design. Current standards and guidelines of classroom acoustics in several countries were briefly introduced to understand their acoustical performance criteria for background noise levels and reverberation times, and noise isolation design requirements in various types of classrooms. The results of several acoustic survey of domestic classrooms in elementary school, high school, and university were described and compared to provide information of the acoustic characteristics of Korean school classrooms. The survey includes occupied and unoccupied data on the acoustical conditions, noise levels, and noise isolation performance in the classrooms. Acoustical parameter values for achieving 'good' speech intelligibility in active university classrooms were also presented.

• Journal of the Korean Institute of Educational Facilities
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• v.20 no.1
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• pp.37-44
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• 2013

The present study examines the effects of periodic type diffusers for producing the preferred acoustics for speech and determines the more successful configurations of sound-absorbing and diffusing treatments for achieving good acoustics in classrooms. The measurements were carried out in a 1/10 scale model classroom systematically adding diffusers to one or more of four surfaces of the room. A total of 13 combination of diffusers with absorptive treatments were investigated. Adding diffusers on the ceiling were more effective to increasing the early-arriving reflection energy($G_{50}$) than adding absorptive materials on the entire ceiling. The late arriving reflection energy($G_{late}$) was decreased with increasing amounts of diffusing treatments of upper front or rear wall and this resulted in achieving higher early-to-late ratios($G_{50}$). Adding diffusers on the upper front wall($AC_{100}DUFW_{26}$) achieved more uniform acoustical conditions over the receiver positions than adding diffusers on the upper rear wall($AC_{100}DUFW_{26}$). Adding diffusers on the ceiling and absorptive materials on the lower front wall($AC_{75}DC_{25}ALFW_{26}$) achieved better acoustical conditions than adding the absorptive materials on the entire ceiling and lower front wall($AC_{100}ALFW_{26}$).

• Journal of Industrial Technology
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• v.41 no.1
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• pp.15-20
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• 2021

This work proposes a simple method to use the added absorption per person values to predict the expected values of the acoustical conditions in occupied classrooms. This method is based on the effects of the values of added absorption per person on the unoccupied total absorption values of the classrooms and on other room acoustical parameters. The total sound absorption in an unoccupied classroom can be calculated from measured reverberation times in the classroom. The expected occupied absorption can be calculated using equation which was obtained in a previous study (Choi, 2017) by fitting a linear regression line to a plot of total occupied absorption versus the corresponding unoccupied total absorption values measured in 12 university classrooms. The ratios of occupied-to-unoccupied sound absorption are used to predict increments in the values of acoustical parameters that result when occupants are added to the rooms.

• The Journal of the Acoustical Society of Korea
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• v.28 no.2E
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• pp.60-65
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• 2009

The present study aims to investigate the effects of sound diffusers and absorbers on the sound clarity in classrooms. In order to do this, computer simulations were carried out to find the effective area of treatment which could enhance the sound clarity in the room. Acoustic measurements were undertaken in a lecture room with several conditions changing the surface of walls and ceilings with diffusers and absorbers. Diffusion and absorption treatments were applied to the side walls, rear wall and the ceiling of the classroom. SPL, RT, D50, RASTI were measured at 9 measurement points with one sound source and MLS was used as the sound source signal. The results show that higher sound clarity was obtained when diffusers were applied to rear walls and ceiling rather than side walls. Also, it was confirmed that absorption increased sound clarity more effectively with smaller amount in comparison with diffusers. It was also concluded that the effects of sound diffusers and absorbers on the sound clarity could be obtained distinctly at the rear area of the classroom.

• Journal of the Institute of Convergence Signal Processing
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• v.8 no.1
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• pp.32-38
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• 2007

In order to establish the environmental condition of sounds in the classroom, we measured the impulse response in cases of using and not-using PA(Public-Address). By calculating the physical index of acoustics, I examined the differences between the two cases. The degree of improvement in listening with the help of PA has also been studied by testing the voice articulation with the use of the measured impulse response. As a result, I found that the clearness is enhanced by increasing the sound pressure level in the case of short reverberation. However, it was not the case when the reverberation time was long.

• The Journal of the Acoustical Society of Korea
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• v.31 no.3
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• pp.129-141
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• 2012

The present study aims to investigates the effects of the physical sound clarity (D50, STI) on the subjective speech intelligibility of the both Korean and Chinese languages which can be caused by increase of the sound absorption in classroom. In order to this, sound measurements were undertaken at a classroom with and without absorption materials. Also, speech intelligibility tests were conducted by Korean and Chinese students using their native languages. As the results, it was found that both sound clarity and speech intelligibility were improved with increasing sound absorption. Also, it was revealed that Chinese speech intelligibility was more improved than Korean with same impose of sound absorption. It was considered by the difference of phonetic characteristics of two languages. Analysing correlation of physical sound clarity and subjective speech intelligibility, it was shown that D50 is highly correlated with Korean (0.696) and Chinese (0.707) respectively. Also, STI was highly correlated with Korean (0.651) and Chinese (0.665). Thus, it can be concluded that D50 and STI have significant correlations with the speech intelligibility.

• 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.25 no.7
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• pp.462-469
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• 2015

This study was carried out to examine characteristics of various acoustic indicators evaluating speech intelligibility such as reverberation time(T₃₀), D₅₀, C₅₀ and speech transmission index(STI) in Korean elementary school classrooms. Results showed that mean T₃₀ at middle frequencies(500 Hz to 2000 Hz) measured in 9 classrooms was about 0.75 s, which exceeds a regulation specified on American National Standards(ANSI); 0.60 s. Mean D₅₀, C₅₀ and STI were 60 % to 66 %, +2 dB to +3 dB, and 0.65, respectively. The maximum difference in D₅₀ and C₅₀ according to different receiver points in a classroom was 13 % and 2.5 dB, while the maximum difference in T₃₀ was 0.03 s. Whereas STI measured in classrooms has relatively low correlation with other indicators, correlation between D₅₀ and C₅₀ was high, R²=.9964. In addition, T₃₀ and C₅₀ were fitted well as logarithmic regression curve with R²=.9610. It was +3.73 dB in C₅₀ and 68 % in D₅₀ which are the value corresponding to 0.60 s in T₃₀ on this curve.