The most important function of the classroom is to transmit educational information from teachers to students more accurately and clearly. And it is closely related to acoustical environment of the classroom.
Acoustical environment of the classroom, ...
The most important function of the classroom is to transmit educational information from teachers to students more accurately and clearly. And it is closely related to acoustical environment of the classroom.
Acoustical environment of the classroom, thus, has an important effect on the improvement of students' learning ability. Especially, short reverberation time, high clarity, and silent environment elevate students' speech perceptional performance and thus play a large role in improving their learning ability.
To provide appropriate uniformly acoustical environment for learning to students, it is necessary to make acoustical performance criteria for classrooms and a guideline for designing classrooms. For now, in America, England, and etc., there is acoustic performance criteria for classrooms based on reverberation time and background noise. And it is strictly applied when new constructing or reconstructing the school. However, in Korea, there is no acoustical performance criteria for classrooms, so it is difficult to control and manage appropriate acoustical performance when designing classrooms.
In this study, therefore, suggests acoustic performance criteria for classrooms in Korea, to provide students appropriate uniformly acoustical environment for studying. The subject of the research was middle and high school classrooms, and it measured acoustical performance at classrooms in Cheongju, to know their actual acoustical environment. It also tested speech intelligibility of Korean, English and Chinese, to know differences of speech perceptional performance among students, when they are learning other languages including Korean. In addition, it investigated and examined proper location of sound absorbing material for controlling reverberation time when designing classrooms. Finally, it established appropriate reverberation time criteria for middle school and high school classrooms in order to make students recognize educational information clearly, by testing their speech intelligibility under different reverberation time.
The findings of this research are summarized as allows:
1) An experiment was performed to know the actual acoustical performance at middle school classrooms in Cheongju. It proved that background noise in some classrooms exceeded 35dB(A), which is acoustical performance criteria for classrooms in America and England. As for reverberation time, almost classrooms except just one exceeded 0.6 sec, which are the criteria of America. Even some of them exceeded 0.8 sec, the criteria of England.
2) As for differences of speech intelligibility according to languages at classrooms, English and Chinese got higher scores than Korean under the same reverberation time. And there is a meaningful correlation between every language and D50 and early reflected sound. It means that early reflected sound has much influence on language information transmission. On the other hand, there is higher negative correlation between reverberation time and Chinese and English except Korean. It proved that each language has different factors to improve its clarity. Therefore, acoustical criteria for Korean classroom is certainly needed, which is appropriate for its communication features.
3) It also studied the relationship between the location and students' speech perceptional performance, when sound absorbing material is set up in order to control reverberation time. When measuring acoustical performance before and after setting up sound absorbing material, inter-aural level difference(ILD) were larger, as closer to sound absorbing material on side walls. And when correlation between ILD and improvement ratio of speech intelligibility was investigated, a correlation coefficient value R was -0.441. It proved that both factors have meaningful negative correlation. It means that students' speech intelligibility becomes decreased as ILD becomes larger because of sound absorption performance of finishing materials.
4) It investigated and revealed appropriate reverberation time for middle and high school students' learning. To achieve this, standard classrooms were made by standardizing architectural dimension of 17 classrooms in Cheongju. After that, auralized sound source was made under 5-step conditions of reverberation time(0.47 sec ~ 1.22 sec) by changing indoor sound absorption of classrooms. A listening test on 52 adults with normal hearing, using the auralized sound source, proved that the most appropriate reverberation time for learning was above 0.76 sec.
5) Based on the research findings, ideal acoustical performance criteria in Korea is like that : background noise is below 35dB(A), and reverberation time is below 0.80 sec. Also, to meet acoustical performance criteria, it is necessary that indoor sound absorption should be above 20% without sound absorbing material on side walls.
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