Initial Study on the Reverberation Time Standard for the Korean Middle and High School Classrooms Using Speech Intelligibility Tests

The most important function of the classroom is to transmit educational information from teachers to students more accurately and clearly. The acoustical environment of the classroom thus has an important effect on the improvement of students' learning ability. To provide an appropriate acoustical environment for learning to students, it is necessary to create an acoustical performance standard for classrooms and a guideline for designing classrooms. However, in Korea, there is not an acoustical standard for classrooms; thus, it is difficult to control and manage appropriate acoustical performance when designing and building classrooms. The present study aims to suggest acoustic performance standards for classrooms that are suitable for the Korean language. In order to perform this study, standard classrooms were created by standardizing architectural dimensions of 17 middle and high school classrooms in Cheong-ju. Speech intelligibility tests were conducted using three different languages including Korean, English, and Chinese. Twenty native speakers for each language were used as subjects for the speech intelligibility tests. Finally, auralized sound sources were created with five different conditions of reverberation time (0.47 similar to 1.22 s) by changing indoor sound absorption of a real classroom. Listening tests were undertaken by 52 Korean adults with normal hearing, using the auralized sound source. The results proved that the most appropriate reverberation time for learning was above 0.76 s. Based on the research findings, the ideal acoustical performance standard for classrooms in Korea is as follows: background noise is below 35 dBA, and reverberation time is below 0.80 s. It is also necessary that indoor sound absorption should be above 20% without sound absorption on side walls in order to satisfy with the acoustical performance standard.