Assessment of speech intelligibility during different teaching activities in classrooms with and without acoustic treatment

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Elsevier Ltd

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There is limited data for assessing speech intelligibility in real classrooms with realistic occupied noise levels and teacher's and students’ speech levels for different teaching activities in Turkish secondary school classrooms. This study investigates the effect of reverberation time (RT), occupied noise levels and signal-to-noise ratio (SNR) on speech transmission index (STI) in real classrooms for instruction and group work. Noise levels were measured and STI values were calculated in two secondary school classrooms with RT of 0.88 s and 2.73 s. During instruction situation, calculated mean STI values were 0.63 (classroom with acoustic treatment) and 0.29 (classroom without acoustic treatment) for normal voice effort and 0.65 (classroom with acoustic treatment) and 0.39 (classroom without acoustic treatment) for raised voice effort. During group work, STI values ranged from 0.50 to 0.74 in classroom with acoustic treatment and from 0.01 to 0.34 in classroom without any acoustic treatment. SNR of 15 dBA is only approached in classroom with acoustic treatment during instruction situation. The effect of increasing SNR on STI is prominent in the classroom without acoustic treatment which already has low SNR values. The present results show that the classroom with acoustic treatment will have good speech intelligibility for instruction with normal vocal effort and for group work with raised vocal effort at 3 m distance. However, the classroom with no acoustic treatment will have STI values in the range of bad and poor intelligibility. The present results confirm the impact of SNR and RT on speech intelligibility and shows that RT value of minimum 0.8 s is optimal to have good speech intelligibility in a secondary school classroom of approximately 250 m3 with a capacity of 18 students.


This study was supported within the scope of The Scientific and Research Council of Turkey-1001 Research Grant Scheme under Project No. (114K738) and Project Title of “Noise Pollution in School: Causes, Effects, and its Control”. The authors would like to thank Prof. Dr. Ali Yurdun Orbak for his valuable contribution during the measurements in the school without acoustic treatment.

Anahtar Kelimeler

Classroom acoustics, Secondary school classrooms, Signal-to-noise ratio, Speech intelligibility, Speech transmission index, Acoustic noise, Architectural acoustics, Reverberation, Speech communication, Speech transmission, Students, Acoustic treatment, Group work, Index values, Noise levels, Reverberation time, Secondary school classroom, Secondary schools, Teaching activities, Signal to noise ratio, Primary-school teachers, Room acoustics, Normal-hearing, Perception, Parameters, Design, Discrimination, Recognition


Applied Acoustics

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Şaher, K., Bulunuz, M., Kelmendi, J. & Nas, S. (2023). Assessment of speech intelligibility during different teaching activities in classrooms with and without acoustic treatment. Applied Acoustics, 207, 1-18. doi:10.1016/j.apacoust.2023.109346