The Effect Of Sound-field Amplification System On The Chinese Speech Intelligibility In Elementary School Classroom

The elementary school classroom is the primary place to acquire knowledge for children, a good classroom acoustic environment is very important to ensure good speech communication between teachers and students. The subjective Chinese speech intelligibility evaluation and objective acoustical measurement in 28 elementary school classrooms were performed by children in grades 2, 4 and 6 from 9 different elementary schools in Guangzhou. The relationships between %Alcons and subjective Chinese speech intelligibility scores were explored for grades 2, 4 and 6 children respectively. With and without the sound-field amplification system, the sound signals during the class in the 48 classrooms of grades 1~6 from 3 different elementary schools in Guangzhou were recorded, the speech pressure level, the interference noise pressure level and signal-to-noise ratio(SNR) in classrooms were obtained from the recorded signal. With and without the sound-field amplification system in classrooms, the subjective Chinese speech intelligibility evaluation and objective acoustical measurement were performed in 3 elementary school classrooms with different reverberation time(T30) by different grade students. The effect of sound-field amplification system on the Chinese speech intelligibility in elementary school classrooms was explored.The noise pressure level at the seats located in the front and back of the classroom were approximate under using and no using the sound-field amplification system condition, the difference of speech pressure level at the seats located in the front and back of the classroom was significant but less than 6 d B, and the difference in SNR was in the range of 5d B. Regardless of whether the sound-field amplification system was used or not in the classroom, the noise pressure level, speech pressure level and SNR averagely increased with the increase of the age. When the sound-field amplification system was not used, the speech pressure level ranged from 57.4d BA to 80.6d BA and the average speech pressure level was 71.4d BA, but when the sound-field amplification system was used, the speech pressure level ranged from 61.7d BA to 86.2d BA and the average speech pressure level was 77.8d BA. The average SNR were 8.6d BA, 12.3d BA under with and without sound-field amplification system respectively. An increase of approximately 6d B in the speech pressure level and approximately 4d B in the SNR when the sound-field amplification system was used than not used. The correlation coefficient between the noise pressure level and speech pressure level in the classroom was 0.848 when the sound-field amplification system was not used, but there is lower correlation between the noise pressure level and speech pressure level when the sound-field amplification system was used.There were high correlations between subjective Chinese speech intelligibility scores and %Alcons for grades 2, 4, and 6 respectively. The Chinese speech intelligibility scores among different age groups were decreasing with the increase of %Alcons. The Chinese speech intelligibility scores increased with the age increasing under the same %Alcons conditions. To obtain the 95% Chinese speech intelligibility scores, the %Alcons required by the grades 2, 4, and 6 were 2.5%, 4.4%, 5.8% respectively. When the SNR was in the range of 20 ~ 25 d B and the T30 was between 0.4s and 0.8s, the sound-field amplification system was unnecessary for grades 4 and 6 children but necessary for grade 2 children to improve speech intelligibility in the classrooms.Under the approximately 50 d BA natural background noise condition, there was no significant difference(P>0.05) between the subjective Chinese speech intelligibility scores when the speech pressure level at the listening position was approximately 65 d BA with the sound-field amplification system and when the speech pressure level at the listening position was approximately 60 d BA without the sound-field amplification system. Under the approximately 60 d BA speech-shaped interference noise condition, there was significant difference(P<0.05) between the subjective Chinese speech intelligibility scores when the speech pressure level at the listening position was approximately 75 d BA and 70 d BA with the sound-field amplification system, and 65 d BA without the sound-field amplification system, respectively. But there was no significant difference(P>0.05) between the subjective Chinese speech intelligibility scores when the speech pressure level at the listening position was approximately 70 d BA with the sound-field amplification system and 65 d BA without the sound-field amplification system. Regardless of whether the sound-field amplification system was used or not, the higher the SNR at the listening position is, the older children’s age is, and the higher the subject Chinese speech intelligibility scores are. When SNR was lower, using the sound-field amplification system did not significantly improve speech intelligibility in classroom.