A Survey Of Acoustic Conditions,Problems And Solutions In Primary And Secondary School Classrooms

The acoustic environment of school buildings directly affects the quality of teaching and learning.Poor acoustic environment of classrooms affects not only the cognitive ability and academic performance of students,but also the fatigue degree and throat health of teachers.The auditory system of children and adolescents is unmatured,and the speech recognition ability of children is significantly worse than that of adults.Therefore,it is very important to create a classroom acoustic environment suitable for children and adolescents.First,in order to understand the current acoustic environment situation of ordinary classrooms in primary and secondary schools in China,this project takes 30 pr imary and secondary school classrooms in Guangdong,Guangxi and Fujian provinces as objects to carry out acoustic survey.The research sample covers ordinary classrooms in primary schools,middle schools and high schools.The acoustic survey includes the school and classroom building parameters survey,subjective questionnaire survey,and the measurement of important objective acoustic parameters in classrooms,such as reverberation time and indoor noise level in unoccupied classrooms,outdoor noise level,airborne sound insulation between rooms,noise level in occupied classrooms,and indoor sound level when teaching,etc.This work is more comprehensive,systematic and fundamental than the previous domestic research.The survey results show that due to the lack of reasonable classroom acoustic design and sound insulation and noise reduction measures,there is more noise sources in the classrooms,and the noise level is high,which cannot ensure that all students can clearly hear the voice of teachers,and a certain number of teachers and students are dissatisfied with the classroom acoustic environment.In addition,both subjective and objective research results show that it is a common phenomenon that teachers need to increase the volume to teach（the indoor sound level during teaching ranges from 63.6 d B A to 79.3 d B A,with an average of 70.8d BA）.The range of reverberation time in the 30 unoc cupied classrooms is 0.63～1.85s.The range of indoor noise level under three measurement conditions（unoccupied,occupied and teaching+occupied）is 41.9～84.9d BA.The range of sound insulation between ordinary classrooms is 33～47 d B.For 77%and 69%of the surveyed classrooms respectively,the reverberation time and the sound insulation between rooms cannot meet the limit requirements in GB 50118-2010 Code for Design of Sound Insulation of Civil Buildings.Under the measurement conditions required by this code,the indoor noise level of all unoccupied classrooms cannot meet the limit requirements.Because of no sound absorption treatment,the reverberation time of most surveyed classrooms is too long.The deficient sound insulation performance of the classrooms also makes the indoor noise level generally too high.Based on the above main problems of the acoustic environment in ordinary classrooms of primary and secondary schools,the relationship between subjective speech intelligibility score and objective acoustic parameters is investigated by means of subjective assessment experiments of speech intelligibility.The experiments,including those under the real sound field conditions in the classroom scene and those under different sound field conditions simulated by auralization techniques,take primary school students as subjectives and investigate the applicability of different experimental methods.The results show that the current national standard GB/T 15508-1995 Acoustics-Speech Articulation Testing Method is not applicable to primary school students.In this study,the subjective evaluation methods in the above standard is optimized for the first time.Retelling is used to replace handwritten records,and an improved KXY syllable table method is proposed for the subjective evaluation of speech intelligibility of primary school students.With this method,the correlations between speech intelligibility score and beneficial/harmful sound energy ratio U₅₀ and speech articulation index STI are obtained.For students in grade 4/5,the required U_{50（500-4k Hz）}and STI are 3.4 d B and 0.68,respectively,to achieve 100%speech intelligibility.Besides,U_{50（500-4k Hz）}is proposed as a more practical parameter for evaluating the speech intelligibility of occupied classrooms.Second,a standardized typical classroom model is established,and the optimization design strategies of acoustic environment that meets the basic requirements of the Code for Sound Insulation Design of Civil Buildings is proposed.The computer simulation technology is used for prediction.To meet the limit requirement of reverberation tim≤0e.8s or 1s,thesuggested design scheme of sound absorbing materials in classrooms is given.In order to meet the limit requirement of indoor noise level≤45d BA,this study uses the numerical calculation method to estimate the required air sound insulation of the external window.Finally,this study proposes adopting U_{50（500-4k Hz）}in occupied classroom as the evaluation parameter when a higher sound quality of the classroom is required.In order to meet the requirement that students can achieve 100%speech intelligibility when teachers teach with normal volume,this study provides advices on the optimization design of the classroom acoustic environment.The above research outcomes can supplement and expand the acoustic environment research work,and provide basis and reference for the establishment of acoustic design specifications for primary and secondary schools in China.