Study On The Relationship Of Reverberation Time,Background Noise And Speech Transmission Index For Classrooms

The classroom is the main place for teachers to teach and students to learn,and verbal communication is the main teaching method in class.Poor classroom acoustic conditions will directly affect the speech perception of teachers and students.Obtaining good speech intelligibility in the classroom is the main goal of classroom acoustic design.At present,the domestic and international classroom acoustic design standards that guide classroom sound quality design mainly use reverberation time(RT)and background noise as acoustics control indexes,but the correspondence between these two parameters and speech intelligibility is not direct.The objective evaluation parameter of speech intelligibility,speech transmission index(STI),is directly corresponding to the subjective perception of speech intelligibility,but it is not widely used in the evaluation of classroom acoustic quality.In the international standard IEC 60268-16 and the national standard GB/T 12060.16-2017 revised according to the IEC standard,it is recommended that the minimum classroom target STI value is 0.62.Therefore,the purpose of this study is to obtain the relationship among RT,background noise level(BNL)and STI,and accurately derive the required RT and BNL according to the expected STI value,so as to establish the corresponding relationship among RT,BNL and subjective perception of speech intelligability,which is of great significance for the design and evaluation of classroom acoustic environment.In this study,we first selected representative 8 ladder classrooms and 3 small-scale classrooms as sample classrooms.Using standardized measurement methods and measurement procedures,the acoustic parameters such as RT,BNL and STI were measured,which obtained some classroom acoustic conditions with a large dynamic range,and provided accurate measured data for classroom acoustic simulation.Then,the acoustic software ODEON was used to establish the acoustic simulation model of each classroom,and the classroom simulation model was meticulously equivalent from the spatial modeling,sources and receivers setting,materials setting,parameters setting and other links.And refer to the measured data to continuously adjust the sound absorption to keep the simulated sound field consistent with the the actual sound field in acoustic characteristics.On the basis of these classroom equivalent models,the sound absorption coefficient of the materials in simulation models is changed proportionally,so that each classroom can obtain a wide range of reverberation conditions with a RT interval of 0.1s(the RT range of ladder classrooms is 0.4～2.6s,the RT range of smallscale classrooms is 0.4～1.8s),and 8 background noise conditions in the range of 25～60d BA are set with a gradient of 5d B.The two types of classrooms have obtained 1560 acoustic conditions.Finally,based on the statistical analysis of the large-scale acoustic parameter data obtained by the simulation,the relationship between the RT and STI under different background noise conditions,the relationship between the BNL and STI under different reverberation conditions,and correspondence among RT,BNL and STI are established in the ladder classrooms and small-scale classrooms.This study clarified the relationship among RT,BNL and STI,and matched the RT and BNL with speech intelligibility,which can provide theoretical and data support for the application of STI in the field of classroom acoustics,and provide reference and basis for classroom acoustic control and evaluation.