Research On The Influence Of The Distribution Characteristics Of The Early Reflection Sound In The Classroom On The Intelligibility Of Speech

In the process of teaching,the classroom is required to have high language clarity to ensure the effect of language communication between teachers and students.Reverberation time,signal-to-noise ratio,sound pressure level,frequency transmission characteristics,sound energy ratio and other factors have an impact on speech intelligibility.There have been many research results in these areas.In addition,the early reflected sound helps to enhance the direct sound and improve the speech intelligibility.The early reflected sound is generally regarded as the reflected sound in the 50ms after the direct sound,but the influence of its time,space and energy distribution on language clarity is not clear enough,which is worthy of further study.In this paper,the effects of time distribution,spatial distribution and energy distribution of early reflected sound on speech intelligibility were studied,and the research results was applied to the acoustic transformation of the classroom.The specific work was as follows:（1）A study on the influence of the energy distribution of early reflected sound on speech intelligibility.Through the signal processing of the indoor impulse response measured in the actual classroom,under the condition that the ratio of the early reflected sound energy to the total sound energy is constant,the early sound energy was concentrated in several different delay periods:0ms～10ms,0ms～20ms,0ms～30ms,0ms～40ms,0ms～50ms,10ms～20ms,20ms～30ms,30ms～40ms,40ms～50ms.Without changing D₅₀,the more concentrated the early sound energy was,and the higher the time interval of sound energy concentration was,the better the language clarity was.To obtain the best language clarity,the early reflected sound energy should be concentrated in the 30ms.（2）A study on the influence of the time distribution of early reflected sound on speech intelligibility.The subjective speech intelligibility listening experiment was carried out through headphone playback,and the influence of the time distribution of early single reflected sound on Chinese speech intelligibility was obtained under the condition of different background noise and different signal-to-noise ratio.In various cases,the early reflected sound in the delayed 20ms had a significant gain on language clarity,while the early reflected sound after 30ms weakens or even impairs the speech clarity.（3）A study on the influence of the spatial distribution of early reflected sound on speech intelligibility.The effects of early reflected sound from the front and rear of the horizontal plane,20°elevation above the horizontal plane and 40°elevation above the horizontal plane on the articulation of Chinese language were studied.It was found that there was no difference in the gain effect of the early reflected sound from the front and the rear on the language clarity from the same plane,but the gain range of the early reflected sound on the language clarity was different on different elevation planes.Combined with the actual situation in a specific classroom,the trend of Chinese speech intelligibility was studied when several early reflected sounds from side walls and ceilings are added.It provided a basis for the practical application of early reflected sound.（4）Combined with the above research results,aiming at the weak position of language clarity in the classroom,a layout scheme of sound absorption material and reflection material was designed to transform the classroom to improve the early and late sound energy ratio C₅₀.In addition,it can also improve indoor language clarity and improve the acoustic environment of the classroom.