Optimal classroom acoustic design with sound absorption and diffusion for the enhancement of speech intelligibility

Classroom design should be focused on the enhancement of the acoustic comfort for students and teachers. Long reverberation times and excessive noise levels can raise vocal effort and negatively affect speech intelligibility. Recent studies and standards updates have investigated whether acoustic treatment should include both absorbent and diffusive surfaces to account for the teaching and learning premises at the same time; however, studies under realistic conditions for the improvement of existing classrooms acoustics are still needed. In this work, an existing Italian classroom with poor acoustics was considered. Several solutions for treatment were simulated using CATT-Acoustics®, including adjustment of the absorption and scattering coefficients of surfaces differently configured to reach optimal reverberation time, and to increase Speech Transmission Index and Definition, especially for the positions in the furthest raw. The effectiveness of the acoustic treatment was also evaluated in terms of enhancement of speech intelligibility using the Binaural Speech Intelligibility Model (Rennies et al., 2013). Its outcomes are given as speech reception thresholds to yield a fixed level of speech intelligibility. Model predictions indicted an improvement in speech reception thresholds up to 6.8 dB after the acoustic intervention.