Effects of acoustical descriptors on speech intelligibility in Hong Kong classrooms

This study investigated the effects of classroom acoustics on speech intelligibility in secondary school and university classrooms. Speech intelligibility tests were conducted in 9 secondary school classrooms and 18 university classrooms and the acoustical measurements were performed in these classrooms. Subjective speech intelligibility tests were obtained from phonetically balanced (PB) word lists on a total of 672 students and acoustic descriptors such as signal-to-noise ratio (SNR), early decay time (EDT), and sound clarity (C₈₀) were conducted in different listening positions in each classroom. The relationships between speech intelligibility scores (SI) and acoustical descriptors were fitted based on non-linear curve fitting regression models. The “S” form regression model was selected with modification as the basic regression equation to describe the effects of SNR on speech intelligibility. The combination effects of SNR with reverberation condition and sound clarity condition on speech intelligibility were investigated. The impact of different age groups and linguistic environment on speech intelligibility were discussed. The results reveal that SI increases with the increase of SNR value for all age groups. The results indicate that nearly 0.06 s increasing in EDT values will result in a 1% decrease in SI. Furthermore, the results also suggest that a 1 dB increasing in C₈₀ values will result in a 1.23% increase in speech intelligibility scores. The SI increases as the age increases under the same SNR condition. The speech intelligibility scores are always lower than the comparison research results with a constant reverberation value as well as sound clarity value for an equal SNR value.