Speech and noise levels measured in occupied K-12 classrooms.

This project acquired sound levels logged across six school days and impulse responses in 220 classrooms across four K-12 grades. Seventy-four percent met reverberation time recommendations. Sound levels were processed to estimate occupied signal-to-noise ratios (SNRs), using Gaussian mixture modeling and from daily equivalent and statistical levels. A third method, k-means clustering, estimated SNR more precisely, separating data on nine dimensions into one group with high levels across speech frequencies and one without. The SNRs calculated as the daily difference between the average levels for the speech and non-speech clusters are found to be lower than 15 dB in 27.3% of the classrooms and differ from using the other two methods. The k-means data additionally indicate that speech occurred 30.5%-81.2% of the day, with statistically larger percentages found in grade 3 compared to higher grades. Speech levels exceeded 65 dBA 35% of the day, and non-speech levels exceeded 50 dBA 32% of the day, on average, with grades 3 and 8 experiencing speech levels exceeding 65 dBA statistically more often than the other two grades. Finally, classroom speech and non-speech levels were significantly correlated, with a 0.29 dBA increase in speech levels for every 1 dBA in non-speech levels.