Journal of Korean Institute of Architectural Sustainable Environment and Building Systems ISSN:1976-6483(Print) 2586-0666(Online) 한국건축친환경설비학회논문집

The useful-to-detrimental sound ratios (U₅₀) measure can be more practically useful means of assessing and understanding real classroom situations because it can be easily obtained from both measured clarity (C₅₀) and signal-to-noise-ratio (SNR) values in classrooms during speech communication. The goal of this work is to better understand room acoustics conditions for real speech communication during actual lectures and to provide U₅₀ values for achieving ‘good’ acoustical conditions for speech intelligibility in university classrooms. In the present work, U₅₀ is determined from both measured C₅₀ and SNR values during 15 actual lectures in 11 university classrooms in Korea. The linear regression results for speech transmission index (STI) and U₅₀ values show that classrooms having U₅₀ values greater than +4.1 dB correspond to STI values of 0.60, indicating ‘Good’ acoustical conditions for speech intelligibility. The U₅₀ value is 0.9 dB lower than that of the previous study made in quietly occupied classrooms without student activities. The present result indicates that the noise level is not the same as experienced during actual lecturing situations in university classrooms. When the classroom has a SNR (125-4k) value of 7.7 dB or lower a C₅₀ (125-4k) value of 7.3 dB or greater to be required for achieving good acoustical conditions during lectures in university classrooms.