Evaluation of acoustical conditions for speech communication in active university classrooms

Abstract

One can measure speech and noise levels separately but then the noise is not the same as experienced during the speech communication in active classrooms. In this study, the acoustical conditions in university classrooms during actual lecturing situations were measured and evaluated based on real recordings of combined speech and noise sounds. Acoustical measurements and recordings were made during actual 15 lectures in 11 university classrooms in Korea. A statistical method was used for obtaining octave band speech and noise levels in university classrooms during actual lectures from the recordings of combined speech and noise sounds. In the 11 active Korean university classrooms the adult students experienced on average: speech levels of 51.5 dBA (s.d. = 2.7 dBA), noise levels of 44.3 dBA (s.d. = 2.1 dBA), and a speech-to-noise ratio of 7.2 dBA (s.d. = 2.7 dBA). The mean speech source level of the 15 Korean instructors was 11 to 12 dBA lower than the two previous studies made in the 11 University of British Colombia classrooms (64.5 dBA, s.d. = 4.2 dBA) and 27 elementary school classrooms (65.3 dBA, s.d. = 2.5 dBA) in Canada. Both measures, the useful-to-detrimental ratio, U50(125–4 k), and the speech transmission index, STI, for speech intelligibility are highly correlated and essentially assess almost the same characteristics of university classrooms. The present results show that university classrooms having U50(125–4 k) values greater than +4.1 dB, will have STI values of 0.60 or higher, which indicates ‘Good’ acoustical conditions for speech intelligibility.