Assessment of speech intelligibility in university lecture rooms

Abstract

Speaking and listening are the primary modes of communication at educational institutions. The learning process requires intensive verbal communication between students and teachers; as well as among students. Students spend from 45% to 75% of their time in the lecture room listening to their teachers and classmates. So, intelligibility of spoken words is obviously very important for successful learning environment. Learning process becomes slower in educational environments that have consequently impaired speech intelligibility. Researches carried out globally show that acoustical performance is one of the major problems in educational institutions especially in universities. These indicate to a number of problems associated with acoustical performance, while unsatisfactory speech intelligibility is one of them. In Bangladesh, higher education scenario has been transformed rapidly with growing number of new academic buildings. Based on published documents, no study has been carried out till now to determine the acoustical performance of these universities. This research aimed to evaluate the existing speech intelligibility condition in university lecture rooms conducting lectures in Bangla. Previous researches have established that compared to English, Bangla requires more stringent conditions for speech intelligibility. The research follows quantitative approaches; comprising of experiment, computational and analytic methods. For the convenience of conducting the research in terms of accessibility and scale, universities of Gazipur district have been selected for the study. Quantitative data are collected from three universities, namely Dhaka University of Engineering and Technology (DUET), Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU) and Bangabandhu Sheikh Mujibur Rahman Digital University (BSMRDU). 10 types of lecture rooms of DUET, BSMRAU and BSMRDU are selected after sampling procedure to collect quantitative data. Data collection is carried out under 4 different listening conditions. These are condition 1: fan on, window and door open; condition 2: fan on, window and door closed; condition 3: fan off, window and door open; and condition 4: fan off, window and door closed. The results show that Percentage Syllable Articulation (PSA) values, that is determining factor to evaluate speech intelligibility, remain below 75% under all listening conditions. This implies that all the listening conditions have an unsatisfactory level of speech intelligibility. Results also show that long Reverberation Time, high Background Noise Level, low Sound Pressure Level and low Signal to Noise Ratio have combined effect on speech intelligibility. Due to the combined effect of those factors, average PSA values are 26.82%, 23.93%, 36.02%, and 32.24%, for condition 1, 2, 3 and 4, respectively. The findings of this study will help as design and redesign guidelines for acoustics for educational buildings in Bangladesh or other places, where Bangla-language communication takes place. The results will also raise awareness among relevant design and client groups about the acoustical concerns of educational buildings and motivate future design initiatives. Keywords: Acoustical performance, speech intelligibility, university lecture room, Bangla language.