Classroom acoustics design for speakers’ comfort and speech intelligibility: a European perspective

Current European regulatory requirements or guidelines for reverberation time in classrooms have the goal of enhancing speech intelligibility for students and reducing noise levels in classrooms. At the same time, school teachers suffer frequently from voice problems due to high vocal load experienced at work. With the aim of improving teachers’ working conditions, this paper proposes adjustments to current regulatory requirements on classroom acoustics in Europe from novel insights on classroom acoustics design that meet simultaneously criteria of vocal comfort for teachers and speech intelligibility for students. Two room acoustic parameters are shown relevant for a speaker: the voice support, linked to vocal effort, and the decay time derived from an oral-binaural impulse response, linked to vocal comfort. Theoretical prediction models for room-averaged values of these parameters are combined with a model of speech intelligibility based on the useful-to-detrimental ratio and empirical models of signal-to-noise ratio in classrooms in order to derive classroom acoustic guidelines, taking into account physical volume restrictions linked to the number of students present in a classroom. The recommended values of reverberation time in fully occupied classrooms for flexible teaching methods are between 0.45 s and 0.6 s (between 0.6 and 0.7 s in an unoccupied but furnished condition) for classrooms with less than 40 students and volumes below 210 m3. When designing larger classrooms, a dedicated acoustic study taking into account considerations about geometry, material and speaker/audience placements can help to provide good speech intelligibility across the audience, while increasing the voice support and reducing the vocal effort.