The importance of early reflections for speech intelligibility in rooms

Abstract

New results demonstrate that in rooms for unamplified speech communication early reflections are important for achieving adequate speech intelligibility and that early reflection energy is typically much greater in magnitude than the direct sound energy. Speech intelligibility was measured using a rhyme test in simulated sound fields that included a direct sound with varied early reflections and reverberant sound along with a constant level of ambient noise. The results confirmed that added early reflection energy is equivalent to increased direct sound energy. The combination of direct sound and early reflections increases the effective signal-to-noise ratio and the related speech intelligibility scores for both impaired and nonimpaired listeners. The new results also show, that for common conditions where the direct sound is reduced, it is only possible to understand speech because of the presence of early reflections. Analyses of measured impulse responses in rooms for speech, in terms of a measure of the benefit from early reflections, show that early reflections can increase the effective signal-to-noise ratio by up to 9 dB. The primary goal of room acoustics design should be to maximize early reflection energy to make possible increased effective signal-to-noise ratios.