Several functions affect speech intelligibility in a room. Among the more significant functions are the signal–to-noise-ratio (SNR), early decay time (EDT) and direct-to-reverberant ratio (D/R). These three acoustics objective measures are the primary influences on speech intelligibility, which are the main issues presented in this chapter. However, the amount of reflections in the room from an impulse sound signal may supersede the effects of SNR toward speech intelligibility. In addition, the acoustics characteristics of the room also influence the resulting sound level and thus the speech intelligibility. An in depth analysis on SNR, EDT and D/R has opened-up possibility of predicting speech intelligibility index by means of room’s physical quantities, and thus enabling sound system engineers and architects to have good indicators of how room will perform in terms of speech intelligibility, as early as the initial room design process
