Relationship between speech transmission index and easiness of speech perception in reverberatory fields

Abstract

When evaluating speech intelligibility in rooms, the Tri-syllable articulation test is used as one of the standard indicators in Japan. Sometimes there are differences between auditory impression and the score of the articulation test. So the psychological scale values of easiness of speech perception (ESP) were measured by experiments, which indicated differences between ESP and articulation scores and a good correlation (R=0.9) between ESP and speech transmission index (STI) in reverberation. The purpose of this paper is to point out relationships between the condition of sound field and ESP. The first of two experiments in this study was done in reverberatory fields. Sound-pressure level (SPL) of direct sound, direct sound to first reflection ratio (D/R), initial delay time, frequency characteristics of reverberation, and reverberation time (RT) were varied. The other experiment was done in simulated fields of actual auditoriums. The result of the first experiment shows D/R and RT has alarge effect on ESP and while varying D/R, the correlation between ESP and STI is not good (R=0.6). The second experiment indicates that when the sound source is on the center of the stage, the correlation between STI and ESP is 0.8; and a different tendency is found while using the sound reinforcement system.