Impact of Echo Interference on Speech Intelligibility in Extra-Large Spaces

In extra-large spaces, the varying distances between distributed loudspeakers and listeners lead to sound delays in the loudspeakers’ concentrated projection areas. When combined with the inherent long-delay reflected sounds in those spaces, this dual effect exacerbates the echo problems and poses challenges to maintaining speech intelligibility. To explore the influence mechanism of echo interference on speech intelligibility in extra-large spaces, a questionnaire survey was carried out in two representative extra-large buildings, and then listening experiments were conducted in the laboratory under different echo conditions and impulse characteristics. The results highlighted that (1) apparent echo problems existed in extra-large spaces and severely affected speech intelligibility; (2) the echo phenomenon can be classified into three groups—no echo (0 ms), short delay (100 or 200 ms), and long delay (≥300 ms)—with the detrimental effect on intelligibility increasing across the groups; and (3) a curve was established to describe the relationship between speech intelligibility and STI in extra-large spaces, and compared with the standard curve, the STI thresholds require further adjustment. These findings indicate that echoes in extra-large spaces significantly impair speech intelligibility and reduce the accuracy of its prediction, and therefore should not be neglected.