Experimental comparison of speech transmission index measurement in natural sound rooms and auditoria

Abstract

Speech intelligibility is an important factor for natural sound quality evaluation in rooms and auditoria. As an objective metric for predicting speech intelligibility, the application of the speech transmission index (STI) has increased significantly in recent years. In this study, three measurement systems were selected to measure the STI and speech transmission index for public address systems (STIPA) of 44 listening conditions at 11 receiver positions in 4 rooms. Thereafter, to explore the substantial differences among the three systems, three new measurement systems were developed, and the STI and STIPA under the same 44 listening conditions were measured again. The results reveal the following: (1) An obvious difference existed among the measurement results of the three selected systems, mainly caused by the influence of the sound source directivity, as well as the possible influences of the test signal sound pressure level calibration and the calculation procedure. The directivity of the microphone as well as the presence of a human body near the microphone influence the STI measurement results, although these affects are relatively small. (2) A small difference existed between the STIPA and STI, mainly owing to the room frequency response characteristics. (3) There was no essential difference between the measurement results of the indirect and direct methods; STI can be considered to expand the application scope of the indirect method. The findings in this study are significant for the application of the STI in the field of architectural acoustics.