Jian Kang
The Martin Ctr., Cambridge Univ., 6 Chaucer Rd., Cambridge CB2 2EB, UK
Multiple loudspeaker public address systems are often used in long enclosures, such as underground stations, where one dimension is much greater than the other two. Classic room acoustic theories cannot be used in long enclosures as the assumption of a diffuse sound field is not satisfied. In this research a theory of reverberation in long enclosures is established [J. Kang, Acustica (to be published)]. It is shown that the reverberation in long enclosures varies systematically with the source--receiver distance. Based on the theory, a computer program for calculating the speech transmission index (STI) of multiple loudspeakers in long enclosures was developed, with which the optimal loudspeaker directionality and spacing can be determined. With the help of this program, a series of treatments for improving the speech intelligibility of multiple loudspeakers were investigated in a 1:16 scale model of St. John's Wood station in London. It was found that the STI can be improved effectively by diffuse treatments and strategic positioning of absorption. Some of the above results are being used for the new Hong Kong airport-underground project. [Work supervised by Dr. R. J. Orlowski and supported by MTRC, ORS, and COT.]