Acoustical design for public address announcements in an underground subway station

The public address (PA) is a part of the passenger information system in an underground subway station. A sample station named Xingzhong Road on metro line 9 in Shanghai is considered in this paper. A ray-tracing model for acoustical simulation of the PA system is established. Verification is performed by comparing the simulated and the measured sound pressure levels (SPLs), early decay time (EDT), reverberation times (RTs) and clarity (C50). Several sound samples are simulated by changing the ceiling absorption materials of the subway station model. Jury tests of these sounds are conducted by using the paired-comparison method (PCM). We found that people prefer a shorter RT, which demands higher sound absorption materials. The relationship between the RTs and the averaged absorption ratios of the ceiling materials suggests that the RT around 1 s is the best in the Xingzhong Road station, and the values of the objective parameters, such as the SPL, EDT, speech transmission index (STI) and echo speech, are acceptable to PA system. The method presented in this paper can be regarded as a useful tool for acoustical optimization design of the subway station PA system.