Quantifying public address system performance in a public transit environment
Keywords:Acoustics, Computer software, Loudspeakers, Reverberation, Speech intelligibility, Speech transmission, Speech transmission index (STI)
AbstractThe Toronto Transit Commission (TTC) new Sheppard subway line is nearly complete. It adds 5 new stations and 6.4 km of tunnel to their system. From the beginning of the overall design of the stations, efforts were made to ensure the public would be able to understand public address(PA)announcements during revenue service and in emergency situations. The PA system design goal was a speech transmission index (STI) of 0.45 or 'Fair' intelligibility. As each station is completed, it is being measured using Maximum Length Sequences in a PC based measurement system in order to validate the performance of the PA and the station architectural treatment. The paper will discuss the PA system used, summarize the measurements, provide some assessment as to the performance of acoustic treatments used in the station finishes as well as comment upon the practical aspects of using the Dirac measurement system.
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