Evaluation of Speech Privacy in Passenger Cars of High-Speed Trains Based on Room Acoustic Parameters

Abstract

Speech privacy is important for improving the quality of the acoustic environment in high-speed train compartments because the conversation of other passengers is a major source of disturbing noises in high-speed trains. In order to provide an acoustic environment amenable to speech privacy, it is necessary to explore the room acoustic conditions of passenger cars in high-speed trains. The present study investigates speech privacy in the passenger cars of a high-speed train using the room acoustic parameters suggested in ISO 3382-3. Single-number quantities (D-2,D-S, L-p,L-A,L-S,L-4m, r(D) and r(P)) were measured in an example passenger car to evaluate the spatial decay of the sound pressure level and sound transmission index (STI). Computer simulations were also conducted to explore the effects of changing absorption coefficients and background noise levels on the single-number quantities. We found that D-2,D-S and L-p,L-A,L-S,L-4m values changed significantly with variation in average absorption coefficients, but that these parameters did not depend on the background noise levels. It was also found the privacy distance (r(P)), rather than the distraction distance (r(D)), to be a useful parameter for designing speech privacy in a passenger car, due to high background noise levels. The effect of absorption coefficients on r(P) was less than that of the background noise levels. In addition, regression models to predict the single-number quantities based on average absorption coefficients and background noise levels are suggested, and these can be used in practice to help with the design of acoustic environments promoting speech privacy in the passenger cars of a high-speed train.