Design and Optimisation Of Voice Alarm Systems for Underground Stations

Voice Alarm systems (VA) are an essential part of subsurface underground station
emergency and evacuation systems. Their main purpose is to assist in the
management of emergency situations and evacuation procedures by providing key
verbal instructions to the occupants. However these life-critical systems will be
ineffective if the messages broadcast are unintelligible. Unfortunately, in most
London underground subsurface areas the announcements broadcast by the VA
system are not adequately intelligible and often do not reach a minimum specified
performance target.
The performance of VA relating to its electro-acoustic characteristics is relatively
complex and depends on multiple interrelated factors and operational constraints .
Underground stations present complex geometrical and architectural features which
severely challenge the achievement of satisfactory performance.
Despite the importance of VA system, there are few works in the literature providing
practical and applicable design knowledge in the context of real world underground
spaces. Moreover contractual performance requirements are not suitably laid out
and this can lead to ineffective designs.
This research aims to provide practical design knowledge and understanding for the
improvement of VA speech intelligibility performance in underground spaces.
Research results were derived from measurements and designs undertaken for real
scenarios. A specific knowledge base is provided on the acoustics of underground
spaces, speech intelligibility and VA systems. A critical review of relevant research
and performance specifications and standards is undertaken and a new
performance design parameter is proposed. An empirical prediction model tool
based on a large pool of measured survey data is developed for the prediction of the
Speech Transmission Index of VA on platforms. A validating and comparative study
is undertaken for two widely used commercial acoustic simulation programs to
assess their suitability as design tools for VA systems on platforms, CATT-Acoustic
and Odeon. The impact on VA performance of design variables are investigated
using a computer simulation of a representative platform. A novel acoustic treatment
design concept is proposed. The Yang quasi diffuse sound field theory for platforms
is verified and derived knowledge expanded. Practical design recommendations are
provided as well as suggestion for further work.