Australian Acousticians ensure Railway Platform Announcements are Easier on the Ear
An innovative loudspeaker system designed to render railway platform announcements easier on the ear is being rolled out across many of the approximately 250 New South Wales stations in Australia.
The sound system is the culmination of five years work by Sydney acousticians David Gilfillan and Glenn Leembruggen for Railcorp, the NSW Government department responsible for operating the Sydney Metropolitan rail network.
Glenn is principal of Acoustic Directions and ICE Design, and an Associate of the University of Sydney, while David is principal of Gilfillan Soundwork and ICE Design. Glenn is also a member of UK professional body the Institute of Acoustics, which has more than 3000 members worldwide working in acoustics, noise and vibration. The Australians have presented research on the system to fellow acousticians in the UK.
RailCorp asked Glenn and David to design a system that would improve the quality of announcements at Central Station Sydney, and then to design a similar prototype system for roll-out to the suburban network.
It had to provide natural sounding speech and maximise intelligibility of announcements, while providing a ‘calming and authoritative’ influence in case of an emergency.
The system also had to minimise spillage of sound to adjacent platforms and neighbouring properties.
“Passengers on station platforms can often be considered as ‘vulnerable listeners’ as so many acoustic factors in this environment are hostile to the achievement of satisfactory speech intelligibility,” said Glenn.
“To address this vulnerability, the system needed to provide intelligibility that is robust under the diverse range of acoustic conditions that waiting passengers experience.”
This presented a challenge, given the “difficult acoustic environment of multiple railway platforms” and high background noise, the acoustic experts said.
The announcement systems Glenn and David developed were a “significant improvement in performance from previous sound systems on railway platforms in New South Wales and probably most of the world”.
For Central Station, they developed customised loudspeakers using acoustic techniques, to steer sound toward where it was needed and away from unwanted areas such as residents or adjacent platforms.
The loudspeakers are incorporated into a time-sequenced system; each loudspeaker being time synchronised to the one behind it. The speakers are powered by small locally situated amplifiers.
“Each amplifier module contains digital signal processing that allows delay to be added to the signal of individual loudspeakers,” said the acousticians.
“Loudspeakers are arranged so that the main body of sound is projected along rather than across the platform. This allows RailCorp to simultaneously make different announcements to adjoining platforms, whilst maintaining intelligibility on both platforms.”
Announcement sound levels too were examined and adjusted to lie within a comfortable range for travellers and to take account of, at times, high levels of background noise.
“It was found that a 0.6dB increase in announcement level for every 1dB increase in background noise level satisfied the requirements of listener comfort and intelligibility. The softest level of announcement was appropriate for the quietest times of the day, while the loudest level was not too loud for comfort,” said David and Glenn.
They commended RailCorp for its commitment to the process of acoustic design and implementation that will ultimately yield significant improvements to speech intelligibility for its customers at NSW stations.
