The largest in Australia, Sydney’s Central Railway Station has installed a Martin Audio OmniLine loudspeaker system to address long-standing speech intelligibility problem.
The Country Trains Concourse – measuring 110m x 60m x 10m, and with a challenging RT60 time of 5.5s in the mid-band – has defied previous attempts to deliver intelligible announcements to commuters. Many solutions have tried and failed to tame the high level ofreverberation caused by a combination of terrazzo floors, sandstone and plate glass walls and a high arched steel roof. Last year Glenn Leembruggen, principal of Acoustic Directions, became the latest specialist to do battle with the acoustically hostile environment.
Since acoustic treatment of the inside of the roof was declared financially untenable, the Acoustic Directions team’s David Connor and David Gilfillan tested several software-driven systems, and investigate different steerable line array solutions. They concluded that a Martin Audio OmniLine system, with DSP processing, would produce the best quality and best speech clarity, and specified 120 steered elements. These were supplied by TAG, Martin Audio’s Australian distributor.
The installation used a special version of the Martin Audio Display software (operating under an FIR filtering regime that addressed every element in the array with its own processed channel). The intelligent software enabled the array to be configured to deliver sound precisely over the venue’svertical profile without spillage. Further, elimination of high-frequency side-lobes gives OmniLine an advantage over conventional DSP steered columns making it suitable for high quality speech and music reproduction even in reverberant spaces such as railway station concourses.
With this system, Acoustic Directions was able to simultaneously optimise the direct field over the listening area, keep the sound off reflective rear walls, and minimise reverberant sound power. The result is remarkably high intelligibility throughout the concourse, even at rush hour, when as many as 3,000 passengers are adding to the cacophony of noise resonating around this vast cavern.
With the amps situated as much as 200m away from the speakers, a 100V system was required, and Acoustic Directions worked with Harbuch Electronics to develop a loudspeaker transformer with only 10° of phase shift at 20kHz. The FIR filters that beam control the array are implemented in Nion processors with the loudspeakers being driven by eight-channel 2.4kW amplifiers (to provide 120 amplifier channels).
Acoustic Directions optimised the frequency responses over the listening area using time-windowed impulse responses.
The installation also picked up a coveted Rutledge AV Industry Award (an AVIA) with the judges commending Acoustic Directions’ meticulous implementation of the modelling, installation and commissioning of the system.
As a result, not only can amplified speech be easily understood in any part of the concourse for the first time, but music and pre-recorded messages sound natural and clear – and roaming hand-held wireless microphones can function without fear of feedback. Such is the confidence inspired by the solution, that special events, promotions and even live music events are being hosted at the Central Railway Station using the house sound system.
More: www.tag.com.au
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