Martin Audio OmniLine loudspeaker arrays has been specified and installed at Central Railway Station in Sydney, the largest in Australia, to address speech intelligibility problems that have persisted for years.
The Country Trains Concourse, measuring 360 x 196 x 32 feet with a challenging RT60 time of 5.5 seconds in the mid-band, has long defied attempts to get intelligible announcements heard by commuters.
Over the years, many brands have successively tried and failed to tame the inherent reverberation 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 ruled out as being financially untenable, two members of the Acoustic Directions team, David Connor and David Gilfillan, decided to trial several software-driven systems and different steerable line array solutions.
They ultimately concluded that a Martin Audio OmniLine system, with DSP processing, would produce the desired quality and speech clarity, and specified 120 steered array elements supplied by TAG, Martin Audio’s Australian distributors.
Modular and scalable, this particular OmniLine installation used a special version of the Martin Audio Display software (operating under an FIR filtering scheme 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’s vertical 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.
Acoustic Directions were thus able to simultaneously optimize the direct field over the listening area, keep the sound off reflective rear walls, and minimize reverberant sound power. The result is 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 amplifiers situated as much as 650 feet away from the speakers, a 100-volt system was required, and Acoustic Directions worked with Harbuch Electronics to develop a 100-volt loudspeaker transformer that was ultra-flat and with only 10 degrees of phase shift at 20 kHz. The FIR filters that beam control the array are implemented in Nion processors with the loudspeakers being driven by 8-channel 2.4 kW amplifiers (to provide 120 amp channels).
Acoustic Directions optimized 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, for the first time not only can amplified speech be easily understood in any part of the concourse, but music and pre-recorded messages sound natural and clear—and roaming hand-held wireless microphones can function without fear of feedback.
In fact, such is the confidence inspired by this new solution, that special events, promotions and even live music events are being hosted at Sydney’s Central Railway Station using the house system.