The largest train station in Australia, Sydney’s Central Railway Station, has been installed with a Martin Audio OmniLine System to remedy years of persistent speech intelligibility issues.
Measuring 110m x 60m x 10m and cited as having a RT60 time of 5.5 seconds in the mid band, the main Country Trains Concourse had defied previous attempts to solve the intelligibility issues due to inherent reverberation caused by a combination of terrazzo floors, sandstone and plate glass walls and a high arched steel roof.
Audio specialist Acoustic Directions was charged with specifying a system that didn’t require acoustical treatment to the inside roof section.
The Martin Audio OmniLine system, with DSP processing, was opted for as it produced the best quality and best speech clarity during testing. 120 steered elements were subsequently specified — supplied by Martin Audio’s Australian distributors, TAG.
Several versions of Martin Audio Display software were used for the installation (operating under an FIR filtering regime that addressed every element in the array with its own processed channel), to enable the array to be correctly configured so it could deliver sound precisely over the venue’s vertical profile without spillage. This also helped keep sound off the reflective rear walls, and minimise reverberant sound power.
With the amps situated as much as 200m away from the speakers, a 100 Volt system was required. Acoustic Directions worked with audio consultants Harbuch Electronics to develop a 100V loudspeaker transformer that was ultra-flat and with only 10º of phase shift at 20kHz. The FIR filters that beam control the array are implemented in Nion processors with the loudspeakers being driven by 8-channel 2.4kW amplifiers (to provide 120 amp channels).
In addition, Acoustic Directions optimised the frequency responses over the listening area using time-windowed impulse responses.
The resulting system can, for the first time, not only permit intelligibility, but also play music and pre-recorded messages with natural and clear sound — and roaming hand-held wireless microphones can function without the possibility of feedback.