Since opening in 1930, Brisbane City Hall has been an important part of the city’s cultural and social events. Its Main Auditorium seats 1,600 and boasts a 120-year old Father Henry Willis organ as its centrepiece, and is a popular performance and event space. Having been comprehensively restored between 2009 and 2013 at a cost of $215m, 2014 saw a tender issued for a sound system for the circular, reverberant auditorium.

Distributor Hills and systems integrator Con-Sol worked with L-Acoustics on a design that would address the hall acoustics and accommodate restritive main rigging points. ‘The tender was very specific about the type of system that was required and imposed strict restrictions on the rigging of the main speaker arrays, with the need to design for a pre-determined single rigging point and a weight limit per array’, says Hills Systems Engineer, Damien Juhasz.

In addition to the rigging considerations, the circular venue posed an acoustic challenge: ‘The roof is a large dome, it has quite a long reverb time and there are a lot of reflections and focus points for the sound,’ says L-Acoustics Application Engineer, Germain Simon. ‘All the doors that lead into the auditorium focus energy towards areas in the centre, so the new system needed to focus sound on the audience areas as much as possible.’

The solution is based on an LR system of two flown full-range, variable curvature line source arrays, comprising ten Kara elements and two SB18 subwoofers each. Additional low-frequency reinforcement is provided by a central block of four SB18 subwoofers groundstacked under the front of the stage.

This is supplemented by a stage lip front fill system of six 8XT coaxial enclosures, an under-balcony fill system of 12 5XT coaxial enclosures and an in fill system of two 8XTi coaxial enclosures, mounted on the extreme left and right walls at the side of the stage. The two 8XTi fills are colour matched to the wall to lessen their visibility. Six 8XT coaxial enclosures serve as a distributed monitor system around the stage lip. The loudspeaker systems are powered by LA4X amplified controllers, which provide the signal routing and DSP for the system.

‘This Kara system was the perfect offering for this project,’ says Juhasz. ‘It’s lightweight, meeting the stringent rigging constraints, plus it has the wide horizontal dispersion and throw to cover the large audience area of the venue.’

After the initial inspection, the existing speaker cabling infrastructure was revealed to be inadequate for the new installation: ‘The building’s heritage status meant that we had to follow certain cable paths, the result being that some speaker cables were really long,’ says Juhasz. ‘We worked with the applications team at L-Acoustics who recommended ways to minimise the impact of these long runs on the performance of the system’.

The new system was also required to integrate with the venue’s existing voice alarm system, muting in the event of a fire alarm. This is achieved with a Crestron system that monitors the VA alarm state, controlling the LA4Xs via a dedicated control network.

The auditorium’s schedule of events meant that the installation window was extremely tight: ‘We focused a lot of effort on the sound levels, achieving a great result by flying the main system a bit higher then originally planned,’ Simon recalls. ‘We ended up with a very close match in both SPL levels and sound across the ground floor and balcony areas, and a vast improvement in speech intelligibility and even coverage across the audience areas.’