A Wizard Of Oz: L-Acoustics Tames Brisbane City Hall
Upon its opening in 1930, Brisbane City Hall immediately became, and has remained, the backdrop to many of the city’s cultural and social activities. Its iconic circular Main Auditorium, which seats 1,600 and boasts a famous 120-year old Father Henry Willis organ as the centrepiece, is one of the city’s best-loved performance and meeting spaces. The building was comprehensively restored between 2009 and 2013 at a cost of $215 million.
In June 2014, seeking a system that could improve sound in the circular, reverberant space, a tender was issued. Australian L-Acoustics distributor Hills and systems integrator Con-Sol worked with L-Acoustics to propose a solution that would not only address the challenging acoustics, but also fit within the restriction guidelines of the main rigging points. The L-Acoustics solution was selected after a comprehensive evaluation process that included a full system demonstration with independent system measurements and listening tests.
“The tender was very specific about the type of system that was required and also imposed very strict restrictions on the rigging of the main speaker arrays, with the need to design for a pre-determined single rigging point and a 450kg weight limit per array,” says Damien Juhasz, Systems Engineer at Hills.
In addition to the rigging restriction, 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. 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,” says Germain Simon, L-Acoustics Application Engineer.
The L-Acoustics solution is based on a Left Right system of two flown full range, variable curvature line source arrays, consisting of ten Kara elements and two SB18 subwoofers each. Additional low frequency reinforcement is provided by a central block of four SB18 subwoofers ground stacked under the front of the stage.
The main system is supplemented by a stage lip front fill system of six 8XT coaxial enclosures, an under balcony fill system of 12 5XT compact 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 in fill loudspeakers were colour matched to the wall to minimise visual impact within the heritage venue. A system of six 8XT coaxial enclosures was supplied as a distributed monitor system around the stage lip. The system is entirely 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 Damien 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 it was determined that the existing speaker cabling infrastructure would not meet the requirements of the proposed system. “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 Damien 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 system was required to integrate with the venue’s existing Voice Alarm system, muting in the event of a fire alarm. This was achieved by utilising a third party control system from Crestron to monitor the VA alarm state, controlling LA4X amplified controllers via a dedicated control network.
The auditorium’s busy schedule of events only allowed for installation and commissioning to be carried out overnight, with two nights taken for the
Germain Simon concludes, “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. 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 evenness of coverage across the audience areas.”
The end result for the venue was a number of key improvements that far exceeded their expectations. The even SPL coverage, speech intelligibility and gain before feedback has resulted in significantly improved flexibility in microphone positioning and, in turn, a more versatile application portfolio for the event planners.