Brisbane City Hall installs L-Acoustics sound system

Brisbane’s City Hall has installed an L-Acoustics sound system in its 1,600-capacity Main Auditorium.

In June 2014, a tender was issued for a set-up that could improve sound in the circular, reverberant space. Australian L-Acoustics distributor Hills and systems integrator Con-Sol worked with the manufacturer to propose a system 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," said 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,” explained 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 subs 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,” remarked 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,” said 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.

Simon concluded: “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 exceeded their expectations. The even SPL coverage, speech intelligibility and gain before feedback has resulted in improved flexibility in microphone positioning and, in turn, a more versatile application portfolio for the event planners.