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10 Aug 2015

Brisbane City Hall : Taming Reflective Acoustics with L-Acoustics 

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Brisbane City Hall has stood imposingly over King George Square since 1930. In Italian Renaissance style, it’s grand and opulent, with an auditorium to match. However, its architects sadly never foresaw the electroacoustic issues that would be caused by basing the auditorium’s shape on The Pantheon in Rome. “It’s extremely difficult,” said Damian Juhasz, Audio Systems Engineer at Hills. “It’s circular, it’s reflective. It’s a beautiful room, but it’s an acoustic nightmare. I mean, it’s a circular room with a crescent balcony and a dome! There has been some acoustic treatment done – there are panels of absorbent material on the walls. But there’s an interesting effect; the doors are reflective so when they’re closed, they focus acoustic energy in radial lines back into the centre of the room!”

Distributed Solution

Unsurprisingly, the Hall had long been looking for a solution to their acoustical conundrum. A new proposal was put forward by consultancy DesignStage, which went out to public tender. “It was a prescriptive tender,” explained Damian. “It was a ‘design and construct’ proposition, but at the same time looking for a PA system that satisfied a strict set of requirements; left-right, front fill, under-stage subwoofers and a distributed under- gallery fill. The successful bidder would need to design a system that satisfied those criteria as well as providing optimal performance in the space.”

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Realising that responding to the tender would require a lot more than a gear list, a team came together to respond. Gold Coast production company and integrator con-sol, who had worked in the venue as an external provider, were already across the tender and had worked previously with DesignStage. “We did the site inspection with venue management.” Said con-sol’s Managing Director Bill Karaitiana. “We realised they weren’t after a sound system, they were looking for a solution to a fairly big problem. To say that auditorium is reverberant is an understatement; it’s incredibly reflective. That’s how it was approached from the start – it needed a solution.”

Damian

Damian Juhasz

The French Touch

Damian and Hills worked with con-sol on a response, which they both knew would be a perfect fit for legendary French manufacturer L-Acoustics. “We worked closely with the application engineers at L-Acoustics,” Damian elaborated. “L-Acoustics won’t simply supply a bunch of boxes to a venue; all of their systems are designed as systems. Their tender responses have to satisfy both the requirements and their own internal quality standards.” The response piqued the venue’s interest, and L-Acoustics were invited to a shootout against two other leading brands.

Normally, a shootout of three PAs in an auditorium would involve a single mono hang of each at centre stage. Not so for Brisbane City Hall, who insisted on having as many elements in place as possible. “We put in full left-right hangs, subwoofers under the stage and even the under-balconies,” recalled Damian. “The under-balconies were tricky because of the curved balcony section. There’s six either side on a crescent- shape balcony split into two runs and time aligned. For the demo we did half the balcony.” con-sol were on hand to get the gear in and set-up. “We provided Brisbane City Hall with everything the tender required with the exception of the stage monitors,” clarified Bill Karaitiana. “L-Acoustics application engineer Germain Simon flew out for the shootout, and attended in conjunction with Damian. We were all asked to leave the room during the shootout, and leave one representative behind. We nominated Germain.” After a thorough evaluation of all three contenders, L-Acoustics came out the winner.

Gear Up

The final system design is a left-right system of two flown full-range, variable curvature line arrays, with each side running 10 elements of KARA and two SB18 subwoofers. “There was a 450kg weight restriction on the main arrays,” Damian interjected. “But they also wanted flown subs if the weight allowed for it. We were lucky and just snuck in.” The flown subs are augmented by four SB18 subwoofers ground stacked under the front of the stage.

The front fill is made up of six 8XT loudspeakers, each sporting an 8” coaxial transducer and 1.5” compression driver, that can be struck when not needed. The under balcony fill system consists of 12 5XT compact coaxial enclosures, supplemented by an in-fill system of two 8XTi coaxial enclosures. On stage, six 8XT run as a monitor system. The whole installation is powered by 12 LA4X amplifier/controllers, which provide the signal routing and DSP for the system, in addition to four channels at 1000W per unit.

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Making Predictions

The performance and design of the PA was mapped out both in L-Acoustics’ own Soundvision modelling software as well as EASE. As KARA is physically steered, measurements had to be precise. “The DSP is used for line array optimisation,” Damian illustrated. “The angle of the array and inter-element angles within the array are what optimise coverage in the audience area. The auditorium has more than 2 1⁄2 seconds of reverb time, so we needed to focus the acoustic energy onto the audience as much as possible. The project required modelling in the initial phase, which L-Acoustics provided. Every system installed is vetted by both L-Acoustics and Hills.”

Working in a heritage building always has challenges. “Cabling issues were the biggest problem presented by the heritage overlay,” observed Bill. “We didn’t have the luxury of straight runs. Some of them are over 100 metres. The left-right cable run is routed through a ventilation shaft that was re-fireproofed afterwards.” The EWIS also had to interface with the PA. “There’s no local capability to do that on the amplifiers,” Damian noted, “so we installed a Crestron RMC3 controller that works in parallel with the L-Acoustics system. It monitors the contact closure from the EWIS for an alarm state. If activated, it will trigger a system-wide mute of the performance system.”

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The Voice of Authority

The Hall’s new PA capabilities mean the venue will now attract a wider variety of events and hirers. “The auditorium’s always been limited, but the scope’s wider now,” mused Bill. “They can do everything from speech to elaborate concerts.” Confirmation of the enormous improvement in performance came not long after the project’s completion. “We got a phone call after the first mayoral speech on the system,” Bill related. “Apparently, the mayor got up and said ‘Will everyone please take your seats?’, and they did. The regular venue tech told me he was shocked; ‘Normally we have to ask three or four times’ he said. The mayor came off the stage and said that’s the first time that’s ever happened.”

“It was a challenging space and we’re very happy with the result,” beamed Damian Juhasz. “The coverage is excellent, and the performance has been verified independently by the consultant.” Bill Karaitiana concurred; “We’ve had a long involvement with L-Acoustics over 10 years. The support they and Hills provide is exceptional. L- Acoustics have a direct involvement in everything they do. They provide not only a sound system, but an experience.”

Bil Karaitiana

Bil Karaitiana

 

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