L-Acoustics tames Brisbane City Hall
AUSTRALIA: An L-Acoustics system primarily based on Kara enclosures with SB18 subwoofers has been used to counter the historically difficult acoustic properties of one of Brisbane’s most iconic buildings. Since its opening in 1930, Brisbane City Hall immediately became, and has remained, the backdrop to many of the city’s cultural and social activities. However its famous circular main auditorium, which seats 1,600 and includes a 120-year old Father Henry Willis organ as its centrepiece, has long proved acoustically challenging.
Following the completion of a AUS$215 million refurbishment that took place between 2009 and 2013, attention turned to improving the sound of the auditorium, and a tender was issued. Australian L-Acoustics distributor Hills alongside systems integrator Con-Sol worked with the French manufacturer 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 design 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,’ explained Damien Juhasz, systems engineer at Hills. Regarding the acoustic difficulties of the venue, L-Acoustics application engineer Germain Simon added, ‘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’.
The selected design is based on a left-right configuration with 10 Kara enclosures flown per-side, augmented in the low frequencies by two SB18 subwoofers per array. Additional low frequency reinforcement is provided by a central block of four SB18 subs which are ground-stacked under the front of the stage.
‘We focused a lot of effort on the sound levels, achieving a great result by flying the main system a bit higher than originally planned,’ revealed Mr Simon. ‘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.’
Additionally, the main system is supplemented by a stage-lip front-fill comprising 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, while six 8XT coaxial enclosures act as a distributed monitor system around the stage lip. Power for the installation is via LA4X amplified controllers, which also provide signal routing and DSP.
Added an extra level of complication, meanwhile, was the fact that the building’s existing speaker cabling infrastructure was incapable of meeting the requirements of the L-Acoustics 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,’ explained Mr 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.’ Finally, the integration of the City Hall’s existing voice alarm system into the main PA was achieved via the use of a control system from Crestron.