Parliament House Darwin - Intelligibility with NEXO Geo S

The Grand Hall of Parliament House in Darwin is indeed a Grand and Beautifully designed building.

The interior and public areas of the building and in particular, the Grand Hall is constructed and finished with materials such as Mount Bundy and South Australian Granite flooring, White polished wall panels, and attractively arranged Tasmanian Golden Sassafras wooden panels. Collectively, with symmetrical lines, high ceilings, robust columns and natural light entering from the terrace windows the People's Hall is undoubtedly an ageless architectural work of art.

Entrance to the Hall is via the front Forecourt and foyer. The Hall forms the central focal area of the building, overlooking the Speaker's Green Terrace and beyond, a spectacular view of Darwin's natural Harbour can be seen through the large glass window structure.

Despite the aesthetic appearance of the Hall, acoustically the room is very reverberant. Across the audio spectrum, and in particular at speech frequencies, the Reverberation time Constant (RT60) is as high as 3.1 seconds @ 1kHz. This poses intelligibility problems when sound reinforcement systems are used during public gatherings and functions that are regularly held in the Hall.

Investigations by local Audiovisual / PA Company Audio Technology NT Pty Ltd, revealed that it wasn't so much the reverberation that caused the speech intelligibility problems, but more so the opposing parallel, polished surfaced walls and Granite floors that contributed to multiple and non-diffusing, destructive reflections that resulted in 'interference' or loss of articulation at the listeners' ear level.

An earlier Acoustical investigation report suggested that to achieve the desired result of speech intelligibility in the Hall, a special loudspeaker system was required that exhibited High Directivity, provided full coverage of the audience area and a method to possibly reduce the reverberation time.

The desire to rectify the problem was significant enough for the client to seek estimates to improve the acoustic properties of the building such as lowering the High Ceiling and treat with sound absorbing material; an exercise that proved to be prohibitively expensive.

Audio Technology NT Pty Ltd was commissioned to evaluate the acoustic environment and install a system that would provide Speech intelligibility that was 'natural' sounding, provide speech localization and provide uniform sound pressure level within the Grand Hall.

After extensive evaluation of the Hall, and research into the available speaker technology, Audio Technology chose to install the Nexo Geo – S system. This system was found to be the most suitable system that was capable of providing the criteria stipulated by the acoustic consultant, and achieve the desired results.

In conjunction with the Nexo Australian distributors, Group Technologies – A System comprising two arrays of 5-element 805/30 enclosures was designed, to be suspended 7m above the ground floor of the Hall.

Although the Hall is rectangular in shape, most of the speeches and presentations are given from the centre of the North Side wall, closest to the Chamber Entrance. This required the two vertical arrays to be angled in 50 degrees from their suspension points, on the two extreme columns of the Hall.

Each array consists of 3 x 805 (5 degree) elements and 2 x 830 (30 elements)

The arrays are tilted 15 degrees to achieve the simulated results predicted by Geo Soft. The loudspeakers are driven by a Camco Vortex 6 amplifier, and Nexo NX241 Processor.

The two arrays provide excellent sound coverage over the 550 square metres. The quality and clarity of sound is very impressive, and almost 'unbelievable' considering the poor acoustic environment. In order to blend in with the décor, the loudspeaker cabinets and frames were painted white prior to installation.

The Geo S system achieved the desired goals of localized speech reproduction with excellent intelligibility and clarity.


Grand Hall Parliament House Darwin


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