Cone of ancient New Zealand tree inspires "master stroke" of acoustic design
A humble pine cone has become a source of inspiration for ensuring high speech intelligibility in New Zealand's highest court.
The walls and lower ceiling of the new Supreme Court building in New Zealand’s capital city, Wellington, are covered with spiral shaped acoustic diffusers inspired by the twirls of cones produced by the country’s famous ancient native tree, the Kauri.
Institute of Acoustics members Glenn Leembruggen and Mark Hanson were recently involved in a project to design the acoustics of the orb shaped courtroom in the complex that was officially opened by HRH Prince William earlier this year.
Although based in Australia, Glenn regularly travels to the Institute’s Reproduced Sound conferences in the UK – an annual event where electro-acousticians, acousticians, loudspeaker manufacturers, contractors and end-users share the latest information on the cutting edge of modern audio and electro-acoustics.
The orb shaped courtroom in New Zealand initially proved a challenge as the egg-like curved surfaces would produce “weird sound amplification effects when anybody spoke”, said Glenn and Mark, both principals of ICE Design Australia.
“The curved surfaces of a dome or ellipse can cause sound to focus at specific points in the room, and this focusing creates weird and uncomfortable sounds with speech. One hears their own voice come back, or the voice of another much louder than they would otherwise,” explained Glenn.
“This elliptical room was therefore a prime candidate for this problem, and given it is a room whose primary purpose is speech, this would have caused grave problems for court proceedings.”
One solution to remove the sound focusing problem is to use a “huge” amount of acoustic absorption on the curved walls and ceilings.
However, this approach would pose another problem: using large amounts of acoustic absorption would render the ambience of the room “too dead and would not provide a sense of space or grandeur for NZ’s highest court”, said Glenn.
Another solution is diffusion, which in this circumstance was the best option, as it would retain the ambience of the space, despite involving complex designing of large surface areas.
To demonstrate the potential problem to the architects, the acousticians modified a lighting software package and used a virtual laser beam that could shine at any area within a model of the courtroom.
“This laser beam simulated a sound wave produced at a range of talker positions and its traces clearly showed how the reflection paths of the beam focused at many listening locations,” Glenn explained.
Architects Warren and Mahoney were shown the sound focusing problems and “came back with a master stroke of design,” he said.
They created spiral-wrapped bands of diamond shaped and angled timber panels that look similar to the NZ Kauri cone.
The courtroom effectively has three ‘zones’ of these spiral shaped panels. The lowest band is reflective and flat to provide some natural reflections for speech; the mid-band is diffusive, with angled panels and some low frequency absorption, while the uppermost band provides acoustic absorption to control reverberation times in the room. The skylight consists of a series of glass blades angled for acoustic diffusion, arranged in a floral motif.
ICE also designed and commissioned a sound system for the courtroom, which uses eight bespoke beam-steered line-array loudspeakers.
“The result is a very nice sounding room with speech being clearly audible, with extremely natural sound and high intelligibility at all listeners,” said Glenn.
The IOA's Reproduced Sound conference is being held from November 18 - 18 at the Wales Millennium Centre in Cardiff.
