~THE EQUIDOME, A PERSONAL SPATIAL
REPRODUCTION ARRAY
James L Barbour
PhD candidate and audio research
RMIT University of Technology
Melbourne, Australia
ABSTRACT
Research into spatial sound requires the use of a speaker
array capable of reproducing sounds around and above a
listening position. Different arrays have been developed
which are often limited in their accuracy due to room size,
the number of speakers employed and their positions. They
are also expensive to develop which restricts access for many
researchers. A unique array, The Equidome, has been
developed with speakers around and above the listening
position and it uses audio software capable of locating a
sound anywhere over the array, and moving a sound
throughout the array. The Equidome is a personal research
facility capable of 3D spatial composition with mono, stereo,
multichannel or ambisonic source files and reverberation
software is also utilized to create immersive soundfields
throughout the array.
1. INTRODUCTION
1.1. Research objectives
Research into spatial sound recording and reproduction has
led many researchers to develop loudspeaker arrays capable
of generating a three dimensional soundfield at a listening
point inside the array. These arrays have loudspeakers
mounted on the horizontal plane, with other speakers mounted
above and below the listening position, in a variety of
geometrically defined or arbitrary locations. The simplest
might be a four speaker tetrahedral array with the listening
position at the centre of the tetrahedron. The ability of a
listener to accurately locate a sound in 3D space relies on
perceptual cues which are hard to generate in an array with a
limited number of speakers.
'Our aural discrimination of spatial position is not so refined
as, for example, our discrimination of pitch, particularly
where the virtual acoustic space is projected on a limited
number of loudspeakers.' Wishart, T., On Sonic Art [1]
There are many 'holes' in the soundfield where accurate
localization is not possible. If, for example, speakers are
mounted on the frontal and median planes overhead, there are
'holes' at the centre of each of the four upper octants.
Increasing the number of speakers improves spatial accuracy
with limitations including the number of speakers available,
the physical mounting of those speakers and the audio
technology necessary to manage playback and distribution.
1.2. Current Technology
The physical positioning of the speakers is also dependent on
the techniques used for creating, recording and reproducing
sounds with various popular techniques including Ambisonics
[2], Vector and Direction Based Amplitude Panning [3] [4]
and Virtual Microphone Control, ViMiC. [5] Ambisonic
principles have been used by many researchers to record and
reproduce 3D soundfields and the speaker arrays designed for
this purpose range from cubic (8 speaker) arrays to very large
arrays with more than 100 speakers. An example of a small
array in a room of limited size is the ARUP SoundLab [6],
while The Sonic Lab at SARC in Belfast [7] can mount
speakers in multiple layers above, around and below the
listening position using theatre rigging systems and a floating
grid floor, see Figure 1.
Figure 1: The Sonic Lab at SARC
Auditoria with fixed seating usually do not have the capacity
to position speakers below the listening position, but can
successfully stage multi-channel performances with flexible
speaker mounting around and above the audience, and
examples include the Rymer Auditorium at the University of
York [8] and the 22.2 HDTV facility at NHK in Tokyo [9].
Many research facilities have developed diffusion systems
with multiple speakers capable of being assembled in a
variety of configurations around an audience in different
performance venues or outdoors, sometimes with the capacity
to fly speakers above the audience also, including a 32
speaker system developed by SIAL Sound Studios at RMIT
University in Melbourne, [10] and the diffusion system,
BEAST, developed by the research group at the University of
Birmingham. [11] The acoustic properties of the space may
392 2013 ICMC
