~Proceedings ICMCISMCI2014 14-20 September 2014, Athens, Greece
Orchestrating wall reflections in space by icosahedral loudspeaker:
findings from first artistic research exploration
Gerriet K. Sharma, Franz Zotter, and Matthias Frank
Institute of Electronic Music and Acoustics
University of Music and Performing Arts Graz, Austria
sharma@iem. at
ABSTRACT
Can we orchestrate the acoustic reflections in a room within
an electroacoustic composition? Doing so appears promising by using the twenty-channel IEM icosahedral loudspeaker (ICO) and its beamforming algorithms. Based on
two musical pieces, we present initial results from an investigation about the perceived auditory objects. By means
of explorative listening experiments, we bring evidence
that the ICO orchestrates wall reflections. Moreover we
can roughly explain the responses by a wall reflection model
with echo thresholds or by a binaural lateralization model.
1. INTRODUCTION
Holophony [1] can be used to replicate natural sound generators or to excite paths of sound reflection. In particular, the notion of employing sound sources with adjustable
acoustic radiation in electroacoustic music was introduced
in Paris in the late 1980s by a research group at IRCAM.
For this renowned concept study they built "la tim6e" [2], a
cube-shaped loudspeaker with six separately driven channels for the production of freely controllable sound radiation directions. In 2006, a technical in-depth investigation
started at the authors' institute. The result was a twentychannel icosahedral loudspeaker system [3], see Fig. 1.
The 20-channel IEM icosahedral loudspeaker (ICO) emits
sound whose strength is adjustable for different spatial directions. It is capable of providing a correct and powerful
simulation of musical instruments in their lower registers
in all their 3600 directional transmission range. The device
is also suitable for the application of new room acoustic
measurements in which controllable directivity is used to
obtain a refined spatial characterization.
Currently there exist only few comparable systems in the
world: a 120-channel system at CNMAT, Berkeley [4],
a 12-channel system at ITA, RWTH-Aachen, Germany, a
12-channel system at the Acoustics Lab, Ben-Gurion University of the Negev, Israel, cubical 6-channel systems at
IRCAM, France, hemi-dodecahedral 6-channel systems at
the Princeton and Stanford Laptop orchestras [5], and experimental systems in works of Curtis Bahn, Perry Cook,
Copyright: 2014 Gerriet K. Sharma et al. This is
an open-access article distributed under the terms of the
which permits unrestricted use, distribution, and reproduction in any medium, provided the original
author and source are credited.
Figure 1. ICO playing spatial music for a dummy
listener for the systematic investigation. Exemplary
binaural recordings of stimulus 2 are available at:
http://iaem.at/Members/zotter/KK_2.wav
and Dan Trueman [6]. Except for the systems in Berkeley,
Princeton, and Stanford, most systems employing spherical beamforming are primarily used for measurement purposes.
The application of the beamforming algorithm developed
in [3] allows strongly focused sound beams to be projected
onto floors, ceilings, and walls. Thanks to the increased
number of loudspeakers, it achieves sound beams that are
three times narrower than early prototypes. The beamforming allows to attenuate sounds from the ICO itself
while sounds from acoustic reflections can be emphasized.
Beams are not only freely adjustable in terms of their radiation angle, also different ones can be blended, or their
beam width can be increased. A loose idea behind employing such sound beams in music is to orchestrate reflecting
surfaces, maybe yielding useful effects in the perceived impression.
It came as a big surprise that the ICO permits to form
three-dimensional auditory objects in space including a useful gradation of depth that was not only noticed by the
composer, but also noticed in statements of fellow artists.
These three-dimensional auditory objects, although more
general, are extensively discussed and pursued in the recent artistic research, e.g. [7].
This contribution is arranged as follows: Section 2 introduces the main questions induced during early performances of the ICO. The subsequent section presents a first
step in answering these questions in terms of an exploratory
auditory evaluation. The results of the evaluation can partly
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