Icosahedral Loudspeaker: the ICO as instrument for electronic chamber music (IEM #5)

IEM‘s ICO is a 20-channel loudspeaker, developed by Franz Zotter at IEM. The ICO, and its smaller spherical cousin, was developed as a part of Zotter’s PhD research into sound radiation synthesis as a tool for replicating the acoustic radiation of instruments and measuring the acoustic response of rooms: “This work demonstrates a comprehensive methodology for capture, analysis, manipulation, and reproduction of spatial sound-radiation. As the challenge herein, acoustic events need to be captured and reproduced not only in one but in a preferably complete multiplicity of directions” (Zotter, 2009). The ICO was developed primarily as a technical tool but through collaborations between Zotter and composer / sound artist Gerriet Sharma it has found application as a creative tool, or indeed as an instrument. As Sharma and Zotter (2014) outline “[The ICO] is capable of providing a correct and powerful simulation of musical instruments in their lower registers in all their 360◦ 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.” It is this “controlled directivity” that has primarily found artistic application. The “beamforming algorithm developed in [Zotter’s PhD research] allows strongly focused sound beams to be projected
onto floors, ceilings, and walls… [This] allows to attenuate sounds [sic] 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.”

ICO 20-channel loudspeaker (IEM)
ICO 20-channel loudspeaker (IEM)

My work with the ICO, in combination with the IEM 24-channel hemisphere array, certainly confirmed that beam-forming can find artistic application, and indeed that the phenomena described by Zotter and Sharma are actual (hearing is believing). My exploration of the ICO’s propensities as a compact loudspeaker array are confirmed by small sample listener-response research presented in their 2014 paper. Using spatial controller plug-ins (VST) developed by Matthias Kronlachner it is mercifully trivial to shape and control acoustic beams in terms of perceived size, movement, and to use beam-forming to create reflections on surfaces within the performance space.

It is the latter that is perhaps the most surprising and lively aspect of the ICO (although there’s much to be said for the capabilities of the ICO as an acoustic surface, see below). To my ears this is because it requires one to fully engage with the rich interactions of source material, loudspeaker and room response in ways which one tends not to do when using the hemispherical array (or indeed any other multichannel approach). This is simply because in such arrays one is concerned with creating a virtual sound image/space and concern for the room acoustic tends to be limited to minimising its impact on the qualities of audio reproduction or reinforcement (in the case of live electronic music). Using the ICO as an instrument to “orchestrate reflecting surfaces” on the other hand, requires engagement with the acoustic properties of the performance space as an integral aspect of the creative process, and also an awareness of the specific capabilities of the ICO. The outcomes of this are interesting:

The (electroacoustic) work itself can no longer considered as independent of the space in which it is to be performed. In composing Let x = (2014-) for the ICO and hemisphere, for example, many of the compositional decision made in those sections of the work for the ICO alone were based on achieving results that may not be achievable in other spaces. (I hope I get the chance to find out!) When combining the ICO with the hemisphere this was not the case as the latter masks the acoustic response of the IEM Cube space, making such sections or passages more readily transposable to other spaces. One of the really exciting things about working with the ICO is that you are required to closely tune in to the interaction sound, space and movement, and often encounter results that are quite unexpected as the room response enacts spatial behaviours that could not be anticipated from the topology and morphology of source material projected from the ICO. The room itself is revealed as a sonic object integral to the work as a whole and this raises the very question of what it is to compose spatially.

When one uses the ICO to orchestrate space, or more accurately to orchestrate perceived relationships between sound and space (sound and space being interdependent), one is orchestrating for a specific space, creating a relatively high (but far from total) degree of site-specificity. In moving a work from one space to another, the piece needs then to be spatially recomposed in order to work in a new acoustic context. This is entirely possible, as Sharma wonderfully demonstrated in his Signale portrait concert (11 Nov 2104) in the György-Ligeti-Saal in MUMUTH, which featured works not originally composed for this space. The question arises though: what kind of work, using the ICO and focused on sound-space orchestration, is more readily adapted for effective outcomes in different spaces, and indeed are all spaces suitable for the ICO and such application? (I hope to return to this topic in a later post, including the ways in which the ICO can be used in sound installation work, as it has been by Martin Rumori.)

The ICO, despite its unique affordances, is characterised by a number of limitations. That these are noticeable is due to recognition of what the ICO is as a musical object, rather than a response to the false expectation that the ICO is some kind of super-loudspeaker, possessed of sonic superpowers. In fact, such limitations should lead one to consider the ICO as an instrument which, as is the case in effective use of any instrument, needs to be used in ways that exploit its strengths and are not compromised by its shortcomings (don’t ask a trumpet to do the rapid passage work of a flute, for example). Due to the driver size (16.5cm), the frequency response of the ICO is reduced below around 150Hz and the power of each individual speaker is also limited. These limitations can be overcome by coupling loudspeakers to create greater loudness and improve bass response (the typical solution is to feed low-pass signal below 150Hz to all 20 loudspeakers). However, these solutions have acoustic-spatial implications. Bass material, even in low-mid range, is clearly non-directional when an omni-source is created (as just described), which decouples this frequency range from directional beam-forming producing occasionally quite unusual spatial effects (which Sharma has exploited). Similarly, beam-forming is compromised when loudspeakers are coupled to increase loudness as the signal is spread over a larger area. Moreover, the icosahedron that houses the 20 loudspeakers is itself something of a resonating chamber which, although far from functioning like a resonator in a traditional instrument, has its own acoustic colour.

Beam-forming and sound-spatial orchestration are two of the strengths of the ICO, but I shouldn’t forget that the ICO packs a lot of loudspeakers into a relatively compact object. This comes right down to the possibility to address each loudspeaker individually, creating a very distinct point source. While I was surprised by what can be done in working with the ICO as a tool for creating acoustic reflections, I was equally pleased to hear it realise my ideas for enacting complex acoustic surfaces. Pontillistic textures skittering across its surface, sweeps of material oscillating between indirect and direct loudspeakers, clearly stratified layers of sound, and all emanating from a discrete spatial field. As I hope was evident in Let x = the ICO offers an abundance of spatial-compositional possibilities, even before using it to stimulate and shape room response or conjoining it with a more traditional array such as the IEM hemisphere.

Given the just outlined propensities and limitations of the ICO, it’s my feeling that not only should it be considered as an instrument, but more than this it is an instrument suited to chamber music. After all, in itself it is a chamber, a space which has a certain resonance which gives it the quality of enclosing sound as much as it projects sound. In other words, it has its own sound, it’s own sonic grain, as any instrument does. Through its frequency response and loudness it is best suited for small to medium size rooms, such as those in which chamber music is best heard, not so much because it cannot project sufficiently to be heard in large spaces but more because it requires listener proximity allowing perception of the detail it generates, both in itself and in the space it activates.

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