ORCHESTRATING SPACE BY

ICOSAHEDRAL LOUDSPEAKER

[OSIL]


THE NOVELTY IN OSIL in contrast to common surrounding loudspeaker systems lies in controlling the strengths of the wall reflections that could be excited from a single performer’s location. Namely an icosahedral loudspeaker is employed as an instrument of adjustable directivity at this location.

In electroacoustic music, the notion of adjustable-directivity loudspeakers was introduced in Paris in the late 1980s by researchers at IRCAM. For the renowned concept study “la timée” [WDC97], a cube housing six separately controlled loudspeakers was built to achieve freely controllable directivity. Despite the ingenious idea and theory, loudness and focusing strength weren’t convincing enough to be employed in concerts. In 2006, researchers at IEM (University of Music and Performing Arts Graz) reconsidered theory aiming at an acoustically correct and powerful reproduction of musical instruments in their lower registers, including the entire 3D directivity pattern. The resulting icosahedral loudspeaker (IKO) is more powerful, of larger size, and larger number of loudspeakers. Moreover, a success in quality was achieved by reconsidering algorithms and acoustic calibration to control sound beams [Zot09] that are three times narrower than beams of earlier systems.

COMMON SPATIALIZATION SYSTEMS for computer music employ loudspeaker arrays that surround the listening area, such as the BEAST (University of Birmingham), the Espro (IRCAM), the Klangdom (ZKM), the CUBE and the MUMUTH (KUG). They either use the psychoacoustic phenomenon of a phantom source [Wen63, Pul97] to create auditory objects between the loudspeakers, e.g. VBAP  and Ambisonics [Ger73, Dan01], or aim at recreating a physically accurate sound field, e.g. wave field synthesis [Ber88, SRA08].


The quality assessment of such systems is a current research topic [Fra13a, SWR+13, FZWS14, LEL+14, MZF14]. To a certain degree, these systems assume anechoic listening conditions and their accuracy suffers from reflections.

 

THE IEM ICOSAHEDRAL LOUDSPEAKER (IKO) consists of an icoshaedral housing carrying 20 individually driven loudspeakers and has been built in 2006, originally with the idea to holographically mimic musical instruments.

THE HISTORY OF THE IKO

     m a i n p a g e

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an acoustically correct and powerful reproduction of musical instruments in their lower registers, including the entire 3D directivity pattern. The resulting icosahedral loudspeaker (IKO) is more powerful, of larger size, and larger number of loudspeakers. Moreover, a success in quality was achieved by reconsidering algorithms and acoustic calibration to control sound beams [Zot09] that are three times narrower than beams of earlier systems.


Except for the 120 channel array at CNMAT [AFKW06] that runs Zotter’s algorithm (from 2007), none of the few comparable arrays is employed with similar goals or algorithms (12 channel system at ITA RWTH-Aachen [PB09], 6 channel and experimental systems Stanford/Princeton [TCSW06, CETT98]).


Other than spherical arrays, a number of linear loudspeaker arrays is being sold for home theaters to simulate side/rear loudspeakers through wall reflections (Yamaha YSP series, BOSE VideoWave®). Planar, parametric arrays Acouspade and Audio Spotlight are being sold and are able to create the narrowest sound beams. However, spherical arrays are currently more flexible and more powerful.

THE IKO TRULY PERMITS TO FORM THREE-DIMENSIONAL AUDITORY OBJECTS IN SPACE. Its strongly focused sound beams can be projected onto floors, ceilings and walls, while direct sound from the IKO is often attenuated so that rather sounds from acoustic reflections become audible.


Beams are freely adjustable in terms of direction. As alternative ways to spatialize, different beams can be blended, or their beam width manipulated. Spatial auditory objects created by the IKO can be moved around towards the reflecting surfaces or collapse onto the IKO. What is more, objects can be composed as to include useful gradation of depth, which was recognized by the audience, according to feedback statements.

Early Performances and Inquiries: grrawe and firniss

As a result of this fruitful composer acoustician dialogue, the compositions grrawe 2010 (10’26’’) and firniss 2012 (11’23’’) could be developed. These two pieces were stepping stones to thinking about the technical device and its acoustical principles as a means of artistic expression and orchestration of sounds in space. grrawe and firniss were invited to a number of conferences and concerts. grrawe was presented within the context of the Forum Alpbach 2010 and formed part of the concert program at the Digital Audio Effects Conference DAFx10, as well as at the 2011 “next generation” Festival at the Center for Art and Media Technology ZKM Karlsruhe. Franz Zotter and Gerriet K. Sharma’s work with the IKO was the only Austrian contribution presented in the music category within the framework of the ELIA-Art Schools NEU/NOW Festivals 2011. The IKO and grrawe were presented to a specialist audience of composers and sound engineers at the International Conference for Spatial Audio ICSA 2011. grrawe & firniss were invited to the International Computermusic Conference ICMC 2012 and the Internationale Ferienkurse für Neue Musik Darmstadt 2014.
It first came as a lucky surprise that the IKO truly permits to form three-dimensional auditory objects in space. Its strongly focused sound beams can be projected onto floors, ceilings and walls, while direct sound from the IKO is often attenuated so that rather sounds from acoustic reflections become audible. Beams are freely adjustable in terms of direction. As alternative ways to spatialize, different beams can be blended, or their beam width manipulated. Spatial auditory objects created by the IKO can be moved around towards the reflecting surfaces or collapse onto the IKO. What is more, objects can be composed as to include useful gradation of depth, which was recognized by the audience, according to feedback statements.

   *[Wen63, Pul97] K. Wendt, “Das Richtungshören bei der Überlagerung zweier Schallfelder bei Intensitäts- und Laufzeitstereophonie,” Ph.D. dissertation, RWTH Aachen, 1963. // V. Pulkki, “Virtual sound source positioning using vector base amplitude panning,” J. Audio Eng. Soc, vol. 45, no. 6, pp. 456–466, 1997.
    *[Ger73, Dan01]  M. A. Gerzon, “With-height sound reproduction,” Journal of the Audio Engineering Society, vol. 21, pp. 2–10, 1973. J. Daniel, “Représentation de champs acoustiques, application à la transmission et à la reproduction de scénes sonores complexes dans un contexte multimédia,” Ph.D. dissertation, Université Paris 6, 2001.
    *[Ber88, SRA08] A. J. Berkhout, “A Holographic Approach to Acoustic Control,” J. Audio Eng. Soc, vol. 36, no. 12, pp. 977–995, 1988. [Online]. //  S. Spors, R. Rabenstein, and J. Ahrens, “The theory of wave field synthesis revisited,” in Audio Engineering Society Convention 124, 5 2008.
    *[Fra13a, SWR+13, FZWS14, LEL+14, MZF14] M. Frank, “Phantom sources using multiple loudspeakers in the horizontal plane,” Ph.D. dissertation, University of Music and Performing Arts, Graz, 2013. // S. Spors, H. Wierstorf, A. Raake, F. Melchior, M. Frank, and F. Zotter, “Spatial sound with loudspeakers and its perception: A review of the current state,” Proceedings of the IEEE, vol. 101, no. 9, pp. 1920–1938, Sept 2013. //  M. Frank, F. Zotter, H. Wierstorf, and S. Spors, Quality of Experience. Springer, 2014, ch. Spatial Audio Rendering, pp. 247–260. //  A. Lindau, V. Erbes, S. Lepa, H.-J. Maempel, F. Brinkman, and S. Weinzierl, “A spatial audio quality inventory for virtual acoustic environments (saqi),” in EAA Joint Symposium on Auralization and Ambisonics, Berlin, April 2014. // G. Marentakis, F. Zotter, and M. Frank, “Vector-base and ambisonic amplitude panning: A comparison using pop, classical, and contemporary spatial music,” in EAA Joint Symposium on Auralization and Ambisonics, Berlin, April 2014.

   *[WDC97] O. Warusfel, P. Derogis, and R. Caussé, “Radiation synthesis with digitally controlled loudspeakers,” in Papers of the 103rd AES Convention, New York, 1997.
    *[Zot09] F.Zotter, “Analysis and synthesis of sound-radiation with spherical arrays,” Ph.D. dissertation, Univerity of Music and Performing Arts, Graz, 2009.

    *[AFKW06] R. Avizienis, A. Freed, P. Kassakian, and D. Wessel, “A compact 120 independent element spherical loudspeaker array with programmable radiation patterns,” in Papers of the 120th AES Convention, Paris, 2006.
    *[PB09] M. Pollow and G. K. Behler, “Variable directivity for platonic sound sources based on spherical harmonics optimization,” Acta Acustica united with Acustica, vol. 95, no. 6, pp. 1082–1092, 2009.
    *[TCSW06, CETT98] D. Trueman, P. Cook, S. Smallwood, and G. Wang, “Plork: The princeton laptop orchestra, year 1,” in Proceedings of the International Computer Music Conference, ICMC, New Orleans, 2006. // P. Cook, G. Essl, G. Tzanetakis, and D. Trueman, “N>>2: Multi-speaker display systems for virtual reality and spatial audio projection,” in Proceedings of the International Conference on Auditory Display, ICAD, Glasgow, 1998.