Alternative Voices for Electronic Sound: Spherical Speakers and Sensor-Speaker Arrays (SenSAs)

We describe several recent applications of spherical speakers (multi-channel, outward-radiating geodesic speaker arrays) and SensorSpeaker-Arrays (SenSAs: combinations of various sensor devices with spherical speaker arrays). We discuss the design and construction of these systems, and, more generally, the new "voices" they give to electronic sound. Introduction Arrays of widely spaced mono-directional loudspeakers (P.A.-style stereo configurations or "outside-in" surroundsound systems) have long provided the dominant paradigms for electronic sound diffusion. So prevalent are these models that alternatives have largely been ignored and electronic sound, regardless of musical aesthetic, has come to be inseparably associated with single-channel speakers (often in relatively high-volume contexts), or headphones. We recognize the value of these familiar paradigms, but believe that electronic sound can and should have many alternative, idiosyncratic voices. Through the design and construction of unique sound diffusion structures, we can reinvent the nature of electronic sound; when allied with new sensor technologies, these structures offer alternative modes of interaction with techniques of sonic computation This paper describes several recent applications of spherical speakers (multi-channel, outward-radiating geodesic speaker arrays) and Sensor-Speaker-Arrays (SenSAs: combinations of various sensor devices with outward-radiating multi-channel speaker arrays). Spherical speakers have long been applied in the study the acoustic qualities of performance spaces (see, for instance, Hidaka and Beranek, 2000) and instruments (Causse et. al., 1992; Roads, 1996; and Wessel, 1991). More recently, building on previous studies of the directional radiative properties of acoustic instruments (the NBody Project; Cook and Trueman, 1999), they have been used in performance to reproduce some of the diffusion characteristics of conventional acoustic instruments; spherical speakers engage the reverberant qualities of their performance spaces and allow electronic and acoustic instruments to blend readily. After custom-building several spherical speakers by hand, we began working with the U.S. Enclosure Company to produce over a dozen spherical speakers of varying sizes ranging from 8-inch to 14-inch. We will detail their use in the performance and recording of two works by composer Steven Mackey: a concerto combining electric guitar and digital signal processing with full orchestra, and a composition for string quartet and liveelectronics/electric guitar. The electronic improvisation ensemble "interface" (Bahn and Trueman) has integrated a family of these spherical speakers into their standard setup, completely replacing their previous P.A. diffusion model; as we discuss, this has encouraged us to substantially reinvent our approach to the performance of live interactive computer-music. This presentation introduces a large new 22-inch diameter SenSA (Bubba) motivated by the first SenSA, the Bowed-Sensor-Speaker-Array (BoSSA; Trueman and Cook, 1999). The two SenSAs have been used together in performance to realize a new approach to electronic chamber-music. BoSSA has also motivated several new works for interactive dance performance systems and SenSA. Finally, we are exploring the use of spherical speakers and SenSAs in installation art, using the directional capabilities to create more compelling sonic experiences in open and closed spaces. We describe the design and construction of these systems, and, more generally, the new "voices" they give to electronic sound. Electronic Sound in Conventional Acoustic Ensembles Combining acoustic instruments with electronic sound is a notoriously difficult problem. By subtly amplifying the acoustic instruments and adding a judicious amount of artificial reverb, we can often succeed in bringing their sound into the electronic realm, creating a virtual electronic space. While good for many applications, this approach usually has the effect of negating the natural acoustic qualities of performance spaces and can make it difficult to localize the acoustic sources (“I can’t tell who is playing what,” is a common complaint—this may be desirable, but should not be inevitable). As the size of the acoustic ensemble grows (especially to orchestral proportions), it becomes increasingly difficult to absorb it into the virtual electronic space—acoustic and electronic sources begin to separate, like oil and water. Finally, this approach presumes that electronic sound is intended exclusively for performance (projecting outwards), and is not a solution if we are interested in making a kind of electronic chamber music, where the social/acoustic context of music making is of primary importance (and performance secondary). From our work studying the spatial radiative timbral qualities of acoustic instruments (NBody), we have found that spherical speaker arrays offer a compelling alternative. Since they radiate sound spherically, these speakers engage the reverberant qualities of performance spaces similarly to acoustic instruments. They also localize well, and provide an approach that does not assume performance (they are remarkably successful in small, chamber music contexts). With this approach, we invert the previously described technique by bringing the electronic sound into the