Instead of placing a number of loudspeakers in separate locations to achieve stereophony, surround sound, or simulations of room information, we are developing a loudspeaker system that is concentrated in a small and single location and that has a programmable radiation pattern. It is the computer instrumentalist's sound source.
One motivation for this idea comes from a number of frustrating experiences with chamber music that mixes electroacoustic and traditional acoustical instrumental sources. Here the acoustical instruments are unamplified but the electronic part is passed through a stereo or quad system. The usual result is that the electronic part and the acoustical instruments sound as if they are operating in entirely different acoustical spaces.
The system is an amalgam of digital signal processing and loudspeaker technologies. The system allows for time-variant control of the polar radiation pattern as a function of frequency. It can also simulte the radiation characteristics of acoustic instruments that vary in dramatic ways with the musical materials.
A look at the literature on acoustic instrument radiation (for a summary see [Fletcher and Rossing 1991] ) shows that the polar radiation patterns vary considerably as a function of frequency. Furthermore, the nature of this variability is different across the various instruments. This is true not only for musical instruments but also for other natural sound sources. One is also struck by the fact that conventional loudspeaker radiation patterns are much more homogeneous than those of the acoustic sources. Indeed, much effort has gone into the design of speakers so that they behave in this more neutral manner. Furthermore, conventional loudspeakers, when viewed across the spectrum, are much more directional than the majority of natural sound sources.
This type of speaker system is not a replacement for the stereo or surround-the listener approach. It is as a compliment to these approaches with some special advantages. Such systems allow the computer musician to perform in an acoustically compatible manner with traditional instrumentalists. As we approach portability performers can take fuller responsibility for their sound, facilitating that more personalized sound that I have argued for earlier. The synthesist can specify the time variant radiation pattern behaviors in a way that is tightly coupled with the synthesis algorithm. Finally, there is a social implication. As these systems develop they will help resolve arguments between "acoustic" and "electronic" performers and stimulate the development and performance of an intimate and mixed music that would thrive in small private and public spaces.
Our first cubic array prototypes built from commercially available powered speakers:
Our latest prototype dodecahedron:
Here are some images from the construction of our dodecahedral loudspeaker.
Fletcher, N.H., and T. D. Rossing. 1991. The Physics of Musical Instruments. New York: Springer-Verlag.