  This paper presents the interface developments and music of the duo
"interface," formed by Curtis Bahn and Dan Trueman. We describe gestural
instrument design, interactive performance interfaces for improvisational
music, spherical speakers (multi-channel, outward-radiating geodesic speaker
arrays) and Sensor-Speaker-Arrays (SenSAs: combinations of various sensor
devices with spherical speaker arrays). We discuss the concept, design and
construction of these systems, and, give examples from several newly published
CDs of work by Bahn and Trueman.
