This image shows the listener facing the two loudspeakers. The listener is wearing a black elastic headband upon which is mounted an electromagnetic motion tracking device (a Polhemus ISOTRAK), visible as a small blue box atop the listener's head. The motion tracker is implemented as a transmitter/receiver pair; the receiver is on the listener's head and the transmitter is mounted on the bar spanning the two speaker stands.
Position information provided by the head tracker is used to steer the "sweet spot" of the 3-D audio system to the current position of the listener. Thus, as the listener moves about or rotates his head, the 3-D illusion is maintained. The system can render sources to the front, sides, or behind the listener. Because the sources are externally stationary during head motion, dynamic localization cues are enabled.
The current prototype system renders a single sound source at 32kHz sampling rate in realtime using an SGI Indigo2 computer (25% CPU). The binaural synthesis and crosstalk cancellation could be implemented more efficiently. Future development will concentrate on efficient implementations and the integration of visual head trackers.