Use low-frequency ultrasound to measure position;
Sound produced by a fixed triangular source (speakers);
Number of sources grows with the tracker work envelope;
The receiver is triangular and attached to the tracked object and has three microphones;
Distance is inferred from the sound time of flight;
Sensitive to air temperature and other noise sources;
Requires “direct line of sight”;
Slower than magnetic trackers (max 50 updates/sec).