I recently rebuilt a headset for a head tracker mouse for a paraplegic chap.
This instructable contains a bit of information that might help anyone else trying to do the same.
The unit that this headset works with is the PRC Headmaster, Prentke HM-2P. Its a fairly old design but it is based around ultrasonic transducers and time of flight calculations.
3D printed using PET+ (tough and flexible).
STLs on Thingiverse or attached