The range of the signal depends on the characteristics of the speakers, the volume they're playing at, and the layout of the room. With the right speakers and good positioning you should be able to cover auditoriums and other large rooms.
Besides the troubleshooting guide, there is also this document, but it doesn't cover the ultrasonic aspect of this in any depth: https://projectworkplace.cisco.com/assets/pdf/proximity-networking.pdf
