[dmi]

Not a bad option for a lecture theatre, but it's worth noting that IR is line-of-sight and can be easily interrupted by people moving or the receiver twisting as you shift position. Multiple emitters can help with some of this, but there are still challenges.

[ErroneousBosh]

I'll try and get a pic of the setup next time I'm down there. There are these kind of pyramid domes in the ceiling with emitters.