It seems a shame that people were turned away from the singarounds. Could you maybe introduce a nominal fee/contribution, payable on the door, for those without wristbands who would appreciate the singaround and maybe even contribute by singing themselves.

Some large mirrors carefully positioned may help to reduce the 'chimney effect' in the room. Not sure how practical or costly that would be though.

I remember the great singarounds in the Mill at Miskin and as far as I can remember they weren't scheduled or formally run, they 'just happened' and developed their own life as the weekend evolved over the years. One thought may be to provide the building, advertise it widely as the place to meet for a singaround and just see what happens. A limited bar in the room and some loo facilities a bit closer may also add to the appeal.

Chris