Well, the obvious solution is to play so loud that people have no choice but to either listen or go to the bar - although I'll admit that that might not be a workable option if you're the Cowboy Junkies.
This is why I refuse to go and see Sunn O))). What's the point of paying all that money for a ticket if you can't hear yourself chat?
Conversations at Sunn 0))) gigs are often delivered through the medium of mime and interpretative dance...or by lip reaing "Sorry, I can't hear you. LoL".