We used to do the party volume test trick. Well that is, we did it on parties, not on gigs. We would graduattelly move up the volume until everybody was screaming their lungs out. Then in a second we lowered the volume completely. People get a bit embarrassed when they scream and everybody can hear them. We always saw people all of sudden start to whisper and looking a bit around them. then we would put the volume back to a normal level. Ah well, maybe not really a practical approach when doing gigs, it might be your last performance there, but I thought I just share an old story here...

I'll be back...