Mess around with EQ and reverbs. I find trial and error best.
You can download
"club" sounds for free. http://www.freesound.org/samplesViewSingle.php?id=38938
Something like that. Background noise is key.
With regards to reverb, using
something like "large hall" preset isn't probably the best idea. Very few people would
hear a PA blasting out a song in an empty hall (unless thats whats going on in the film!).
Lots of people = way less reverb. So i'd say a slightly smaller room sound than what you'd
initially think. Or at least a smaller reverb time.
Maybe a really subtle
EQ wise, I don't know cause i've never tried it, but i'd probably do
what i wouldn't do if i was mixing it if that makes sense! Take out some of the clarity
from upper mids/highs. Take out some of the tighter bass and boost in the lower bass. So
it sounds a bit more boomy. Just trying to muddy it up a bit. Although after running it
through a reverb I doubt it will need to much.
Doesn't take long to mess with a
few EQ settings to see what you can come up with.