To get the best placement of a sub in a pub you need to get in before opening.
Put your sub in the middle of the dance floor designated area. I say designated because it could well be a dining area during daytime.
Play some music with a little booty in the bottom. It doesn't have to be loud, only discernible.
Check out the possible actual locations for the sub for best bass thump. When the sub is swapped in there and cranked up, hey presto, thump on the dance floor.