Reply to Subwoofer size to rock any bar.

Im lookin for a woofer that will be powerful enough to fill most average bars with bass. Obviously cubic ft will come into play but i wont be playing at large clubs. I want the people to know its there not just barely be able to fill a room. Theres 18" and 15". how many watts would be sufficient to get the job done and have extra to play with.

This is a noob question. Im not looking for that perfect sub power from anyone just a general watt and speaker size some of you use for medium to large bars.