It's nothing to do with the diamiter of the drivers, but their xmax. If they're farting, they're not very good drivers for bass.
I'd go with flogging it & get something with better drivers. I don't know how loud you play, but I don't get any farting with my Markbass 2x10 combo & I'm certainly not a quiet player (I play DnB & Dubstep basslines).