The suggestion for sealed box speakers is a good one, in my experience. I've got a room of similar size, and had good luck with a pair of little Spendors (forget the model), and I'm back to using my beloved Celestion SL-700s. It took about eight months, but I finally got 'em positioned just right. (Long wall, about a foot and a half from the rear of the speaker to the wall.) I tried several ported designs, but couldn't get any of them to work in that room.
Good luck.
-- Howard
Good luck.
-- Howard