You have a large room and asking an awful lot from a 12" sub. If you are only going to go with one sub, then you shouldn't look at anything smaller than 15". If you are going to stick with a 12" sub, then you need to add a second one. You could possibly place the second sub on the wall that's between the hallway and the fireplace. If you do get a second sub, you have to make sure that the two subs place nicely together and are not canceling each other out, and make sure that you integrate them with the rest of your speakers. Once you add the second 12" sub, then you might achieve what you are looking for.