how big a speaker can you put in an 11 x 11 room?

Great point Dwhitt - Arros are great, especially with Jazz on vinyl, the OP's stated affliction of choice. Would also throw in a suggestion for one of the Kef monitors - I think the XQ series unless you plan to spend way more for the much better Reference. I owned some of their older low end ones and they were pretty amazing for the price in small rooms. Another to consider, is Usher series, they tend to throw a great soundstage in cramped quarters, not an easy feat.

How big is the doorway? You could put Elipsa's in there but it would be a waste. I would think you would be best served by a sealed box monitor that doesn't go much below 60-80 hz and use a high quality sub that offers a lot of eq adjustability like some of the Velodynes. A huge speaker in a room that size, and square besides would be a waste of money and time.

"A huge speaker in a room that size, and square besides would be a waste of money and time. "

No doubt.

You're getting some good advice and some terrible advice, which is what happens when one shouts out a question in the mall parking lot that is Audiogon.

The square room, even with the 6 ft. vent, creates a special problem because of the extreme room modes it is probably creating (exact effects depend upon furnishings, room construction, and other factors). Simply put, it will cause some bass frequencies to be exaggerated and others to be deemphasized. To address this, you will need a speaker with adjustable, powered bass, or monitor speakers augmented by a subwoofer, along with a lot of patience to try various set-ups in your room.

The room is also small, which rules out many midsize and all large speakers. Putting a large speaker in a small room that is also square is a recipe for absurdity (Salon 2's, which have prodigious bass, in a room that measures 11' x 11' x 8' would be an terrible move, as would Studio 2's).

One good, reasonably sized speaker with adjustible, powered bass is the Vandersteen Quatro (there are of course others). There are a lot of good monitors and subs out there. If you like the Revel sound, Gems and a Revel B15 would work and make you happy.

Hey...I mentioned totem arro's!