Optimal speaker size for given room, or drivers?

How do I determine what speaker size to buy and how many drivers are appropriate for my room? My room is 14x22, with an opening at the back into a hallway. I also have another 6x8 foot arm toward the front. Ceilings are an average of 9 feet tall. Listening position will be 13 feet from the front, speakers 4 feet from the wall and 8 to 9 feet from each other. I can't try any of these at home without committing to a purchase.

Considering a full range like the B&W 802d, Thiel 3.7, Tyler Decade D1 or D2, or Sonus Faber Cremona M. These are examples of the size I am looking at, not speakers I have settled into (I have only heard the 803s, Cremona and older 3.6, for example). Something not too big (150lbs or so) and full, but not overwhelming. This isn't a long-term house for us and although a larger speaker would sound fine in this room, I may be using them in a smaller room in the future.

Some of these speakers feature many drivers and midranges, such as the Tyler D1, whereas others such as the 802D are essentially 1 midrange and 1 driver. The Cremona M is somewhere in the middle. What are advantages and disadvantages to each type of design? Is a larger array more complicated and harder to pull off, or is it simply a matter of cost of manufacture?
The questions you've asked are very complex and would require a book (more likely several books) to address properly, not a few paragraphs in this forum.

What further complicates it is that you may change to a smaller room in the future but you're not sure when and you have no idea what size the other room will be.

A speaker with strong and extended bass performance might work well in your present room but may totally overwhelm a smaller room and sound terribly unbalanced.

If I were in your shoes, I'd concentrate on getting good sound in my present room and if I had to sell the speakers in the future to get good sound in a different room then that's what I would do.

How many drivers a speaker has is probably not that relevant to your particular situation. Anything from a single-driver speaker to a multi-driver line array could work well in your room... depending on your listening biases, associated gear, aspects of room acoustics, etc.

In other words your questions are far too vague to be answered with any certainty. Perhaps others could suggest some informational links for you. My view is that there's no substitute for a little trial and error. At least that way, your preferences will be based on your own experience and not somebody's opinion which may or may not represent your needs.

And besides... rooms are almost like fingerprints... each one has its own acoustic wrinkles.

Maybe you should simply buy decent but robust monitor speakers (or any decent speakers) that don't have significant output below 80Hz. Then you could fill in with a subwoofer or two and only change the subwoofer(s) if necessary, when you move.

To be more specific would be like a blind man trying to discribe a scene he's never seen.
Your current listening room size is very close to mine. If you want a full range speaker that could work well in your current room and still be appropriate for a possible future smaller room, I recommend you consider the Vandersteen Wood Quatro's. They are exceptional speakers that are in your apparent approximate price range, and have the advantage of being tunable to an individual listening room's "needs." They were the speakers I was going to purchase until I heard the Sonus Fabers. It was a tough choice, but for me, the Sonus Fabers won out overall in terms of musicality and involvement. However, if I thought I would have needed to place the speakers in a significantly smaller room in the future, I probably would have purchased the Quatro's. Although I found them to be a bit less musical and involving than the Sonus Fabers, I have never heard a speaker that images better than the Quatro's.
Best you find a dealer that will let you borrow demo speakers, otherwise it is a crap shoot. Nothing, and I mean nothing is a substitute for listening in your environment with your equipment driving them, and your favorite music playing. Acoustic wrinkles in your listening space, as noted, will play havoc with 'buying on paper', or the dealer's room. Dealer demo's are typically 'broken in' and often they come with cables that the dealer has found make them shine. In over five decades of being involved in audio, I have never purchased a speaker that was not provided as a demo to try in my 'chain/enviroment'. Interestingly, in most cases I purchased the demo's at a nice discount. Two weeks should be the amount of time needed for you to make a judgement. In these economic times, dealers are going the extra mile to make sales, so take advantage of it. Hey, with gas at $1.50 you can make 'sleping' pay.
The most precise soundstage is achieved with a point source. This means one midrange and one tweeter. Multiple drivers are only acceptable in the bass, where wavelengths of the sound are very large). A very pleasant wall of sound can be achieved with an array or an MTM configuration but it won't image quite as effectively and you may find differences between a seated and standing position. (drivers operating over the same frequencies cause lobbing - you get lines of stronger sound and lines of weaker sound as the signals from each driver interfere)
4musica44107 writes:

"Although I found them to be a bit less musical and involving than the Sonus Fabers, I have never heard a speaker that images better than the Quatro's."

My NSR Sonic Research Sonata D3 speakers image considerably better than my friend's Quatros... The D3s also sound more immediate, detailed, and dynamic. They would work well in your current room, but not in a much smaller room. That said, I believe the designer John Tabernacki will be coming out with smaller models that use the same technology sometime in 2009.

The Quatros are definitely darker in the upper midrange (steeper rolloff) than the NSRs, which is likely responsible for the NSRs sounding more vivid, lifelike, and detailed. The NSRs are also considerably more articulate in the bass.

Disclaimer: As with most comparisons made in this forum, my above comparison of the Vandersteen Quatros to the NSR Sonata D3s was made in two different listening rooms, with two different sets of associated gear, and on different days. So the comparison may be entirely valid or entirely invalid. In any case, it was based on my actually hearing both systems with familiar recordings.
I second the Quatro's my dad owns the wood signature model and his room is close enough in size to be comparable and while nobody can predict how any given speaker will perform the Vandy can be tuned to sound great in most any application.......that I can say for sure.
Vandersteens are as dark as whats around them from Pre, to Amps, cables and source, they are a pretty honest speaker with a touch of warmth that is rarely called a negative.
Find a dealer that will let you bring them home....

All of the speaker you listed should be ok ( some better than others). A word of caution about the 802Ds. They need a lot of space to sound ballanced. They tend to be a little boomy and they can get very boomy in small rooms. Now in the right room with the right gear they can sound great.
Vandersteens will likely be smoother and no doubt much less problematic with bass in room adjustability.