What makes a speaker too big for a given room?

Wow thats a tough on DUDE!!

FWIW, I have a pair of Dali Helicon 400's in a smallish room, and they sound quite nice at low and mid-volume levels! I have a CJ PV-15 pre-amp feeding into a JWN tube amp, which has 8 el34 output tubes. Lance Cochrane estimate it at around 100 watts per channel. The amp itself has a higher sensitivity than my old solid state CJ AMP, and it controls the bass better as well. I get an incredible soundstage with lots of three dimensional detail. Something about the ribbon tweeters in the speakers makes them sound almost like panels in the mids and the highs, which are to die for.

I have the speakers around 7 feet apart, and I sit about 10 feet back.

Poor design. For if the loudspeaker is large but designed to integrate and work in smaller spaces it can. Its many of the smaller designs that are compromised and under sized for proper sound quality. And may require near-field use in small rooms due to extensive Thermo and dynamic compression. Most Subwoofer designs again are compromised in design and one ends up with a large excursion driver in overly small cabinets thus requiring massive power and floor or corner boundary reinforcement to produce lower frequencies. And again Thermo compression rears its head as large power is forced into voice coil. Reducing efficiency, dynamics, transients and adding distortion.

Good points Johnk. How many speaker manufacturers actually build big speakers designed to work well in small rooms?

Everybody seems to want the smallest form factor they can get away with. Unfortunately that leads to the problems you addressed.

It would be nice if manufactures would list what room dimensions are optimal for each model they make. Might make it easier for the consumer to figure out.

My guess would be woofers that create to much bass energy(air movement) and then sounds bloated.