Spkr size vs. Room size

Where do you draw the line.Can a speaker be too large for a given video room?
Only if you can't fit anything else in the room ;-)

Seriously, I've had wonderful experiences with large speakers in fairly small rooms. One of my fondest memories is of a homemade JBL professional series speaker system (circa 1971) with very large horns for the midrange and tweeter and 15-18 inch woofers all housed in large cabinets in a room no bigger than 12 by 15. The sound was great. Usually, it's the bass that might be too "large" sounding with large speakers in a small room, but video systems tend to have one or two subwoofers so a large speaker system in a small room may simply remove the need for one or both of those. My two cents.
It is easy for speakers to overwelm a room. Small speakers are appropriate for a small room, medium for a medium sized room and large speakers for large rooms. There are no real hard, fast rules for what is a small/medium/large room, but the person in the room can tell. It is better to err on the small side with speakers. A small speaker can do okay in a large room but a big speaker moves a lot of air. If the room doesn't have enough air the speakers cannot perform as they were intended to perform.

A small room will reinforce the bass region in places where it does not need reinforcement. This occurs from two different sources. Since the room is small there is not enough room to pull the speakers out from the rear wall. This acts to diminish soundstage and amplify bass. Bass needs room to expand and develop in a room. The length of the room is what determines when, or if frequencies devolop fully. The deeper the bass, the more length required for it to bloom.

So yes the proportions between speakers and room are critical. It can oftten be seen here on AudiogoN or in letters to the editor in different rags that someone says HHKJHBTFHGKJ speaker company suck, since they heard these speakers somewhere and they sounded either congested, or bloated. This is an innacurate and unfair appraisal of what was heard. These characterizations are almost always room issues not speaker issues.

I don't know if this makes any sense, but I'm trying to say it as simply as possible. There are others here who might be able to answer this more aptly.
It just seems that the better I acoustically treat the room the smaller my speakers sound.I think it is voiced quite well with good decay times and it isn't overly absorbed.I followed a live end, dead end theory and happy with the results.Just wondering if after acoustically treating your room this has happened to you?
It depends how you define large.

Box speakers suffer/benefit from up to 12dB/octave of room gain once half a wavelength (1130 feet / frequency / 2) exceeds the longest dimension.

Put a box speaker with low bass extension in a small environment (like a car) and the bottom end will be very exagerated regardless of the physical speaker size.

All else equal a bigger box will get you lower bass - but ports change things. Just using larger drivers won't get you lower bass - although all else equal you'll get less distortion and lower off-axis response at higher frequencies. It's also possible to electronically correct the excessive bass with a shelving high-pass filter.

Full-range dipoles also don't experience the effect. You could run a dipole sub-bass system with 4-8 12-15" drivers a side and not have room gain.