I used ATC SCM 20 and a sub in a room with space for a complete badminton court, hot tub and large ornamental fig tree. Approx dimensions were 50 feet by 36 feet with 11 to 18 feet vaulted ceiling. No problem at all to fill this space (but I absolutely needed the sub) and I like to listen extremely loud - everything was wood with windows along two sides...not the best of acoustics due to the reflective gymn floor.
So if you get speakers with very wide and even dispersion that play at pro SPL levels with low distortion then they will fill any space well (won't fix reverberation issues but will fill the space evenly).
Without naming names (and upsetting owners), my experience with these small ATC bookshelf speakers compared to several other brands of consumer speakers (big well known names) caused me to radically change my opinion about non pro designs with non-pro drivers. Today I would not use anything but a pro design in a large space.
So if you get speakers with very wide and even dispersion that play at pro SPL levels with low distortion then they will fill any space well (won't fix reverberation issues but will fill the space evenly).
Without naming names (and upsetting owners), my experience with these small ATC bookshelf speakers compared to several other brands of consumer speakers (big well known names) caused me to radically change my opinion about non pro designs with non-pro drivers. Today I would not use anything but a pro design in a large space.