Hi GregM,
Paired with a good sub, and conditional on your listening-taste, I'd say about 2,500 cu. ft. The M22s will play cleanly at remarkably loud levels running with a good-sized subwoofer in 5.1 channels. I've measured peak levels in my listening area of 100 dB SPL. That's perhaps 2 dB louder than the peaks I'd normally measure playing back big orchestral works with bass drum, pipe organ and chorus.
Last night I attended a solo piano recital by Angela Brownridge in a small recital hall. Seats about 400 people and has excellent acoustics. She played a giant Steinway concert grand. I sat in the 4th row, about 30 feet back from the piano.
I was surprised by the peak levels I measured on the ol' Rat Shack SPL meter. During some Chopin and Beethoven works, particularly the Beethoven Sonata in F minor, Op. 57 "Apassionata," the meter peaked over 100 dB SPL. It was certainly loud, but in the larger space of the recital hall, it never seemed "too loud".
Regards,
