8f - high
15f,2" X 11f,2"
However, large room with good dimentions will always sound better then small room with good dimentions becouse: larger the space - more resonance modes which are more closly spaced in frecuency and will have smoother distribiution.
M.S
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The best-sounding non-large listening rooms should have a length which is 140-230% (139-233% exactly) of their height (which for most of us can be normalized at 8' ±, more precisely 7.5'-9'), and their width should be within 5% (±5%, that is, or 93-110% exactly) of the geo-metric mean of length and height. The venerable 1:1.26:1.6 ratio
For an 8' ceiling, then, ideal length ranges from 11.1'to 18.6' (say 11-19') and width, provided it meets the geometric-mean (which I now dub least-cubes") restriction, from 8.8'to 12.8' (say 9-13').Within these limits, the larger the properly proportioned room, naturally, themore pleasing also its reverberation time below 500Hz-1kHz.
The Boston Audio Society - Vol. 17, Num. 6 May 1990