Smallest room dimensions for good bass to 20hz

20 HZ is 56.6 feet long, so I guess the perfect room would be that long or longer. I doubt there are many homes with a stereo room that length, so maybe all of us are compromised?

Maybe Rives or some other acoustics persons has a formula that determine how much less than that still works fine for our needs.

Is there a formula for figuring out how long (in footage) a given frequency is?
I thought a frequency of 20 hertz would be a wave 20 feet long between peaks.

So what does it mean if your SPL gets a good rolled off read when you play that frequency?

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

I get a compensated/corrected reading of 21Hz at -3dB in my 14x13 room at the listening position. That works just fine for me.

Arthur