A Bass Question

A 20 Hz wavelenth according to this webside http://www.mcsquared.com/wavelength.htm is 56.5' so I am not sure how you arrived at 27.5'. My own room measures only 13' and I have speakers which go down to 33Hz and a sub which goes down to 10 Hz (-3db) and I can assure you I hear well below the 90hz (12.5') wavelength that the room can accomodate.

My sub only switches on when there are signals below 33Hz and as such I can say for certain music (light jazz) its always on while for some (classical) its off except for brief moments, so depends it really depends on the music.

My understanding is that we hear based on vibrations the ear drum picks up and not on wavelength. We can hear in water too or by placing our ears on any medium that will transmit sound like a wall. Take earphones which operates by moving the air in the ear cannel coupled to the ear drum.

The only reason for a large room is that you reduce reflections as a result of being too close to walls. So I don't really see why you would need a huge room to accomodate a 20 Hz wave. Can someone explain this?

My room is similar in size to Athipaul's and my sub also only switches on when bass signal is present. Although with mine once it's on it rarely goes off while music is present; it has a ten minute minimum. I feel like I'm hearing good clean bass in this small, well-treated room.
It was all done through experimentation as I initially ran the system with zero treatment for a few days before purchasing the treatment material. The sound was all over the place and bass notes were boomy or nonexistent depending on where I stood/sat. Now the bass is clean and even anywhere in the room.
How low does my system go? Can't say exactly as I don't have any measuring device, but tracks I use when auditioning equipment for bass reproduction are working very well. I suppose you could go the scientific route; get out your calculator and measuring tape but your ears will make the final judgment.
I would think with a room your size, getting solid, even bass distribution would require even more work and a quality sub or two. Good luck.

The fundamental of the E string on a bass guitar is 41.2 Hz

Even though the full 20 Hz wave will not be found in your room, you will get an air pressure wave at 20 Hz.