If your being moved (physical displacement) to the music from the acoustical pressure wave forces below 20hz. that you can not hear -- not my kind of dancing.
So you are right on .. keep the SW's above 20 Sec.^-1.
Move your Rythmik to 20 Sec.^-1 and put the rest of that Energy that you are wasting below 20 into the Human Audible BandPass Spectrum, why waste it moving the walls?
Or maybe you just like watching the walls Dance, instead of the Private Dancers.