20hz is the area that subs should reproduce at loud levels without distortion. Under that and you've got a world class sub. Once you've heard ultra low bass cleanly you won't go back to lesser subs. Some movie soundtracks go down to single figures, I'd say 10-15hz is ultra low bass. Once you go down to single figures then you've got something stellar. Music doesn't have low bass, except for synth.
I don't think you've actually felt a real sub, you keep on using the word "hear" But that's not suprising if you've only heard headphone bass.
it has nothing to do with music, all your statements about your incredible headphones that can get down to 2 hz are ridiculous.