I recently swapped out my sub amp., going from an older class AB 150 watts/channel to a modern class D 600 watts/channel crossed at 100hz. Aside from the increase in output and low end extension there is a very discernible increase in mid-bass, lower midrange tonal accuracy, intelligibility, depth, impact and sound staging, in fact the improvement in sound staging is rather amazing.
Now I get how the mid-bass might improve but the effect on instruments like congas, toms, sax, some woodwinds and mid-lower register instruments in general is noticeable. Of course some of these instruments are capable of lower octave reach but the improvement reaches well above the lower octaves.
Anyone care to comment on what's going on?