Why do people still post drivel like this?
Deep bass frequencies in recorded music are between 40 and 50 Hz. The lowest note in a rock band is 42.5 Hz
This is wrong on so many levels, it's hard to know where to begin. But even if a note is played at 42.5hz, in an enclosed space there will be harmonics snd room effects providing location, scale snd depth far below that level.
An excellent way to demo a high quality sub is with recordings of human voices in a large space. A church, for example. Listen first without the subs, then again with the subs. The subs will reveal the space the vocalist sings from and the audience being sung to. So it is immediately apparent that even human voices benefit from sub 30hz capability.
Then we get into different genres of music. If you are willing to have a system that censors anything below 40hz that is your choice. But personally i enjoy modern music which often has real power below 40hz, or the 'fear factor' as it is widely recognised. Genres like deep house, trip hop, drum and bass and hip hop benefit from a system that retains real power down as low as 16hz. If you only listen to music from the previous millennia you may make a judgement that this zone is not important to you. But to deny that it exists is nuts.