Where hearing ends and feeling begins
20 Hz is the conventional floor of the audible range, but the boundary is soft: at this frequency the sensation of pitch largely disappears, and what remains is felt as a flutter or pressure - in the chest as much as the ears. Play it loud enough and anyone perceives it; the question is whether it registers as a tone. Below 20 Hz lies infrasound, which is perceived (when at all) as vibration and unease rather than sound.
Equal-loudness curves are brutal down here: to sound as loud as a comfortable 1 kHz tone, 20 Hz needs roughly a thousand times more acoustic power. That is why the deepest octave is the most expensive one in any speaker system - and why most gear simply does not attempt it.
What can actually play 20 Hz
Almost nothing in a typical home. Laptop speakers give up around 150-200 Hz, bookshelf speakers around 50-60 Hz, and most budget subwoofers roll off by 30-35 Hz. Genuine, clean 20 Hz output takes a serious sealed or ported subwoofer, big drivers, and real amplifier power - or good over-ear headphones, which reach it quietly but audibly because they only need to pressurize the tiny volume at your eardrum.
What you hear through small speakers on this page is almost certainly harmonic distortion at 40 and 60 Hz, not the fundamental. The honest check: step down through the subwoofer test one hertz at a time and note where output truly dies, or sweep the whole bass region on the bass test.