20Hz and 20KHz are just general guidelines for where sensitivity rapidly falls to zero in people with normal hearing. A lot of (primarily young) people can hear frequencies outside that range. I can still hear a sine wave down to about 14Hz, and I'm not sure if the limit is from my ears or the audio interface that's only rated down to 20Hz.

I can imagine "feeling" 1Hz from a big subwoofer, but it's hard to imagine what actually hearing 1Hz would be like. I wouldn't rule it out, though.