Iqlima, most humans can actually hear 20Hz, the only problem is not many speakers can reproduce that low note correctly. Most of the time, you will end up feeling the 20Hz moving air instead of hearing it. In my car, using my test CD, I can actually hear the 20Hz, but on my home hi-fi, I can only feel the moving air. If you are using a good pair of headphones to listen to the 20Hz, I think you should be able to hear it.
The "feeling" that you get when you hear a 20Hz note is actually very similar to the feeling you get when you are near a bunch of elephants... heck, elephants communicate using infra-sound frequencies anyway... 20Hz and below.
Or maybe it's just me being a bit weird to be able to hear so low.... hahaha...
LCP