What are "Full range speaker"

S23chang, where did you get that figure from? Sources I know of say 20hz is the human low range limit.

My speakers do -1+1db sub 20hz to beyond 20khz. But then, they are three way.

Yes, we're physically capable of 20 to 20k yet we don't hear the extremes often unless you have your system is hooked up to a frequency generator.
I'm not sure what note you can hear at 20 hz but I only felt the "wind".

Happy listening

I can't think of anything that generates a 20Hz note. However, there are plenty of natural phenomena that generate sounds incorporating 20Hz frequency in part. For that matter, much lower frequencies too.

I can't think of anything that generates a 20Hz note

A church organ, for one. Chips... (OK, that's an electronic device).
One problem with actually "hearing" a 20Hz note is its length -- ~17,5 m. So, when it's there (rarely) we perceive reflected sound.
It's also very difficult to reproduce, requiring tons of amplification power and excursion from the driver(s)