Frequencies >20kHz?

Hello everyone,

I hope this is the right category to ask about this. 
I'm always curious about the speakers with frequency ranges above 20kHz, highest frequency audible for human ears. I quickly googled it and found some research papers claiming that ultrasound frequencies still make a difference for the listening experience (like helping the perception of sound quality).  

I personally don't really feel the difference to be completely honest... can someone please share their experience?