Nonsense! Find a person who can hear a 20,000-cycle tone and can afford the electronics necessary to reproduce it. Then find another. I would guess that finding two in the same week would be difficult.
Perfection is the enemy of good enough.
Tell me about it. When I was around 20 I had to have a TV repaired because something came loose and the flyback transformer was howling at its 15.734 kHz frequency. The old repairman couldn't hear it even though I could barely stand to be in the same room with it. I doubt I could hear it anymore.