I can only hear the 8k sound. 

Found this one too. With PC speakers I can hear about 13,125.

I was about the same as you Snowy but Mrs Data could hear up to 16,000.

Pardon?

After a couple of decades of abusing my ears in a shop environment without using protection of any sort, I have a constant "ringing" (I think of it as more of a whistle) that runs around 13kHz 24/7, so it's no surprise to me that I don't hear anything on those tests above that frequency. In the test, I begin to hear a "crackling" noise that's very faint @~15.7KHz, but it doesn't resolve into "sound" till ~12.4KHz