I start hearing it at 17.5khz.
DT 990 Pro. Interesting that I hear about the same on my $300 desktop monitors, I thought I'd lose at least 500hz on the monitors for some reason.
Explains why I'm not very good at hearing the 20khz cut I put on my 2-bus
BTW, here's another version of the test:
youtu.be/VxcbppCX6Rk