I've pointed this out a few times when this graph has been posted, so sorry to repeat myself again, but it should be clarified (since Axiom kind of glosses over this point) that the average spectrum of music is far from flat.
So when Axiom says that the music was playing at, say, 86dB, that certainly doesn't mean that the level of the music was 86dB in the treble.
In fact, typical spectra of music look something like
this:
View attachment 97861
Which interestingly is a very similar shape to the threshold curve that Axiom generated from their tests.