OFv2

[Shannon]

 

 or, if you absolutely must use earbuds and ultrasonic, then use the ocean surf track to set the volume to a comfortable level and then drop it by an additional notch and use that volume for US.

Would it matter if I cannot hear it (the US) at all?

The question is...

Is there ultrasonic audio being produced by the earbuds?  If so, then you're almost certainly going to damage your ears at those volumes using earbuds.  If not, then you're listening to silence.

The question of whether you can hear it or not only matters in that sense, because if your earbuds are producing ultrasonic audio, then you can hear it.  Even if your conscious mind is unaware of that fact.  That is, in fact, how and why ultrasonic subliminals work.

Fab10 brings up a good point also, and using earbuds at those volumes with ultrasonic should be producing horrible tinnitus.  That makes me think you may have accidentally been saved by crappy bluetooth compression stripping out the subliminal audio entirely.