I'm no expert but my understanding from when I was in the Army is that high frequencies are much more damaging than low. This became a problem when the forces adopted higher velocity weapons which produced a much higher frequency pulse of sound when the bullet leaves the muzzle.
I believe what happens is the bones of the inner ear get damaged by the vibration where they meet. I'm not aware of any significant problem with hearing damage from leisure aviation in normal SEP. ANR is more to do with reducing fatigue and increasing intelligibility IMHO.