Very interesting. Thank you.
Does it affect some people more than others?
Am I understanding you correctly that maybe if I EQ each ear separately and played around with higher frequencies with some filters, I might be able to find and attenuate the frequencies that cause the trouble for me?
We can perceive an audio "phantom center" when our listening position relative to speakers is just so. We can perceive where musicians are located on "stage" relative to one another when listening to headphones. Yet with IEMs we get a different perception that either of those circumstances; in part because the facing outward ear pinna is not involved.
The phrase "pinna gain" is probably assumed by most to be a uniform sound frequency pressure wave that propagates inside the ear canal equally in all of that space leading to the ear drum. What I alluded to is that inside the chamber of the ear canal that "gain" does not exhibit equal strength in all vectors, and more significantly at every different HZ frequency at the same dB the pressure pattern inside the ear canal can be variable.
I will below post 2 diagrams, one for 9 kHz frequency and the other for 12 kHz, for how (in that example) 10 dB gain showed up one man's ear. You can see how they also have different sectors of break up in certain "lobes". We can not say that every human ear will exhibit the exact same pattern, but let's take it as an example of the potential for different "lobes" of sound pressure presenting at out ear drums. Bear in mind the diagram is only 2 dimensional and the ear canal chamber is 3 dimensional.
OK. So with sound wave directivity from the pinna (& diffraction from the within the head) we get a notable dB gain at the upper outward face of the ear drum with a treble frequency. And human evolution has programmed us for responding to this quickly inside our brain - we needed to be done with processing some chirping bird up above our head so we can be alert for sound of any predator.
That upper face of the ear drum gain gets signal transmission connectivity into what we are evolutionary driven to create inside the brain as a template for treble processing. With IEMs in we don't get the pinna gain paradigm, but we still retain in our brain some kind of signal template inside the brain for treble frequency patterns. However the installed IEM, by blocking the ear canal, creates a different pressure diffusion on the ear drum - presumably more uniform at more frequencies than lobed.
I posit that with IEM there is less "lobe" of pressure (focused gain) reaching the ear drum that itself still has some inter-relation with our pre-existing treble recognition template for pinna gain. My surmise is that this causes some pattern mis-match with the involved brain neural network we naturally develop from evolving with pinna gain. Kind of like the brain is not executing a completely natural (pinna treble gain) signal transmission, so expends more neuro-chemicals in a futile cycle and over time some connectivity to brain cortex is reduced leading to treble fatigue.
Addressing your questions: I do not think tweaking IEM input controls automatically will always resolve the issue. Certainly there is going to be variability among individuals and one's 2 ears. My surmise is the issue is not a frequency, per se (ex: treble), nor merely listening volume. My opinion is that as adults we've laid down inner brain neural pathways that are matched like templates to process the different high frequency pressure lobes of gain in our unblocked ear canal. The sound controls to modulate an IEM's output can not annual those brain connections - our connection patterns laid down seem to keep doing something.
Unedited, pardon any poor presentation.
