What I would like to know: Has anyone actually done frequency response measurements of their headphones or IEMs and used the dual independent EQ to match left and right side?
Sort of. I'm using my ears as the test rig to create a perceived FR chart.
I have mild hearing loss of higher frequencies in my left ear.
I use EqualizerAPO and Peace to determine threshold of hearing data. I translate this to normal listening volume using equal loudness data. And then there are some adjustments I make based on past results.
I can then feed this data into AutoEQ along with a target influenced by Harman. It's not exactly Harman because that's for a specific test rig, but the ideas to compensate for various types of ear gain at different frequencues are similar.
My EQ settings are generally the same under 500 Hz and reach their peak differences at about 8000 Hz.
The end result is that my ears perceive near equal loudness through the frequency range. There's about a 25 dB difference when uncorrected at 8 kHz. This shows up both in my data and the audiogram from my audiologist. This generally corresponds to roughly half that at normal listening volumes. Simplified, I cut the right by about 6 dB and add about 6 dB to the left, and it gets really close. I'm adjusting the "FR chart" data I get and then letting AutoEQ generate the settings, and I've had great success with that approach.
Music sounds centered to me after applying the custom PEQ by channel. I'm using "I" above, but these aren't all my original ideas. I've learned a lot from someone else already doing this.