"Unfortunately I don't think it's possible to globally EQ these because they are very inconsistent unit to unit."
With the PR2 v2's frequency response now being controlled entirely by electronics and a nozzle filter, unit variation will be reduced to an absolute minimum. PR2 v1 would exhibit more unit variation because of the greater potential of misalignment of the filter over the driver. This greater potential was due more room for filter movement leading to a loser tolerance.
It's not possible to create a universal EQ, which is something that even Harman doesn't attempt to do, because of Head Related Transfer Function and personal preferences.
Here's an example of the shelving filters used in Harman's research:
These are variances on the order of ±10 dB!
Dr. Olive, one of the principle researchers of the Harman targets, can be found discussing it himself
here.
Regarding HRTF, it is "a response that characterizes how an ear receives a sound from a point in space. As sound strikes the listener, the size and shape of the head, ears, ear canal, density of the head, size and shape of nasal and oral cavities, all transform the sound and affect how it is perceived, boosting some frequencies and attenuating others. Generally speaking, the HRTF boosts frequencies from 2–5 kHz with a primary resonance of +17 dB at 2,700 Hz. But the response curve is more complex than a single bump, affects a broad frequency spectrum, and varies significantly from person to person." -
Wikipedia - Head Related Transfer Function
When both unit variation and especially HRTF are taken into account, the futility of attempting to create a universal EQ profile for the PR2 becomes glaringly obvious.
So, we start with a baseline, which is whatever target response curve one generally finds to be the most pleasing - with the PR2 this was what the collaboration between KZ and HBB came up with - and we personalize it from there.
