The default targets are the best guesses for neutral. That's the best for mixing too. I've decided not to add reviewer targets as they have little evidence for why they would be good and AutoEq has extensive options for the user to tweak the sound to their individual liking.
It's a diffuse field response of the BK 5128 rig with a 1 dB per octave downward (dark/warm) tilt. There's no similar published research for 5128 as there is for GRAS rigs (Harman target) and this one is the best guess at the moment for the most neutral target for 5128.
Based on your expertise, do you think that this would work as an alternative for headphones not yet measured using the 5128?
1- You would get several measurements done using the 5128 gear
2- You would offset some GRAS measurements for the same headphones to the 5128 ones, and then get a delta function by that
3- Theoretically, this would give you the average difference between a GRAS and a 5128 measurement, and then you could "predict" the frequency response of other headphones measured using the 5128
4- Then, you could add this difference to any GRAS measurement and EQ any headphone to the 5128 Diffuse Field target
This could be a solution to not yet measured headphones using this gear. My IEMs, which were measured using the 5128, for example, definitely sound better when EQ'd to that. I wish I could hear how my over ears sound as well
PS: If I understood it right, the already existing 5128 Delta target on autoeq.app is supposed to mimic how the Harman target would sound to 5128 measurements. It's not what I supposed here. Please correct me if I'm wrong