0_0 DT990s are flate plate measurements proof. (EQed Apex220 measurement mic) All graphs are compensated to their respective HATS diffuse field. Graphs are normalized at 200 Hz

Red : Resolve ; Blue : Auriculares Argentina KB50XX ; Yellow : RTINGS 5128c ; Cyan : Oratory1990

Flat plate vs Oratory (probably multiple samples average)

I wished it was not the case, but the flat plate measurement, especially being so close to the Oratory1990 one, prooves that flat plates measurements for this headphone are valide enough.

The standard deviation of all KB50XX measurements is very big leading to big unit to unit variation and measurement procedure deviations. The flat part at 8 kHz on Oratory's measurements shows a big standard deviation there. If it's an average of multiple units. By knowing Oratory's excellent measurement procedure, the flat plate agrees mostly with his potential average of multiple samples. Even after 10 kHz.

The lack of more 5128c measurements of this headphone bring some uncertainties about frequencies above 10kHz. And even with all compensated measurements.

The convergence between Oratory's measurements and mine is peculiar though. I'm thinking that the GRAS rigs with KB50XX pinnas, and their variants with the same ear canal entrence shape, are the most accurate one. Although it's not that a flat plate measurement meets these rigs that it asserts they are accurate.

So I'll use the EQ I did with my flat plate measurement. If you want to measure your own unit using a cardboard box and one or two EQed measurement mics, you can do it if you want. It will always be better than nothing. In this regard you will be less forced to relly on averages or to another unit and measurement procedures that will be fundamentally differents. You will lose nothing as it always will meet the standard deviation I showed in this humble short meta-analysis. And even IEC711 and KB50XX clones may have unit to unit variations and every mounts of these clones may not have the same interpinna distances. With all the DT990s variants, you will get something closer to neutrality.

To conclude be always cautious with flat plate measurements. My test is just one drop in the ocean currently. I got bad results with my Superlux HD681 and HATS measurements were more accurate. (RIP to this headphone)