Great review. I tried Sonarworks with a pair of Hifiman HE-400i and I found it improved the sound quite a bit. However, I felt like it boosted the bass a little too much and it added a subtle sort of “shouty” quality to the sound, which I believe lies somewhere in mid range between 1khz and 5khz.
I’ve since bought a MiniDSP EARS and MiniDSP HA-DSP, which by the way, I’m able to get even better sound with. With these, I have been able to significantly improve the sound quality of the following headphones: Audio Technica M50x, Hifiman HE-400i, and Focal Elex.
After measuring the 400i headphones with the EARS, the bass response I measured is quite close to most other measurements of out there (quite close to those SBAF, actually). Sonarworks measurements of these headphones show a very steep roll-off in the bass starting around 100hz, however, most other measurements, including mine, show a much narrower roll-off in this region. When I measure these headphones with the Sonarworks curve engaged, it shows a massive (~+12db above neutral) bump in the 40hz region. As a result of their measurements, I believe they have over-compensated in this area with these headphones. I wonder if those that they measured had worn out earn pads, which can apparently cause the bass to roll-off more steeply due to a flimsier fit. I found their bass measurements of the Audio Technica M50x and the Focal Clear Professional (closest they have to the Elex) seem closer to what I get with the EARS.
I cannot hear a difference between the filters.