Great to see Sennheiser trying out some new studio designs. This market needs more competition. And this headphone looks like it has a some potential, but also maybe a couple areas where it could potentially use a few tweaks or some work, from my perspective.
The headphone has plugs on both sides, for example. But it looks like the cables are single-sided, which I'm not a fan of. (Maybe there's a way to use a two-sided cable with these though?) Aside from that, the ergonomics and build look pretty decent, and like somethin I'd probably enjoy using.
Based on DMS's measurements (done on his HBK 4128 rig), the response appears to be fairly neutral-ish, but with some slight possible caveats. I'm lookin primarily at the raw graphs at around 3:50 in the above video...
Bass extension looks pretty good for an open dynamic headphone, with the velour pads. And the transition into the mids looks smooth. (This is more of a problem on alot of closed studio headphones I've used.)
Mids look pretty good, except perhaps for the recession around 2 kHz that DMS noted. I prefer upper mids that are a little withdrawn right around 2k with alot of music I listen to. But this might be a bit too much for some. You can definitely hear the difference, and how that area begins to sound more recessed (or possibly even a bit muffled) on the HD 490 Pro vs the HD 600 video that drummerman1 posted here...
...The HD 600 is probably a little too forward for my taste though in the upper mids. (Your mileage may of course vary on all this.)
Re treble, on the 4128 rig, I generally like to see a pretty nice, well-defined peak at around 3k on the raw measurements, give or take. And then a bit of a dip between that and the next ear canal resonance at 9 kHz. What I'm seein on the HD 490 Pro though is a peak at 4k, and another small one at 6.5k. So this might come across a tad bright or sibilant in the low to mid treble. It doesn't look too pronounced though, based on these preliminary plots. I'm pretty sure this headphone will also end up on Resolve's 5128 rig though, at some point, which may help to clarify things in this area a bit more.
The high treble also looks a bit rolled off. So maybe lacking a bit of air near the very top of the audible frequency range. This is something you'll see on other studio gear, including the AKG K371, Sony MDR-7506, and Senn HD 280 Pro, to name a few. And I believe it's ostensibly done to reduce ear fatigue. I'm not sure it's a good thing though from a music listening standpoint.
This is all conjectural though until I can get a pair to try myself. Or can see more graphs.