I've had Sennheiser's HD 700 for the past few days as a review unit, and I'm slowly putting my thoughts together on their sound.
I'll admit that I'm having a harder time than usual getting my thoughts cohesively on paper for these, and I'm thankful that I'll have them for a while so that I can be more decisive.
I really love the design of these headphones, and it's clear that Sennheiser was aiming for a relation to the HD 800, which I think makes sense. I'll have a picture that demonstrates this in the full review, but I found it particularly interesting that once the pads and cloth coverings are removed, these headphones are just drivers and stainless mesh. As a result, they leak like nothing else. Sure, it's expected that open-back headphones will leak, but these just spray music out of their backs. Not a bad thing for at-home listening, but if you're in a dorm with a roommate and it's late at night, best to leave these on the hook.
Now to sound. Thus far, I've been really impressed with and mainly struck by their musicality. The conjunction of their openness with the driver's implementation yield great imagine and separation, with a wide, deep soundstage. Where other headphones might lose parts of tracks in the sea of instrumentation, these seem to have no trouble rendering out each instrument with grace and ease. They lean on the bright side, from what I've heard so far, but not abrasively so. There have been a couple instances where I've experienced sibilance and a little bit of sharpness, but generally speaking, the bass seems to tame the exuberance of the highs.
The bass extends well and has good presence. I'd still say that these lean toward the upper-end of the frequency response curve, though. However, on tracks where the bass is intended to be emphasized, these headphones present it as such.
The mids are well defined, if they lie slightly behind the treble. There were a few select tracks (see: Ripe's Down With the Darkside) where I heard what is commonly called the "Sennheiser Veil" in that the vocals sounded a little bit glossed over and almost stepped back, but that hasn't been a common experience.
These headphones were provided to me for review by Sennheiser. I am not being paid by anyone to write this review, to endorse the product reviewed, or for the content that I put in the review.
These headphones were powered by an Astell&Kern AK Junior, a Google Pixel, a Neurochrome HP-1 (with signal from a JDS Labs OL DAC), and by whatever soundcard is in the motherboard of my computer.
I have had these headphones for about a week and a half, and I have put about 15 hours of analytical listening time through them during that period.