Greetings to everyone!
So I've been using the R70X for a while now and find them to be a very good pair of cans for the money.
Imaging is spot on, extracts tons of details, doesn't sound congested and offers good seperation and soundstage, very nicely textured bass and good sub-bass presence. However the best part is the comfort which is probably the most underrated quality of this headphone.
The thing I did not like is the overly long and poor quality cable. The earcups fit my ears fine but they might be small for some people (or if you're a troll).
In direct comparison to the HD650, these are slightly more "flatter" sounding with non-accentuated mids unlike the 650. Switching between the two, I prefer the R70X for its clear, unveiled sound with better bass than the 650 along with the better comfort.
I would also like to note that most reviewers/users everywhere seem to present contrasting opinions on the type of amplification for these headphones. I found these to be fairly difficult to drive from portable sources and they really came into their own using desktop amplification.
These are relatively analytical when used with solid state amps and they really shine with tubes providing good sub bass and very engaging midrange. The tube amp I'm using allows for impedance matching and I found that doing so provides very good result with the amp having a solid grip on the transducers and really making them sing.
All in all, YMMV with the amplification but in the end, no matter what amp you use, if you're using a dedicated desktop amp you'll surely be satisfied.
These are a perfectly good stopping point for any midfi setup and a benchmark for resolution and neutrality in the sub 500usd price point.