Its generally counted in merit if a headphone has a spacious sound. If it sounds closed in or restricted most people don't like it.
Sound signature is even more subjective. I also find the hd650 sound signature to be my preference over the Alpha Dog, and def the yamahas( no way they are better than the hd650 sound signature or not. A well amped hd650 is not to be mentioned in the same sentence) The Alpha Dog is the better headphone in merit and sound quality to the Mad dogs but I like the mad dogs sound signature better. I like warm and rich sounds over lean and bright ones. I prefer a little color over neutrality because it sounds more natural to my ears that way. I am 33 so my ears are still a bit sensitive to treble and tolerant of bass.
I listen to jazz, hip hop, electronic experimental instrumentals, contemporary christian worship music, dub step, reggae, and post rock.
I have no measurements.
The hrm-7 vs he400S after comparisons and having them both here as I type.
tighter bass: hrm-7
easier detail perception: hrm-7
deeper bass: hrm-7
bigger sounstage: hrm-7
better midrange tonality: 400S
better voc 400S
treble extension: hrm-7
liquidity: 400S
Openness (less reflectials
n or reverberations from cups): 400S
Clarity: can go either way depending on the song. 400S gets the edge.
better imaging & instrument separation: hrm-7
You can interpret that for the hrm-7 or against the 400S. Take your pick. Either the 400S doesn't behave like you would expect from an open back planar or HRM-7 is a bit unique compared to what I have had the chance to audition/buy.
To understand how I look at things, the he-4 (sounded hecks more open than the X and airy as well, just as fast too) embarrassed the Audeze LCD-X on songs even though the Audeze is better. Just not 1100 better or even 300 dollars better and based on what you would expect. Certain headphones make you raise your eyebrows very high when you compare them directly. The Hrm-7 would not be expected to have tighter bass, better instrument separation, or bass extension than an open back planar.