But calling it the flattest headphone available is a very big claim, and an unsubstantiated one, at that.
I feel the claim is very well substantiated.
In my experience, of trying several hundred of the most popular headphones we frequently discuss here on HeadFi, I would, without question, include the Sony MDR-V6 in a list of extremely neutral headphones with very flat frequency responses:
And this "flat frequency response" doesn't necessarily correspond with the graphs. This is from personal experience. Over time I've learned this. Sometimes the lesson was expensive lol.
As for what i term "flat".......
The most important part of the spectrum to get flat or natural, to me and other pro audio guys, are the range from 40hz to 3kHz. Especially from 150hz to 2kHz. How flat a headphone is below 40z doesn't matter anywhere near as much as the instrument and vocal range to me. I mix and produce hip hop, neo soul, reggae, and rock songs often, including some big radio stuff. As well as remastering work for western music from the 30's to 70's. Maybe those who listen to dubstep or EDM want some practically inaudible 10z frequency to be as prominent as a 60hz, and are willing to trade frequency response above 1kHz to do it. But I am not.
This is why I feel Planar magnetic, when used alone, is an inferior technology in the headphone world, for professional applications. Ruler flat bass response in the nearly inaudible sub-30z range is a nice ancillary feature, but to me it is in no way an acceptable trade off for quite veiled treble and upper mids. In no way would ruler flat sub-30z bass presence EVER coax me to buy a headphone, over one with a far more deliciously natural midrange or treble extension, which showcased all the audible, MUSICAL nuance in the vocal & instrument range of the spectrum.
Hence why I personally favor these headphones above all others:
Beyerdynamic T-90
Sony MDR-V6 (I don't experience as much sub-bass roll-off as the graph indicates)
And have a very high opinion of these:
Beyerdynamic DT880
Shure 1840
Stax SR-009
AKG K601
AKG Q701 with bass port mod
AKG K701 with bass port mod
AKG K702
Audeze comes close with the LCD-X & LCD-2, but that veiled treble is still slightly present on them. Sennheiser and AKG come very close to perfection with the HD800 & K812, but both have slightly recessed mids to me, compared to the phones I list as the most neutral. I think the Successors to the HD800 & K812 will remedy this remaining issue and several other small issues with those two technologically incredible headphones. It's a shame the K812 has such an incredible design, nearly perfect bass response and quantity, and good, albeit somewhat too perfectly notched treble, for a "bright audiophile phone", but still, IMHO, is slightly recessed from 1k-5k, which makes them sound just as unnatural thru those frequencies as the HD800.