Just thought I'd say some years ago I upgraded my HD650 to an HD800, and I'm once again back to the HD650 (plus some nice speakers for my "main" setup). In retrospect, I've tried far more headphones than I thought I would, getting into head-fi (the meme "Welcome to head-fi. Sorry about your wallet." is certainly correct
)
Sennheiser HD 800
Sennheiser HD 650
Audio Technica AD2000
Shure SRH-940
Beyerdynamic DT880
Sennheiser HD 280 Pro
Ultrasone Pro 900
Sony XB 700
AKG K500
Koss Portapro
I'm back to the HD650 and honestly I think it's safe to say these will be my headphones for the foreseeable future
. Why?
There's always been something about the HD650 that is very hard to describe that just makes everything sound so smooth, musical, inviting, and just overall nice and enjoyable sounding, no matter what I'm listening to. They're still the most comfortable overall (I found HD800s to be very comfortable but the extra weight is subtly less comfortable over time).
Just so I'm not misleading: I should say that there is no doubt whatsoever that my old HD800 is technically superior all around (except for just one thing: the HD800 doesn't seem to be capable of the warm and smooth/lush bass the HD650 does well by default, even with equalization - though maybe tubes help here for the HD800, I haven't tried them). When I find a recording that agrees well with the HD800 (e.g. a really good classical piece), it's absolutely unmatched how realistic and lifelike it sounds. However I found myself restricting the types of music I listen to on the HD800 quite a bit, because it's really too revealing. If the HD800 had the sound signature of the HD650 with the HD800 technical proficiency, and the lighter weight of the HD650, it would be the perfect headphone, but I don't think any such thing exists.
For me, I think the HD650 reaches an amazingly good balance in its sound signature that just makes every type of sound and music work, and it's certainly holds up well in terms of true detail and resolution in a very subtle/refined way, because it doesn't throw it in your face like trebly headphones. I guess I'm at a point where the HD650's very precise but refined detail is more than sufficient quality for me.
All I know is given the wide range of music I like to listen to, the HD650 is the only headphone I can always consistently rely on sounding amazing.