Decided to post my own impressions about HD650. There is a lot of stuff said about these cans, the words that appear most frequently are "warm, mellow, smooth, laid-back".
While I certainly agree with these characterizations, I would like to add some description that, I think, is even more accurate.
First and foremost, the sound from HD650 is SOFT. During a drumbeat, it sounds like the drum has a thin cushion layer on it. In contrast, the sound from any Grado is shrill: when it hits my ear, it feels like a dentist drilling through my brain :)
This artificial softness of HD650 (yes, it is artificial, the original music in the studio will not sound like that) makes many people describe HD650 as veiled.
Second, the sound from HD650 is COLORFUL. Imagine two TV pictures: one has more brightness and the other has richer color. HD600/800, AKG, Grado all have a brighter picture; HD650 has a more coloful picture. My ears get sore from all the bright high frequencies in the other headphones, such music presentation does not deliver more detail, nor does it make listening experience particularly pleasant. I often have the impression that high frequencies carry significantly more variation and information in HD650 while in other headphones, they sound flat and harsh. I actually think it's an artefact of digital recording which HD650 magnificently correct.
But the most apt description of the HD650 sound came from my father. When he listened to them, he said that their sound is DAMP. Just like when a person coughs, his cough can be dry or with some moisture (called "productive cough", I think). HD650 adds this dampness to the sound making it very pleasant to my ear. In contrast, Grados deliver very dry sound and HD600 are not as dry but much drier that HD650. If you like your crackers with milk or tea, you should enjoy HD650 sound signature. My father did not like the dampness.
To sum up, HD650 are very unusual headphones. They make alterations to the music that are too obvious to call them "high-fidelity". But I realized that fidelity or accuracy does not equal enjoyment. This is especially true with low quality recordings. HD650 makes them sing and puts soul into them, something that no other equipment - phones or speakers - does. To me, HD650 are a masterpiece of engineering.
P.S. Actually, may be someone here can recommend a speaker system with similar sound qualities as HD650? I've been looking for smth like that for ages. Thank you!
Edited by musicismagic - 1/15/13 at 5:34am