HD 25-1 II are very true to the source. I mean they just show what is there, it's all so evident in your face, clear like day, emotions, impact, clarity, depth, neutrality. If the source is harsh, dull, dark and flat, or whatever HD 25-1 will sound like that, but if the source is exquisite, balanced HD 25-1 will sound so real you will be feeling right in front of the performer. So happened I gave my headphones to some of my friend audiophiles and they liked it so much they wanted to buy a pair as soon as possible, quite amazed they never heard of these before(thanks to sennheiser marketing I guess) and they just told me what I told you about their true to source character. These, in our opinion, are some one of the almost perfect monitoring headphones and yet so pleasant to listen to, it's a lot of fun.
Those of you who got them just now please brake them in for like 200-300 hours and then you will see what a treasure these are, they will open up and lose the harshness, or tightness in the upper part, you will be able to listen for hours and not want to take them out. HD 650 are not on par imo if you listen mostly to dynamic music and I mean not slow music like classic, or slow jazz. Just listen to a pair of HD 25-1 for some time and then switch to HD 650 and you will see what I am talking about. HD 25-1 to me is realistic sound in your face, so sweet, candy taste like sound, so spot on, while HD 650 is like sitting in a hall catching sound from air, quite boring, distant and thin, not so real true to life sounding. Sorry if I seem a bit unfair towards HD 650, I don't mean any disrespect, they're still the same brand, it's just that HD 25-1 are that good to me, and not only me as it was found out. Love and cherish them, these little pieces of discovery.