Sorry, but the DT880s are open headphones too. While beyer calls them semi-open, they are open...like semi-pregnant I guess.
I prefer the DT880/600s by a small margin. The treble could be a little hot at times, but the tonal balance is more neutral than the HD650s (I was a former owner). Sound stage imaging wise they are both equal. I do give the nod to the Senns for the mids.
I prefer DT880/600 due to its more colourless/sterile, more refined (IMO) mids and transparent highs over the 'relatively' muddy mids and more congested and less transparent sound of HD650s. But one should note that mainly the genres you listen to shape your taste, what kind of a sound signature you are able to appreciate. I personally listen to classical music and jazz, and hate pop music which I believe HD650 fits perfectly with its fuller mid-range and more bass presence.
i have both and i prefer the dt880. i like the cleaner sound and tonal balance as per my ears. it can also provide a larger soundstage and the headphones are more comfortable over the hd650. the hd650 excels at reproducing vocals, something that the dt880 cannot touch. it's a personal preference, and is also influenced by the type of gear used to support the headphones. i guess my current setup favors the beyer sound
Previously known as Jack-Micca Member of the Trade: TekFX
May 20, 2010
I also have both and also prefer the DT880/600 to the HD650.
Warning: personal subjective opinion follows.
I tend to think that HD650 is one of the more over rated headphones. It just doesn't have much of anything going for it beyond being merely competent in terms of sound quality. It's probably the heaviest headphone in my collection, and the clamping force is much higher than necessary. The ear cups do fit completely over my ears, but are not as comfortable as the Beyer's. I would say these tie with the Ultrasone 650 Pro for being the least comfortable to wear headphones in my collection.
In terms of sound, the HD650s has neither the detail/transparency of the K70x nor an endearing playful sound signature like the DT880/DT990. So what you get is a pair of adequate headphones with a dark sound signature. They work well if I listen to them, definitely a good pair of headphones, but compare them against other fine headphones on the market I find myself preferring the sound from something else.
If I were to draw a parallel, I would say Sennheiser HD650 is the B&W of the headphone world: great reputation, awesome resale value, but you can do a lot better for same or less.