I have Beyerdynamic DT660 and AudioTechnica ATH-M50 at home for direct comparison if anyone is interested.
Beyerdynamic DT660 Premium
Price in Sweden: 130 Euros (200 USD)
Audio Technica ATH-M50
Price in Sweden: 130 Euros (200 USD)
Build quality:
Both headphones have very good build quality. They are very sturdy and seem to be able to survive lots of maltreatment. ATH-M50 is probably more appropriate for portable use due to its smaller size and the nice coiled cable. The ear pads on DT660 are to me just a little bit more comfortable and the headphone as a whole feels more comfortable, with smoother headband adjustments and nice pad underneath the headband softly touching my skull. ATH-M50 is not bad at all actually. The pads are made in some kind of fake leather that feels nice on the ears.
Isolation:
DT660 isolates a lot better, both out and in. No contest here.
Sound quality:
Both headphones have been "burned in" for 70-80 hurs. I used MAtrix M-Stage and Musical Fidelity X-Can amps with my Marantz 6004 CD-player. I also used my (international) Samsung Galaxy S3 cell phone. The ATH-M50 is the white box version.
DT660 sounds beautifully rich with acoustic music, symphonic orchestras, chamber orchestras, jazz. The soundstage is wide and quite deep as well. The midrange is smooth and nicely open, which is great for vocals. Depending on the recording the midrange can be a little strident and too forward. But the strings and brass in a symphony orchestra sound so natural and true. DT660 is not a bassy headphone at all and the lack of weight is easily noticed in some heavier electric music. With some songs from Green Day's American Idiot the sound is a little thin and congested. DT660 is not the first choice for heavy music even if it actually mostly handles it quite gracefully. Solo instruments like cello or guitar sound quite amazing for a headphone costing 130 Euro. (I mean, a headband for Sennheiser HD650 costs 110 Euro. That's a joke). With DT660 you actually don't have the feeling of listening to a closed back headphone.
ATH-M50 is a really nice sounding headphone indeed. The sound is somewhat recessed in the mids (compared to the DT660) but anyway quite open and clear with nice bass response. The soundstage is smaller than DT660. No doubt. The feeling of a closed-back headphone is there but not att all in the same way as with other closed back headphones I've head (excluding DT660). M50 sounds quite good with classical music. The midrange is nice and fluid. The strings have a nice bite to them and there is a good weight to the timpani and double basses. They're not in the same league with classical as DT660 but anyway good and I would say, quite possible to live with, With heavier music, they are a little better than the Beyers. The bass is tight and full sounding which gives nice weight to the sound. DT660s expansive soundstage works better on imaging and gives better air between the instruments. M50 has very "sweet" and easy to live with sound.
Conclusion:
I have never auditioned cheaper headphones like these before. My first headphone was Senn HD414 which cost me 40 Euros almost 20 years ago. I never compared them to any other headphone until I bought my HD650. After buying HD650 I only listened to headphones in the same price range or more expensive. I didn't have high expectations about headphones costing only third of the price compared to my Senns. After hearing DT660 and ATH-M50 I must say that I am really positively surprised. Although they maybe do not have the same "resolution" as my k701 or HD650 I actually think that they are not so far from them. DT660 is better than HD650 with classical. My AKG k501 with k701 pads is still my favorite here because of their beautiful midrange and fluidity. DT660 is not far behind. M50 is a great all-around headphone. It is not perfect with anything but still sufficiently good with everything. I would recommend ATH to anyone wanting to listen to various kinds of music on the move. DT660, I would recommend to a classical music lover who wants to hear colorful nuances in orchestral and chamber music without having to break the bank. I love my other headphones but I can say, with a peace of mind, that great sound doesn't have to cost thousends of dollars. It must be so that in this price range a consumer gets most for his money, no doubt. Any small improvement in sound will demonstrably cost the earth. Conclusion: We need an appreciation thread for DT660.