Pros: Excellent detail and instrument separation, good balance between bass, mids and treble; relatively lightweight and comfortable
Cons: unacceptable distortion, erratic highs, this is not worth $1,400, not even close
Please be advised that I am only writing this review to help other buyers. I am not trying to upset any T1 owners and it's my honest opinion. If you think it's unfair please state so in the comments and I can reconsider although I have enough experience with headphones now to know what I like.
First, let me note for the reader that if you google the three words beyerdynamic t1 deal, you'll see that every month or so an internet retailer sells brand new T1s for $750 to $780 (and these seem to be authorized retailers, for example one deal was from Buydig which is Beach Camera if I understand correctly, which is listed as an authorized retailer on Beyer's website; that deal even included free overnight shipping and no tax). These constant deals beg the question of why these "flagships" consistently go for mid-tier prices; The answer became apparent when mine arrived.
The only other top tier headphones that I have ever tried were the Sennheiser HD800 and the Audeze LCD XC. I preferred the HD800's sound signature, but I could appreciate the quality of the Audeze. For example, if you play the sound of a single guitar string being picked, you'll see that it's a noise which starts somewhat low in the frequency range, and rapidly, very rapidly, goes smoothly up in frequency until it reaches a high note. It takes a fast and capable driver to reproduce that well, and the XC could do that; it would send a chill up my spine. The HD800, well, I shouldn't have to explain why it's a flagship but let's just say its spatial imaging and magic are renowned.
The T1, though, is not even close to being in the neighborhood of those two. The best way I could explain the sound of this headphone in a relatable way, is to say they are an upgraded Shure SRH840. The way I tested them is to spend hours listening to and re-listening to my set of favorite songs, songs which I have played dozens of times and essentially memorized. I also listened to and relistened to very specific parts of songs, such as the sound of that guitar string being picked. The headphone was powered by a JDS Labs Objective 2 amplifier and I was generous with the volume, playing it at about 65-68 db ear level.
1. The bass, while relatively strong and booming, is distorted at the very low bass frequencies, which is less than you would expect from a flagship. There is a distinct way that the HD800 and especially the Audeze hit low frequency bass notes that distinguished them from mid-tier headphones. If you've heard it you know what I'm referring to (the SE846 is another example of clean undistorted low frequency bass). The T1s have plenty of bass, they're kind of boomy actually relative to what I normally listen to, but they hit bass notes in a subtly distorted and less than satisfying way. The measurement charts from innerfidelity objectively confirm the T1's bass distortion. Very common in $500 and under headphones; unacceptable for a $1,400 flagship.
2. The treble sometimes has what I can best describe as a subtle but annoying form of that "listening to treble on a cheap pair of ear buds, or a clock radio" effect. I'm obviously not saying it sounds like a clock radio, but let me see if I can put it another way. If you were to play a tone that smoothly goes up in frequency, it would not sound smooth on the T1. The T1 produces some treble frequencies at much higher DBs than others and this is not flagship sound. Very rarely it produces a particular treble frequency at such an unexpectedly high volume level that it causes that fingernails on a chalkboard effect. Good treble should be smooth, not jarring. Listening to classical music on an HD800 will exhilarate you. The Audeze wasn't as good as the HD800 in this respect, but it was no slouch and played smooth treble. When it comes time to play those songs and parts of a song on the T1, all it does is cause you to purse your face in disappointment. Again, if you read the innerfidelity charts for the T1 it's all there in objective science. The treble response is a mess with these, and my ears confirmed it. One important note about this issue: please keep in mind that one, just one, "fingernails on a chalk board" treble note can ruin an entire song for you. That noise stays with you. Mid-tier headphones either try to be airy, and have this effect or, more commonly, they just punt and roll off the treble. That's fine at that price range, but I don't ever want to hear that uncomfortable sound out of a flagship.
3. The midrange, to its credit, is very good, maybe even slightly better than the Audeze and the HD800. I couldn't definitively say which was better, but I had no complaints about the way the T1 reproduced voices, and I was impressed by the detail of its voice reproduction at times as it did things the other two could not do, in certain spots, particularly with a mid or deeper female vocals. So I will give it that. If I were just listening to people talk, or singing acapella in a middle range octave, I might choose the T1 over the HD800 and LCD XC.
4. Its detail is excellent, better than even the HD800. But since the HD800 was getting close to that "maybe this is so much detail that you're taking away from the joy of the music" territory, this may have gone over that threshold. I actually really like detail, but combined with the T1's other problems the excess detail was too much. But if you need to do an auditory detail spotting test, use these.
5. Instrument separation is also excellent for the same reasons as above. The way those instruments sound, though, is another matter as described above. But they're separated well.
6. Spatial imaging is, as expected, not anywhere near as good as the HD800 but better than the closed back LCD XC.
7. With its somewhat punchy bass and erratic treble, the T1 is more fatiguing than the HD800 or LCD XC.
A few other notes. For some reason people had me expecting these to be heavy like the Aude'ze but they're not heavy at all. They're in the HD800 territory in terms of comfort; very comfortable, so don't let that be an issue. They not made of fancy material, unlike the Aude'ze. They seem to have the build quality of your average $100 headphone. The cables are also not detachable which is very unusual. The case is a beautiful and compact aluminum. Very nice case. I uploaded a picture of the case so you can see. Much smaller and lighter than the needlessly big and heavy HD800 case and much nicer than the plastic audeze case. The T1 is also not unusual looking like those other two so you won't attract attention to yourself by wearing it.
If I could summarize by analogy, a Mercedes E-Class is a great car in its peer group, but if it tries to compare itself to S-Class AMGs, Bentleys and so on, it's a low performer. Same with this. It would get a higher rating if its MSRP were lower, but I have to rate it like a $1,400 headphone.
And to settle that mystery alluded to earlier, there is a perfectly logical explanation for why Beyerdynamic allows authorized retailers to sell this for $750, it's the only way they can clear inventory when trying to sell this for $1,400.