Hello Head-Fi'ers. I wanted to revive this thread with my impressions on the T51i's. I recently got a gig where I have to fly across the country on a semi regular basis and I needed some great travel headphones. I'm a Beyer fan and I push DT880's through a LittleDot at home, but that's not exactly a portable solution. I wanted something portable, something I could plug directly into my iPhone, and something that wouldn't look ridiculous walking around Seattle. Enter the beyerdynamic T51's. First off, as many have said, construction is top notch. They've got a solid feel, but they're not heavy. They come in a molded case that perfectly cradles the headphones, and there is a built in velcro pocket that can hold a couple bucks and my spare iPhone charger. It's designed and well executed for travel. A+ in my opinion. They're just perfect for slipping into your go-bag. These are my first on-ear headphones, besides the $8 variety that used to come packaged with a Walkman. Sound quality is incredibly impressive. The setup is extremely clear, well balanced, bass response is impressive, especially for the package. They're perfect for plugging straight into your iPhone and walking around a city, sitting on a plane, or even taking a phone call while out and about. When I'm back in my hotel room, quality appreciably improves when I plug them into my DAC/Amp (Macbook Air -> Audioengine D1). The biggest improvement I see is that I just get more power through the DAC and the Amp than I get through my iPhone, so the punch from the bass-to-low-mids is improved. To be fair, rest of the sound quality improvements are a bit difficult to judge, mostly because the ambient soundstage changes dramatically from an airplane or city street to a quiet hotel room. These headphones, even just directly from my iPhone, just start with such a very high quality sound. Now I believe it's a bit unfair to compare them to my critical listening setup, but here we go. They are not my DT880's. In my experience, the over-ear experience just provides a better soundstage than the on-ear's. The bass is fuller in my DT880's, and I think that some of the highs are better on the 880's, like when you're listening to crash symbols in jazz or something similar. But again, I think that's unfair because that's not what the T51's are for. I'll say that the phone call quality is much better on the T51i's than the DT880's Cons: There really is only one con, and it is big enough that I might not keep these. My right ear hurts after about 3 hours of listening and there appears to be nothing I can do about it. I've adjusted the band to adjust the pressure, I've experimented with slightly different headphone placement, but my ear just gets fatigued. This is due to the sensitivity of my right ear (left ear is fine. go figure.) and is not really a fault of the headphone, just that the design isn't going to work out due to the shape of my ear. I got these headphones almost exclusively for travel, and with pain setting in 3 hours out of a 5 hour flight, that's a problem. At the end of the evening while I'm traveling, I like to listen to an album or two while I'm getting work done and surfing the net, and the pain gets to be so much that I have to result to the built in speakers on my MacBook Air. Talk about a difference in quality. I got around it last time by bringing my old Sennheiser mid-tier noise cancelling headphones, but the goal here was to limit my travel gear. Plus, these beyer's are better than my old noise-cancelling Sennheisers. So, here's my bottom line. These headphones are fantastic. They are very impressive in all arenas that they were designed for--plugging directly into your phone, staying light on your head while not being obtrusively big, excellent sound quality for music, phone calls, and some portable critical listening. If they're comfortable for you, I can guarantee you will love them. However, if they aren't completely comfortable, there's not much in the way of adjustment. If you're looking for something in this area, I'd definitely encourage you to give them a try.