To compete in the premium-priced (>$100) segment of the headphone world--where Beats enjoys over half the market share--untold numbers of headphone makers have attempted to sell Beats-inspired headphones, some even more than just inspired, looking like outright clones. Others, however, have taken a completely different tack to help earn their premium prices, making use of luxurious materials and design, eschewing the Beats-trendy plastic cuff look in favor of ritzy metal and leather sculptures. The Bowers & Wilkins P5 and Philips Fidelio L1 come to mind. And you can now count Sennheiser among this latter group, with the introduction of their brand new MOMENTUM.The $350 MOMENTUM is a closed, circumaural (around-the-ear) headphone designed to be used the way most people in the world today seem to be using their headphones--plugged directly into mobile phones. Sennheiser designed the MOMENTUM to be easy to drive by a mobile phone, with a low 18-ohm nominal impedance, and a relatively sensitive nature. Increasing its phone-friendly appeal is the included cable with iDevice-compatible three-button in-line mic/control. (The MOMENTUM also comes with a plain audio-only cable.)The MOMENTUM comes with a very nice hard-side carrying case covered in what feels to me like a high-thread-countbrushed fabric in a very unique (unique for a headphone case anyway) rich brown color. One particularly nice detail of the MOMENTUM and its carrying case is the ability to carry the headphone in the case. To make this doable, Sennheiser designed the MOMENTUM so that the cable's headphone-side plug inserts very deeply, leaving just a wee bit of plug body sticking out from the earcup. I've found most of the headphones I use with detachable cables require the cable to be removed while in the case, and one of my pet peeves is having to fumble with the cable when removing the headphone for use or putting it away.As best I can recollect, there hasn't been a Sennheiser headphone so strongly promoted for its style and non-audio-related aspects--coupled with minimal specific information about its sonic bits and pieces--than the MOMENTUM. Given the MOMENTUM's beautiful style and swanky materials, I can't say I blame Sennheiser for playing these aspects up to the marketits targeting.The MOMENTUM's stainless steel headband has a very nice brushed finish that is as well-executed on the less visible inside of the band as on its outer surface, which is representative of the attention to detail that's obvious throughout the MOMENTUM's construction. It's the type and quality of brushed finish that you'd more expect to see on a fancy stainless steel watch than on headphones.The in-line mic/control and the unique variable angle mini plug's body also seem to be made of stainless steel. By the way, this bendable plug is a vast improvement over the comparatively huge twist-type hybrid straight/angled plug that the Sennheiser MX 980 and some of its peers were equipped with (in case you were worriedwas the plug I was referring to).The leather covering the top of the split-type headband is a beautiful, rugged-feeling hide, and the leather on all the surfaces that touch you has a far more supple hand. To provide the opulent skins, Sennheiser actually turned to famed English tannery Pittards. (And, yes, it's all real leather, and it's also sweat and water resistant.)In addition togorgeous, the MOMENTUM is alsocomfortable. The super-supple leather earpads are circumaural and pillowy soft, the clamping force very mild, and the feel on the head feather light. I can wear the MOMENTUM for hours at a stretch, and have done that many times since its arrival. When it comes to portable headphones, the importance of this level of comfort cannot be overstated, because, frankly, most of my favorite portable over-ear headphones are supra-aural (or-ear), and generallycomfortable enough for non-stop hours-long wear. (Again, the MOMENTUM is circumaural, or-the-ear.)So the MOMENTUM is a visual and tactile treat, and it's extremely comfortable; but what seems an almost single-minded emphasis on its looks and materials might have you worrying about its sonic performance. Well, the Sennheiser MOMENTUM is,to my ears, a very good headphone for what it is, and for the market it's going after, and I have enough background to know that there was much consideration, tuning and effort behind the MOMENTUM's sound signature, not just its looks.So how does it sound? Like many headphones that more specifically target the general premium consumer market (as opposed to diehard audiophiles), the MOMENTUM is a headphone with some bass emphasis. The boosted bass sounds to me to be rather more wide-band than the more focused, milder bass emphasis of, say, the V-MODA M-80 (which is one of a few of my reference portable over-ears). It's enough of a boost (and wide enough) to push the MOMENTUM's tonal balance out of reference-class, to my ears, but slots it almost perfectly into the type of sonic signature I prefer for a headphone I'd choose for on-the-go use, where I prefer some bass emphasis to help accentuate the music's rhythm in the din of the bustling world around me. In consideration of its level of boost, the MOMENTUM's bass still has adequate control, but ideally I'd prefer it somewhat narrower in band, a bit tighter, and more focused on lower bass.Everything above the MOMENTUM's lower range boost is rendered very nicely. Versus the Bowers & Wilkins P5 and the Philips Fidelio L1 (two other headphones I enjoy for on-the-go listening), the MOMENTUM has more clarity for me through the mids, and more treble detail and shimmer. Like the P5 and L1, the MOMENTUM has a clear tendency toward a thicker overall tonal balance, but remains reasonably detailed overall, and would be my overall sonic preference of these three luxury headphones.While I easily recommend the MOMENTUM as an on-the-go headphone, I'd be less quick to recommend it as a reference headphone for more critical listening, unless your personal reference sound tends toward a bass-heavier signature, in which case you'd probably love the MOMENTUM. My three personal reference portable over-ears are currently the beyerdynamic DT 1350, Sennheiser Amperior and V-MODA M-80. Though these headphones all sound different from one another, all are more generally even-handed--more accurate overall--than the MOMENTUM, possessing the types of signatures I can more easily settle into for more critical stationary home and office listening.Of these, the one that Head-Fi'ers have asked most about in comparison to the MOMENTUM is the Amperior, some speculating that perhaps they use the same driver. Sennheiser has confirmed that they do not use the same driver; and, to my ears, they have about as much in common sonically as they do in appearance (which is to say not much in common at all). Though the Amperior tamed some of what I feel is a sometimes too-aggressive Sennheiser HD 25-1 II treble, the MOMENTUM is even smoother to me up top, from the middle highs on up (and that can be either a positive or negative trait, depending on what you like). But there's more than that separating them, the MOMENTUM's more emphasized bass and fuller mids completing the dissociation for me between these two. Here's what I'll say, then: If you've heard the Amperior (or the HD 25-1 II which, again, is a bit more treble-peaky to me than the Amperior)--and you thought it was too aggressive up top, and you also wanted more emphasis on the low end--then the MOMENTUM should definitely be on your short listAs far as isolation goes, the MOMENTUM is comparable to the Amperior, which is to say quite good, but short of the level of passive sound-deadening of the beyerdynamic DT 1350 (which is still one most isolating passive over-ears I've used).For me, the new Sennheiser MOMENTUM is a super-comfortable, beautifully made headphone that will likely take its place ahead of the Philips Fidelio L1 and Bowers & Wilkins P5 as a gorgeously built, super-stylish headphone with the bass emphasized sound signature (and good overall clarity and resolution) that I'm looking for while on-the-go. And with my current lifestyle, that's an important role to fill with me, and one that gets a headphone a lot of time over these ears of mine.Though it won't take the place of my current portable reference over-ear headphones for more critical listneing, I find myself grabbing for the MOMENTUM instead of those more than I thought I would, in large part because of the MOMENTUM's comfort--and, yes, I admit because of its style, too. Again, though, ifpersonal preference is generally for a thicker, bass-emphasized sound with good overall detail, the MOMENTUM might just be the reference headphone you've been looking for.And if a headphone's styling is a key consideration for you, I don't think I have to do much more than to show you some photos of it to be sold.I applaud Sennheiser for choosing to goroute to appeal to the premium consumer headphone market. For its intended use and market, the MOMENTUM is an excellent sounding headphone, as well as a leather and steel design oasis in a desert full of plastic lookalikes.