Pros: Spacious soundstage, wonderfully airy, non-fatiguing yet sparkly
Cons: Stock cord and adapter, grainy, unnatural midrange, lack of sub-bass, overpriced
Design and Comfort:
These headphones are primarily composed of plastic and this contributes to the wonderful lack of weight and fatigue while wearing these. For the price, I would expect better quality material for the frame of these headphones but in reality, without the plastic, it wouldn't be nearly as comfortable. However, if you do buy this; keep in mind that these will not fare well if they're dropped (I've had them accidentally drop and the sound coming from the right cup became a bit wonky, so be cautious). These headphones were designed with looks of retro cars from the 60's and 70's in mind and though I wasn't sure I'd like the look, it's grown on me.
The large velour pads and supple leather headband make sure that it the HD 598's are very comfortable, which was well needed for my large head and ears. The brown velour pads provide comfort for hours and are spacious for larger ears and the headband ensures no certain pressure point of the head is pushed. These headphones can be worn for hours without discomfort; in fact, I often forget it's even on my head! The only flaw in the design is the cord and adapter which is cumbersome to say the least. It's terribly long for those who need a bit more portability and most just use the 3.5 mm jack. However, Sennheiser has come up with a replacement cable that is shorter and terminates into a 3.5 mm plug which I recommend but I do wish that they'd include it as a secondary cable with the headphones.
The treble of the phones is for the most part unfatiguing with a small bit of sparkle from 17-20 kHz. This is from a small peak and it adds a wonderful bit of sparkle and glimmer to drums and cymbals but can be a little sibilant in poorly recorded records, with vocals in particular. This can be remedied if you're overly sensitive to treble with EQ but I find this rarely occurs. (this is probably why the HD 598 is considered to be a bit bright)
The HD 598 are a mid-tastic phone, as their sound is more focused on the mids than other parts of the spectrum with a very forward presentation. Guitars and vocals are well-done with these headphones and they give a lovely pluck to strings. However, I've found there is an unnatural peak in the upper midrange of these phones, making vocals in particular sound a tad unnatural. Again, this can be somewhat remedied with EQ but it always comes off a little off.
The bass of these headphones are the least noticeable of the whole spectrum but is presented politely and accurately; it's very well defined and tight. However, it's always lacking some physical part of the bass. Upper and mid bass are plentiful but the sub-bass has a noticeable lack in amount of it. At times in bass-heavy recordings, the bass seems too polite in its presentation and as a result, the HD 598 are not especially renowned for their sound in club music, hip-hop and rap. The sub-bass problem can be partially remedied by amping and EQ but in the end, if you prefer a more bassier sound preference, you're better off looking for something else.
The HD 598's are pretty grainy for the price and some details are masked thanks to the uneven upper midrange and treble. However, the HD 598's more than make up for this with an airy, spacious soundstage that is perfect for those who want a more natural soundstage than that of the AKG's. The soundstage is balanced in width and depth, never claustrophobic yet never too thin in its presentation, providing a very realistic presentation of sound.
The HD 598's in short have a forward mid-focused sound presentation that can come off as convincing thanks to its large soundstage. The bass and treble take to the back burner and are relatively laid back but are presented well to provide a tad bit of sparkle with tight, accurate bass. These are great with acoustic, classical, rock and jazz. But, if you prefer a more exciting sound signature in the treble and bass or a headphone with a more V-shaped sound signature, you may not prefer these.
Are these headphones worth it for the price of $250? I don't think so as there are better phones in the same price bracket (SoundMAGIC HP200, HifiMan HE-400, Sennheiser's very own HD 600, AKG's, etc.) but these don't really need an amp or lossless music and this is why it shines. I've tried an amp or two and though I found it gave the HD 598 more body and slightly better bass extension and presentation, I found amping doesn't change the sound all that much.
These are still a great value, though maybe not at its MSRP. It can provide easily 80% of its full sound quality potential, un-amped on an iPod. More expensive headphones near this price range require an amp to drive them to their full potential and become more cumbersome. These don't need an amp and if you're bold enough to go portable, why the hell not? The price of these phones fluctuate from $150 to $250 online but I got mine on Amazon for about $190. Now that I've had these for a while, I would be reluctant to buy them again unless they were at a really great deal but ultimately, I don't regret my purchase.
Too many to name.
EDIT: Edited this review many times to give more in-depth information and to edit the previous text. Hope this time will be the last!
EDIT 2: Changed a lot of things in this one- feel differently about these then when I first got them. Still a killer set of cans, though.