Pros: Great comfort, solid build, removable cable, genre versatility, rich, lush & full sound, kickass imaging, natural soundstage, scales with amping, FUN!
Cons: Stock cables, rollercoaster treble, fragile paint job, overpriced at RRP but a great deal heavily discounted or used
After my disappointing experience with the HFI-580 that left me thinking I would never, ever buy another Ultrasone headphone ever again, I continued on my search for a similarly "full" sounding headphone. I really liked the way the HFI-580 did bass, and it's mids were fine (not amazing, but fine). But the incredibly fatiguing treble response and the bad comfort made it simply unacceptable overall. One day I was perusing some frequency response charts, and came across the HFI-2400s. I was actually quite intrigued by what I saw, and a little bit excited, thinking that I may have found what I was after. It had the moderate midbass emphasis of the 580, but with even more in the upper bass, the mids looked as though they were placed roughly the same (a tad recessed, but not problematically so). The major difference, however, was in the treble. Whilst it was less even than the 580, it was clear that it was a significantly darker headphone, which sounded like it was just the ticket for what I needed.
The HFI-2400 usually retail for around the $300 mark, at that price they are up against some quite stiff competition, even if they are the HFI series flagship. To be honest, for that price I would likely have (and probably still would) go with something else. However, in my case, Addicted To Audio had this model drastically discounted from the usual $310 they sell it for to an amazingly low $150, yes, $10 less than what I paid for the HFI-580. I can only assume this was because they weren't moving the units, as this a more obscure headphone compared to the more popular offerings of it's price range. I jumped on it almost immediately, and I'm glad I did, because for $150 this is about the best you could really hope to do for a brand new, open, circumaural headphone.
The build quality of this headphone is of a very similar level to the HFI-580, which is good because that is a solid headphone. The plastic is all very sturdy, the aluminium on the cups makes the headphones feel high end, and level sturdiness they give off when in your hands is good. The major area where the 2400 are of higher quality is the padding. The HFI-580 has the worst pleather on any headphone I've owned. It was poor not only from a quality perspective, but it was one of the major factors that made the 580 such an uncomfortable headphone. The 2400, on the other hand, uses black velour padding, which is far, far superior. It's very soft, it looks great, it doesn't get all oily and awful in the heat. The 2400 also has a removable cable, which for any headphone is a great bonus since it really means your headphones are likely to last longer since a dead cable doesn't = dead headphone. However, I'm really not fond of either of the cables that comes with the 2400. The main cable is a 3m cable, which for me is just too long, and the 6.35mm jack is a bit cheap and ugly looking. The other the strange inclusion of a portable cable terminated in a 3.5mm jack. I say it's a strange for two reasons. Firstly, this headphone isn't at all what I would call portable, and if you're considering this thing for portable use I think you're out of your mind. Secondly, it measure approximately 85cm long, which is just barely enough to go from the headphone to your media device in your pocket, with basically no room for any slack. It's just too short, it needs to be another 20-30cm longer, not that I would use it anyway since using the 2400 for portable use is like using a school bus for off-roading. So neither cable suited me, however the perfect cable for this headphone is the V-Moda audio-only cable. The 2400 takes 3.5mm (Thankfully, it's always preferable to the 2.5mm variety), so the V-Moda cable fits just right, sits in there nicely with not a hint of looseness or falling out. Not only that, but the black and grey weave colour option of the cable that I have goes flawlessly with the 2400's colour scheme. I highly recommend this cheap upgrade for the 2400. The only problem with the build is that the paint job is slightly fragile, it's not difficult for it to get rubbed off against something, so be careful with that.
Comfort is quite good for me, wayyyyyyyy better than the HFI-580. As mentioned, the velour pads are far and away superior to the rubbish pleather that plagues the HFI-580, but the padding itself also appears to be softer, which works wonders for the headband. It's the same size of padding, but because of the softness and material, it's just so much better. The earpads tell the same story, but they also benefit from just being larger in size, a much more generous sized circle shape than the more cramped oval of the HFI-580. Clamping pressure also appears to be lighter on these headphones. The HFI-2400 is more comfortable than the HFI-580 in every single way, and definitely qualifies for all day use for me, no problem.
In terms of sound, they pleased me instantly... providing they're amped sufficiently. I've heard people say that they don't need amping, but I honestly don't agree. I notice the sound quality decreases noticeably (not dramatically, but it's definitely there and quite obvious) when plugged into your typical portable devices, or a computers audio jack. From the Audio GD NFB15.32 they sound great, and they also sound pretty good out of a stereo receiver's headphone jack. When they're amped well, they sound great, this is what I hear:
The bass response is fairly generous, but not offensively so. There is a strong mid and upper bass hump, which is very much what I'd describe as "fun" bass. Drums benefit from this greatly, especially aggressive drum blasts in metal, it's very satisfying to listen to. As is common for "midbass hump" type bass responses, the sub-bass suffers from roll off. It's certainly not Grado level, where the sub-bass almost doesn't exist what-so-ever, but it definitely has significantly less authority than the rest. Compared to the HFI-580, the bass lacks a little bit of punch, which is an expected difference between a sealed and open headphone. That's not to say on punchy tracks it will sound weak or underpowered, not at all. If anything that's what the HFI-2400 does best. It's quite warm and rich sounding, very pleasing. Some users may find the bass a tad slow for super fast, hectic, crowded sounding music. I find it depends on the mastering, if it's well mixed and mastered the HFI-2400 will sound very dynamic.
The midrange is quite smooth, though a little recessed. There's a particular lushness to it that I'm quite fond of, it's very satisfying with acoustic guitars in particular. Some will feel that the midrange smoothness is too polite and lacking in excitement or the "crunch" factor. Despite the slight recession, I wouldn't call it problematic. Vocals aren't placed back so far that they're lost or buried, though because of the nature of the mid-bass to lower mids hump, male vocals shine through with more authority than female. Clarity is quite good in the midrange, with good definition, but as I said it's quite smooth so that very last bit of micro detail isn't quite there. Whilst it's not perfect, the midrange performance is satisfying, and really quite admirable for an open headphone with such a strong bass response.
The treble is the part of the HFI-2400's performance that I find to be a bit problematic. However, I should make it clear that I don't find the treble response to be poor, not at all. It's just a little weird. I say this because the treble is really rather uneven:
It's a real rollercoaster! It really does sound strange sometimes, in that it manages to be both bright and dark at the same time, I've never had that with a headphone before. Usually they're quite clearly one or the other, on some level at least. Ultrasones are known for being bright, and as my experience with the ear piercingly bright HFI-580 indicates, too bright for many. Luckily, the bright spots are no where near as bright as on the 580, so at no point did it become too fatiguing for me. But, I just can't quite forget about the uneven nature of it. It results in certain things in the treble regions to be oddly placed over others. For my tastes, I think the most problematic thing with it is the sharp dip at 2500k. I think that leaves things like guitars lacking in texture a little bit of body and definition.
Imaging is where the HFI-2400 shine, in my eyes. These are really the first "well imaging" headphone I've owned, and I really don't want to go back. Coming from what I've been used to, the most noticeable difference was that grand, spacious music didn't sound anywhere near as limited. Whether it's classical or "epic" metal, the HFI-2400 convincingly portray spacial cues with a moderate amount of space (it's not a huge soundstage) but great depth. This is one of the qualities that makes it a good recommendation as an all rounder headphone, because gaming and film benefits quite noticeably for the imaging abilities of the HFI-2400.
Everything taken into account, I think that for the bargain price I paid for it, the HFI-2400 is simply kick ass, it's about as good as you could ever hope to do for the price, in my opinion. However, I think that the full price of admission ($300) is really too much. If I had $300, this really wouldn't have been my choice. I actually got the Denon AH-D2000 just recently for $300, and I find it to be a noticeably better headphone in essentially every regard. So, I guess I'm technically saying that they're overpriced. However, if you can get one used or heavily discounted for under $200, I think it's a very good choice.