I bought these (at £150) expecting much but was shocked by how far they fell short of even competency.

They are very uncomfortable, badly designed and the sound is really nothing special. Whatever I did I couldn't get them to sit flush on my ears so that only the top third of each ear cup would rest properly on my ears, the lower part would stick out away from my ears in a most unnerving fashion - remarkable! - I've never had that happen in a headphone - the effect was actually comical! After struggling with them for a while I finally managed to get a decent seal on my ears by forcibly pinning them down, readying them for an audio evaluation. But by that stage they had become instruments of torture as the steel headband - very thinly covered by bit of ineffectual padding - had started to sink its way into my skull. I had endure quite a bit of pain in order get an idea of this headphone's audio abilities.
 
The sound is basic, by that I mean you get music reproduction at a most rudimentary level - music just blares out at you with little or no finesse; very shallow sound-stage, bright, big but crude sounding and unnatural. I didn't spend too much time listening to these for the above reasons so I leave the audio evaluation at that, and to be honest, I felt that it didn't deserve more time spent on it than was necessary.  

Don't be blinded by the science bit - a typical marketing trick - namely the "DSV (Dual Sided VortexTM) technology" and the "SpaceTM technology" (patent-pending no less), these have a sound reminiscent of below par £70-£80 headphones and no more (I'm thinking Grado headphones which they most resemble and which you're better off buying). At £150-£700 (yes, the price has varied or varies that wildly, currently £500 (!) as I write) it's ridiculously bad value for money. It's this exorbitant and outrageous price that Flare Audio are asking for this headphone that prompted me to write this review; if this had been a £50 headphone my expectations would have been low enough not be bothered too much by its sheer awfulness. I think most, if not all other headphone manufacturers would be embarrassed to release such an ill-conceived and badly executed product. I just hope for their own sake Flare Audio recall these headphones, goes back to the drawing board and design a headphone fit for public consumption.
 

Needless to say they were packed up and sent back pretty quickly.

Let me start off by saying that I had the previous version of this headphone - the X1, and I got rid of it because of the excessive bass output that spoiled what would have otherwise been a very good headphone. I was hoping that the X2 would correct the faults of the X1 but all I perceive are very minor improvements in bass definition and slightly improved sound-staging.

The bass continues to dominate in the X2 at the cost of mid-band and treble quality. In bass heavy music, it is the bass that shouts the loudest and makes sure you 'get the point'. It's fun at the beginning, but soon becomes tiresome and for me at least is a right switch off. Vocals often lack smoothness and naturalness, and the glassy tone in the upper midband/treble heard in the X1 is still there in the X2, but now there's added graininess. As a consequence, the sound sometimes lacks resolution and refinement. Imaging also suffers as voices, for example, become 'splashier' and are not as defined and distinct as they should be. The whole sound is a curious mixture of big bass and lower mid-band warmth, and upper mid-band and treble brightness or coarseness; there is simply no integrity to the X2s sound.

Although it lacks refinement in reproducing a lot of music, ironically in Classical music - where bass tends to be much less prevalent - the X2 can actually sound very nice. Sound-staging is quite deep and wide and instruments are placed fairly precisely. However when the music gets busy and bass notes start to prevail, then the presentation starts to becomes 'in your face' again; the X2 can't resist unleashing the testosterone filled bull that is its nature.

So if you like your music 'big' sounding and don't care much for refinement, precision and musical insight, then go for it. Otherwise steer well clear.

I've recently sold the X2 and bought the Sennheiser HD600 again - for the third time - and again I'm reminded what a truly great headphone it is. The qualities I was missing in the X2 are finally here in the HD600; refinement, naturalness, high class resolution, smoothness and a finely judged tonal balance.

The pretender - the Philips X2 - has been imperiously brushed aside.

My time with the HD650 was short: bought on Amazon and returned 6 days later.

Prior to serious listening, I 'burned-in' the headphone for 48 hours with constant pink and white noise. This did improve the sound, firming up the bass and eliminating some perceived hollowness.

The thing that struck me first about the sound of the HD650 was its sumptuous smoothness. Vocals especially had this syrupy sweetness which many enthusiasts will like about the HD650, but for me just masked the natural characteristics of the human voice. I find it difficult to understand why recording studios would use this headphone, as Sennheiser claims in its advertisements, when vocal presentation especially, is so obviously coloured. When I listen to a headphone I want instruments to sound as close as possible to 'real life' instruments, timbre being particularly important. The HD650s do manage to preserve some accuracy in instrumental timbre but simply fail on the human voice, where neutrality is traded for chocolate-smoothness.

The overall sound is indeed warm and smooth which is sometimes appealing, but together with the relaxed, sometimes listless presentation, music is robbed of the vitality and vivacity it needs. This does make the HD650s the headphone to go for if you just want to listen to music in comfort for hours on end; but some of us want some energy and excitement - when the music demands it - which these headphones frequently fail to deliver.

Bass is quite deep and usually remains fairly tight, but sometimes sounds soft in some music, which is I think is a consequence of the overall 'plump' warmth of the headphone. And again due to the - for me - suffocating smoothness, the high treble sounds blunted; the HD650s never manage to reach the heart-stopping heights that the female voice especially, is capable of.

As for other qualities...imaging is good but nothing special, nicely formed but by no means holographic. Sound-staging is very good, in fact it can be ruthlessly revealing of poor quality source material in that regard; some of my less than perfect recordings had a 'gap in the middle' effect on the HD650s which was not apprarent on other headphones.

Detail retrieval is excellent. The HD650s are able to pick up background and ambient sounds with ease and elegance, but musicality always taking precedence over outright detail-scavenging.

As for build quality, really disappointing - masses of plastic that has an uneven appearance in certain lights; and they look as if they could easily break or crack if dropped on a hard surface or accidentally sat on.

So I recommend this headphone to someone who a favours a warm, smooth and 'friendly' representation of music. But those who want crave neutrality, realism and energy - look elsewhere.

I came to this headphone after 10 months with a Philips X1. Although the X1 is a good headphone, towards the end of my time with it, I become increasingly dissatisfied with its sound signature.
I stopped listening to music regularly and for a long time I didn't realize that the X1 was to blame! Although every time I used it I would be impressed by its abilities, the sound was ultimately just too bass orientated for me; and also the treble tended towards a glassy tone in some music. So after some research, in steps the K612 Pro. Now this headphone is quite different. Less bass but better proportioned, the sound is more natural with a pleasing delicacy to the sound, particularly the treble, that although a little dry, is open, articulate, never harsh or sibilant and only very slightly rolled off at the top. The mid-band is detailed, expressive and free of any nasty colourations, however the upper mid-band does have a tendency towards the already mentioned dryness of tone, but that's really a minor quibble.
 
The headphone images very well and keeps various musical strands from merging into each other even in busy,complex mixes. Sound-staging is good but not a particularly strong point of this headphone, it keeps everything at a medium distance; not very deep or wide. However that suits me fine as I find headphones that are very adept at sound-staging somewhat artificial in their representation of the music, not really true to life at all.
 
The bass on these headphones is just right for me; tight, fairly punchy and ample amounts when called for - okay, perhaps a smidgen more and it would be perfect, but considering this is a £100 ($160) audiophile (or audio enthusiasts, if you prefer) headphone, I'm generally happy with it. Anyway, bass quality is more important to me than bass quantity and the K612 Pro delivers on that front.
 
In respect of amplification; you'll need a fairly powerful, preferably dedicated, headphone amp. With low power portable devices and laptop headphone outputs you will not get sufficient sound quality or volume. So if you don't have a suitable amp, you should factor in the cost of one if you decide to purchase the K612 Pro.
 
In respect of comfort; there are no issues at all, not for me anyway. The headphone is very light and the clamping force of the earpieces is fairly gentle, the leather headband sits gently on the head too, and the cushions which are soft and pliant don't cause (me) any irritation.
 
So summing up, I heartily recommend this headphone. It performs well in all areas and shines in some, such as neutrality and resolution. I doubt you'll find a better headphone in its price range.