Ultrasone headphones are getting a lot of attention all over the internet due to probably very good marketing efforts. Before buying it for some reason I thought that I will be getting one of the best headphones on the planet in the price range.
 
After having it for a month or so and having at least 175 hours of burn in on them I still can't decide if I like them or not. If I had to describe sound signature of this headphone I would use one word: aggressive. It seems to attack your ears with very powerful bass and extremely bright high frequencies at the same time. Some will say that its not a bad thing and generally I would agree because usually I like such sound signature. At home I have Energy C series speakers that produce similar type of very bright and accurate high frequencies. I like them and dislike them at the same time. I know from experience that the sound produced by titanium or aluminum tweeters makes me tired. I know more about speakers than about headphone drivers, so I really wonder what exactly Ultrasone is using in these. In my car I have Focal KR speakers which are also very bright but not tiring at all, because the material used in the tweeter is kevlar which is a type synthetic fiber. Coupled with powerful woofer my car system has very similar sound signature but at the same time its very different.
 
Back to Ultrasone sound:
 
BASS: the bass is very punchy, powerful, tight and well controlled. However its not soft pleasant type of bass that I like its more on the aggressive side. Some may like it, some may not.
 
MIDS: slightly recessed, get better with burn in. I don't think that the main problem of this headphone is the mids, I think its the sibilance of the high frequencies and too powerful presence of the bass that somehow overshadow the mids. Comparing it to Grado SR-225 my impression was that Grados have much more forward mid and much more overall balance.
 
HIGHS: extremely bright to the point of being fatiguing especially at higher volumes. The highs sound very metallic, its a bit hard to describe but there is a particular sound in the highs which you can hear regardless of the track. However the highs of HFI 780 don't really make Rock/Heavy Metal sound good the best as its often the case with other bright headphones. Bass guitars IMHO don't sound as realistic as they should. Having said that I really enjoyed "Wheel Of Time" by Blind Guardian (orchestral version) in these. This is a killer track on my opinion.
 
DETAIL: this headphone reveals incredible detail, I guess this is why it has the reputation that it has. On detail level it outperforms many headphones out there including Grado.
 
SOUNDSTAGE: its quite wide, which makes it a lot of fun for some records. S-Logic is something that is hard to describe it needs to experienced. I think it does more good than bad overall. Again using Grado as reference HFI 780 soundstage is wider and surround effect promised by marketing is present indeed. One of the things I didn't like about SR 225 is that its very close to my ears. So Ultrasone really made an improvement with its S-LOGIC.
 
MUSIC: It sounds the best for electronic music. Vocals sound great, there is plenty of detail and to me everything aside from Rock/Heavy metal sounds not bad in these. However the sound seems to be kind of synthetic at times.
 
COMFORT: The headband is too big, they are clamping too tight (could be corrected by stretching), but no matter what you do, you still very much feel them on your head. The only thing I can say is that Ultrasone should really learn from DENON and Beyerdynamic because they are miles away from them in terms of comfort.
 
Like I said I can't make up my mind on these headphones, I have mixed feelings about them. My experience is ranging from ecstasy while listening to certain tracks to fatigue and frustration listening to others. There is no question that this is unique headphone and there is no question that it is a high quality headphone but its really not universal and not for everybody.
 
If you want to enjoy these the key is to listen to them at low volumes. At low volumes they are quite enjoyable. At higher volumes the sibilance of highs and too powerful bass at time can get very fatiguing.
 
UPDATE: After 300+ hours of burn in it becomes much better headphone, much more balanced, highs calm down, midrange becomes more forward. Initially I thought 150-200 hours are enough but it wasn't even close.

First of all I'd like to say that I listened to many headphones before getting this one and I own quite a few as you can see in my profile. I was looking for an ideal portable headphone and everytime I was unhappy about something. Here is what I went through: iGrado: good sound, but not comfortable, cheap looks, Beyerdynamic T50p: too expensive and still below DENON performance on my opinion, Grado SR 225: harsh, tiring, not very comfortable, virtually no isolation due to open nature with great sound though. Ultrasone HFI 780, not comfortable, too heavy, need amlification, not really portable. Etymotic HF5: can't complain about this one, but I just wanted bigger sound option. Philips SHP 5401: if you have only $40 bucks to spent go for this one. Beyerdynamic T5P ($1400): I will get attacked for this, but I really found them unremarkable unamplified directly from an iPod, DENON sounds better !
 
At some point I thought that there is no perfect portable headphone. One day I walked into Bay and Bloor Radio and listened to DENON AH-D5000, I was blown away and I thought that this is the ultimate headphone for me, however the problem was that its not really portable. But that was my introduction to DENON sound. Saw when I saw this one for sale I had to listen to it. I made a decision in 5 min. I have to say that D1001 has quite similar sound signature to D5000. So in short here is what I think:
 
COMFORT: It just can't get better, its super light, the ear cushons are super soft, even thought its not big it covers my ears completely. Japanese style - attention to every detail.
 
LOOKS: I gave it 5 starts.
 
BASS: The bass is punchy, well textured and very realistic, the only way I can describe it is its DENONs bass It has something pleasant about it. Its great for iPod cause generally iPod is lacking bass almost with any headphones.
 
MIDS: quite forward and present, not as present as in Grado for example, but not recessed at all as with so many headphones. Since I listen to lot of heavy metal to me if the headphone sounds good for heavy metal it is a good headphone. For some reason heavy metail music to me is the most difficult to reproduce properly cause it requires it all: the bass, the mids, crisp highs and great detail all at the same time. Not many headphones can do that. Some will excel in electronic music and suck for heavy metal
 
HIGHS: crisp and clear, bright enough but not too bright to be fatiguing. This is enough thing that I was looking for which is quite hard to find. Its quite amazing but DENON does it all
 
SOUNDSTAGE: one of the widest you will find in portable headphones, definetely wider than Grados.
 
I really can't find anything wrong with this headphone. Bravo to japanese one more time.

This is very cheap headphone so I didn't expect much from it and I have to say that I was pleasantly surprised. The design is great, its extremely light, super comfortable on the ears, you literally don't feel it.For $40 dollars Philips couldn't afford to spent a lot on the material, so the headphone is all plastic with thin cable which is obviously a weak spot. The cable is 2 meters long and comes with adapter (not gold plated)
 
Sound:
 
Bass: even compared to very expensive headphones I would rank it very high, the bass is soft, very well balanced, very well defined and doesn't seem to distort mids and highs. Exceptional bass handling. Big surprise. Philips claims to use some kind of special technology to produce this type of bass.
Mids: this is the typical weak spot of any cheap audio gear. I would rate the mids 4 out of 5 but this is only because I compare it to some expensive headphones, overall mids are balanced and quite present.
Highs: from the highs perspective the headphone is a little bit on the bright side but by no means it makes you tired like with Grado. 
 
Overall I have to say that the sound is very balanced, soft and pleasant, you can listen to them for long time without feeling tired. What surprises me the most is that this headphone is equally good for all types of music. Believe it or not but for Rock/Heavy Metal I prefer it over my other 5-6 times more expensive headphones. I rank it very high in cheap headphone category It has just right amount of everything for casual listening in the office.
 
Burn in: at least 60-70 hours of burn in required,  otherwise you would hear distortion across frequency range. But after the burn in you will fall in love with it.