Yeah that metallic treble is a problem with all Ultrasones I've heard/owned to varying degrees. It's like a cyborg approximation of real music. It's not that noticeable if you listen exclusively to EDM, but put real instruments on and things sound off in a hurry.

I wonder what causes that because I don't think I've run across that in another headphone yet it's characteristic of all Ultrasones.

My subjective impression some what matches the others in this thread as well. Although I do find the bass to be rather pleasant personally because I just like that kind of sound. (I must admit I do EQ up the bass in the car stereo) The treble is really getting fatiguing though, when I first got the PRO900 the treble emphasis did feel somewhat pleasant with my music, but now it just gets annoyingly loud.

The HE400 is looking more and more attractive now....

I have (very briefly) owned the Ultrasone Proline 2500 and selected it by the original graphs sent to me by Ultrasone on request.

It is quite flat and had good hopes it would sound really good as well.
Sounded 'boomy' and the highs were anything but pleasant. 
Not too much of it, but most of all not 'nice'.
I suspect a lot of effen' ringin'.


This is the plot of the 900 taken by Ultrasone.
   Nauseating by the looks of it eventhough it was recommended to me by a bass player who said it was one of his favorite headphones.
a VERY CLOSE resemblance to Purrin's plots, so hat's off to his measuring skills.

I wasn't interested in the uber-expensive edition line but FWIR it sounds 'better'.
Never had the pleasure of hearing those.

The 2500 and 900 indeed aren't that dissimilar on closer inspection.
It's the vertical scales that make them look quite different.
The highs of the 900 should be 'better' in FR quantity than the 2500 even, perhaps with some EQ in the lows...
Ah well, the ringing will still be there..
It was the 'overblown' bass, and highs that killed it for me, sounding grainy and rough.
I held on to it for a while and gave it a few chances but was gone within 2 weeks already.

2500 and 900 mids (between say 200Hz and 5kHz) aren't that bad within 5dB, though the 2500 has less dips.
Pro900@50Hz =+15dB, Pro2500@50Hz =+9dB
Pro900 between 5k and 20k =+ 3dB (average), Pro2500 between 5k and 20k =+6dB (average)
The 'flatness' of the 2500 appears to be an optical illusion. 

I also have plots for: HFI650, HFI700, HFI780, HFI2200 and Pro750 for those that are interested.