Here's some interpetion of the XB900's FR measurement, I added the "average" frequency amplitude as orange line at which you can compare roughly which is recessed (below line) and what is emphasized (above line). First should be noted different kinds of measurements lead to different looking graphs, in this case, the measurement seems to correspond more to "goldenears" site measurement where the highs should actually be on the same level as mids to be concidered "neutral". If you would see the FR measurement showing up on Tyll's site the 8kHz area or so in his measurement I can garantuee you won't be on the same level as 550Hz area but will be on a lower amplitude, if it was it would be very bright sounding, it's just different way of measuring and the reader will have to know how to interpret the difference but it's worth pointing out.
Anyway I read aprox 10dB bass boost (peak), ~9dB average boost in this measurement in the 20 - 200Hz area which I generally concider a the area that should be measured for bass. This can be compared to 15dB boost in XB700 in 20 - 110Hz or so range while the XB900 extends all the way to almost 200Hz before it rolls off, which is where it's already safe to assume, XB900 will feature significantly punchier bass than XB700. It can also be compared to XB500's 15dB boost in the 20 to 300Hz range (already approaches the lower-mids which leads to muddy midrange as the bass isn't rolled off soon enough, generally higherend bassy headphones roll-off by at least around 200Hz for a good reason which Sony has obviously learnt from XB500 looking at both XB600 and XB900).
The rest of the range looks muuuuch better than previous XB headphones, besides getting slightly less bass quantity (probably in favor for quality) too, the mids and highs are very nicely balanced in XB900, almost neutral by this measurement throughout the whole range, obviously the 9~10dB bass boost will still make the mids & highs seem lower in level but if you'd EQ down the bass it would sound very neutral most likely but even so here I expect a significant step-up in the mids & highs detail versus XB500 & XB700 due to the shape of the bass curve which hints a more tight & punchy bass versus the previous series. That there's a variety of aprox +/- 3dB throughout the entire mids & highs range is really promissing, from my experience aprox lower than 5dB varieties are generally pretty inaudible and flat sounding. Another point worth pointing out is the sliiiight bump at like 500~600Hz range at which range XB700 for example had a bit of a dip and where it was the most recessed in the midrange while the XB700 versus XB500 sounded a bit more distant in the mids, it looks like XB900 definitely won't have as recessed mids as XB700. Only the 700Hz - 2 kHz range is slightly worrisome, there I had rather preferred seeing it more flat, aprox +5dB compared to that, a little bump on the EQ at 1kHz and 2kHz will probably do very good for this headphone.
Of course this is just one measurement and from an a bit unknown site so we don't know how "accurate" their measurements are like but assuming they'd be pretty accurate this FR measurement is very promissing for an "XB" series.
Edited by RPGWiZaRD - 9/10/12 at 10:07am