Originally Posted by Bizzlebin
Ok, you got me there, jcx; even soundstage can be adjusted on a given set of cans using hardware or software, even free software. So that potentially narrows the list down even further: are there any things that can't be changed on headphones other than THD? What are the implications of this?
I may be mistaken, but there are some limits when it comes to external processing/filtering (of whatever type) and changing radiation patterns. For example, you can never make the KSC75 present a planar wave to your ears (like you'd get from an electrostat or ortho). Just like you can't create the S-LOGIC effect without manipulating the enclosure design of the headphones (but afaik, you *could* create the effect if you spent the time fabricating the enclosure (or just frankenstein'd an Ultrasone)).
That, coupled with the inability to solve very large resonance problems, are probably the biggest issues you have along with the individual characteristics of the driver (like THD and phase).
Everything else you should be able to affect with precise/clever enough filtering/processing, and enough time. If you allow physical modification to the headphone as well, then yes you can probably change everything (in the sense that, you could easily place whatever chosen driver into whatever enclosure you like, following whatever orientation you like (even exotics, like S-LOGIC and Auranomic)) except for the wave front presentation (in that, again, you can't make the KSC75 radiate in the same pattern as an O2 or HE-6, even if you get the FR to look identical or very close).
I'm just basing all of this on speakers - you can get "flat and clean" from all manner of speaker designs assuming you deal with acoustic issues and make use of equalization, but you can't fundamentally change their radiation patterns or alter the limitations of their chosen design paradigms - unless you can dramatically modify the enclosures or change transducers (at which point you're talking about different speakers imho). For example, the Sansui SF speakers will always radiate in a 360* pattern, and without changing their enclosures fairly dramatically, you can't do away with that. However, you could place them in a room with treatments designed to complement that radiation, and EQ designed to address both their own FR problems and the FR problems resulting in the room, and likely end up with a "flat and clean" image at the seated position. I think you can do the same thing with headphones, but I think there's still going to be some fundamental differences due to radiation/dispersion due to driver arrangement.
This all assumes power handling is a non-issue, and that your amplification and output equipment can survive the results of dramatic EQ curves that may see huge increases in overall demand without resulting in tons of distortion or damage. This probably isn't too dramatic of an assumption methinks.
It would be neat to try the SVS out with a few different pairs of headphones.