Anyone ever carried out swept THD/IMD measurements and such, outside of headphone manufacturers that is? It sure sucks not to have more objective descriptions of cans' qualities - for example, bass and highs harmonic distortion would be interesting (bass quality has been notoriously difficult to evaluate correctly by ear), and then I'd sure like to see the influence of driver size on the all-important IMD (the more complex the music, the more significant this is). Waterfall analysis should be more common, too - the frequency response may not really tell about resonances that are present, but this'll do. (I've only seen a waterfall plot for the MDR-V6 so far.)

Headroom has the harmonic distortion graphs you seek, though unfortunately only with a fundamental at 500Hz:
http://graphs.headphone.com

This has been debated several times here. Short summay (search for longer version among various threads):

1. Measurements done properly are difficult: require expertise (understanding what to measure and how), expensive equipment (anechoic chamber, artificial head, proper microphones, proper analysis software), lots of time (several measurements, averaging between then, statistical analysis) and understanding (what conclucions can be drawn and what are limits of knowing).

2. Measurements data roughly below 500Hz and above 8kHz are mostly useless (unless done professionally and right). Measuring one one's onw head gives more of a subjective measurement data than measuring on an artificial head (with a proper pinnae type).

3. Objective measurement data (even when done by professionals and right) and subjective evaluations do not always correlate well. The reasons are not fully understood by researchers in the field.

4. Objective measurement data cannot be used to decide on how the headphone sounds to a person (although some glaring faults can be perhaps verified with the co-operation of both listening and measuring). This can only be done by listening.

= music is not graphs, headphones are not measurements and badly done measurements usually misled/lie more than tell the truth.

IC. You probably mean threads like this?

Point 1: So one would need the kind of equipment that, say, the guys at Headroom use. OK, makes sense.

Point 2: <500 Hz because of seal issues I guess (particularly in closed cans), and >8 kHz because of ear canal etc. influence?

Point 3: %§&/!"%! I guess that's because everything and anything is involved here, harmonic and anharmonic distortion, IMD, reverb/resonance, frequency response, and then point 2, plus the whole stuff gets processed by that strange grey mess that nobody fully understands. Constructing headphones must be, well, rather tricky at least.

Point 4: Frequency response and waterfall plots can certainly tell a lot about sound, but like you write one needs to correlate this with listening experience.