In terms of tonally balanced    ... that's the Oppo PM-1. I mean, there's really no better way to describe it.

Oups... Do you mean they went a bit too far with taming the highs that no eq will wring the stuff back / too muddy to ever resolve like an hd800?

I really think the lack of detail and treble roll off are due to a heavy-ish diaphragm.  I don't think EQ will be able to help in the detail department since it doesn't seem to really be a matter of FR.

Do you mean the LCD3 or HD800 ?

references used for comparisons in the post below:
http://www.innerfidelity.com/images/AudezeLCD3sn2312454.pdf
http://www.innerfidelity.com/images/SennheiserHD800.pdf

I don't see any heavy diaphragm roll-off in the LCD3 plots anywhere.
I do see shelving and a peak at very high frequencies.

Tyll's needle pulse plots indicate the LCD3 is faster than the HD800, but they also indicate the HD800 is better damped.
The faster reaction of the LCD3 membrane doesn't seem to indicate speed problems due to weight.

The diameter of the diaphragm-ring and the rigidity needed (seems to come from its shape ?) as well as the weight of the large copper voice-coil won't make the HD800 moving mass any lighter than that of the LCD3 diaphragm. 
This membrane doesn't need to be rigid to transfer the mechanical energy into sound waves as it is driven over its entire surface and thus can be thinner and lighter .
The HD800 ring must have a minimal rigidity in order to transfer the movement energy of the voice coil to the ring into sound waves.

The 300Hz squarewave edge of the HD800 appears to be (much faster) but suspect this is an optical illusion caused by the overshoot which in itself is caused by the raised treble.

In the FR plots from Tyll (especially the raw plots) it would appear the LCD3 has better extension in the highs where the HD800 rolls of gently.
This could indicate speed problems due to weight aren't an issue.
The HD800 seems more position dependent than LCD3 (which makes sense to me)

Interestingly the distortion in the lows (at higher SPL) indicates the LCD3 is superior there as distortion lowers from 90 to 100dB SPL where the distortion increases in the HD800.
This could indicate a better linearity and possible larger excursions the LCD3 can make.
This is supported by the FR by the way.

Phase response of the LCD3 is far superior to the HD800 and the slight but gentle slope in phase response of the LCD3 also doesn't point in the direction of a too heavy membrane, in this case phase would lag more as the sonic output would fall behind of the electrical stimulus.

I see no reason not to think the LCD3 could not benefit from an EQ in the treble and know the LCD2 responds quite well and this one seems to have a heavier diaphragm acc. to the manufacturer.

These 'technical' analysis of Tyll's plots say little of how they are perceived by person A or B and comfort (to me) is also important which is clearly in favour of the HD800. One of the most comfortable headphones around for me.

To me they are BOTH excellent headphones, that sound VERY VERY different in stock form, and both may benefit from modifications and/or EQ.

I agree with Anax that all headphones out there can and do benefit from mechanical (and/or electrical in my POV) changes.
Patience is not one of my virtues when it comes to modding and like to see results within a few weeks at best and perhaps fine tune over the course of time.
Getting it as good as possible mechanically is the first thing that should be done.
If that doesn't yield good enough results for me I try to obtain a mechanical 'adjustment' that is easy to correct electronically.
This may lead to other mechanical mods than would be obtained by purely mechanical mods though.

Being a (mostly analog) electronics designer makes me wanna use electrical modification much sooner than most other modders I reckon.
I have easy access to equipment and components which also may help in me grabbing electronics to modify the signal.

I think all pirates here are after the same thing.
Improving the sound of their headphones through available means and personal abilities.
By sharing this info others may benefit from these experiments done by others.
The neat part of the pirates here is they ALSO use technical means (measurements) to aid in their search for improvements.
This is why I joined here.

Yes PM-1

Oups... Do you mean they went a bit too far with taming the highs that no eq will wring the stuff back / too muddy to ever resolve like an hd800?

The PM-1 a few of us heard at the micro-meet was the second beta. The frequency response really was rather nice with no audible peaks and perhaps as n3rdling mentioned some treble roll-off. Supposedly, the production version is even more rolled. It depends upon who you speak to. As for the matter of resolution, I would listen to the HD800 with both acoustic mods and maybe even some EQ, so I consider this issue largely unrelated to FR - while acknowledging that a bump in 10kHz does help create the illusion of more "definition". But definition is not resolution.

The major issues I have with the PM-1 were as follows:

• Very closed. I remarked how the PM-1 were subject to certain limitations in that they were closed phones. The small crowd around me laughed and teased me by pointing out that the PM-1 were actually open headphones. The fact that I was convinced they were closed headphones is telling.
• Mushy, slow, muddy bass.
• An overall veil to the sound, especially around the vocal fundamentals.
• As n3rdling said above, resolution more akin to iBuds than to its competitors: Audeze, HFM, etc.

I see no reason to spend over $1k on the PM-1 when the HD600, HD650, HE-500 are superior options

That being said, it is an ortho, so one can mod them. I'd like to get my hands on one for measurement.

a bump in 10kHz does help create the illusion of more "definition".

The perception of such illusion varies from individual-to-individual I think. I'm practically immune to the 10KHz spike in DT 880s for example, presumably because it's coincident with my personal concha gain.

This is probably why headphones with insufficient response in that area sound somewhat dull to me. Based on this I would think the PM-1 would sound utterly unagreeable to me.

I think peaks and troughs outside compensation for ear gain are far less agreeable in general.