The older you go in the Circumaural Stax, the brighter they were. Stax have always preferred "thin and bright" tonality, which is not at all accurate, but certainly attractive if you like that kind of sound. I lived with a pair of SR-3 that I used on location for mixing for many years so you can certainly get used to or adjust to that sound, but if possible, in my not so humble opinion, you should Equalize every headphone you encounter to help linearize it.
I much prefer "natural" sound to over bright so if (as someone just said in this thread) the 007 Mk2 is an "outlier" I would say, bravo, because it's warmer and more accurate than a lot of the other Stax. I don't know what Stax were thinking making the more expensive 009 so much brighter than the more accurate 007.
I have a pair of pro diaphragms that were originally in a Lambda, now they are inside of an SR-5 case that I had. Someone (I forget who, sorry) put the pro diaphragms in my SR-5 case for me. Like so many of the older Stax phones, those sound very bright and thin. They are also about 6-10 dB hotter (more sensitive) than any current circumaural stax. But surprisingly, after EQ, that old pro model that's in an SR-5 case sounds very respectable! It can take a bass boost without overload --- and I'm quite pleased with what these old phones can do. So, the ingredients you need are: A high headroom Stat amplifier, and a great DAC with EQ (like the RME I mentioned). Feel free to write me for my EQ settings, it will get you in the ball park and you can tweak to your taste from there.
Cheers Bob, I don't forget, since I don't have that many friends
Those were mine originally, and those drivers were transplanted from am SR-Gamma Pro, since as you said Lambdas are a different shape.
Kind of funny that it's just been brought up:
https://www.head-fi.org/threads/stax-sr-x1-new-entry-model.971680/post-18072756
As I've just tested a new prototype of an SR-5 Pro conversion done by another person in a new way.
Does remind me of that pair I sold to you - but I don't evaluate it the same way.
On the Carbon amplifier, I find it to be surprisingly
dark, darker than an SR-007 Mk1, because of the limitations regarding the smaller, much more damped housing means the treble response isn't as capable.
And if I were to apply any EQ to it, I would aim do the exact opposite, e.g. brighten it up to restore clarity.
https://www.dropbox.com/s/vzfx5kw28r64gac/Stax SR-5 Gold.pdf?e=1&dl=0
This is the SR-5NB used with a Stax amplifier which is of course not identical to using a Pro version on a Carbon, both of which change the sound notably.
The SR-5 Pro a headphone where I'm not inclined to push the volume too high on the Carbon - bass actually gets overpowering, which is rare to see on any Stax.
I found it to be quite an addictive for classic rock, where an SR-007 might be "too refined, overly smooth".
For me, there is also a very clear distinction between an
even/smooth response and
balanced tonality (e.g. not bright or dark etc. but this is actually quite hard to judge depending on which colorations weigh in more on that, so quite a personal judgement)
And while I may not achieve the same balance as with a speaker, I might not actually aim for that.
As high-end headphones do have other attributes against speakers, that may actually worth putting more emphasis on.
So yes, I'd say that while this may be an oversimplification, but an SR-Omega and SR-007 Mk1 are in general brighter than an SR-007 Mk2.
But I
would rather have that than an SR-007 Mk2, which might be more balanced on a brightness/darkness scale.
But - and there is a big but - it is also filled with even more dips and bumps in the frequency response that
bother me more, and no EQ is going to bring that up to the same level of transparency. I tried suited EQ curves for both Mk1 and Mk2 versions so in essence they are corrected to the same target (provided that these curved matches the actual samples I testead) and yet: the Mk1 still sounded
better to my ears for the most part. (considerably smoother, more open soundfield, while Mk2 has slightly better bass impact)
I also extensively tested the RME DAC as well as a Prism Lyra 2, the latter particularly stood out like an exceptional D/A converter on its own, technically speaking.
But - and a big but again - I also found neither to be very well suited to Stax headphones in general: sound became brighter, "more digital", unpleasant to my ears, while the Lavry DA11 does take a bit of a hit with regards to clarity, but it also seems to sound more natural, less bothersome, without injecting a heavy signature of its own.
So one day maybe, I'd like something similar to that. Technically more capable, but without injecting changes on what I've already set up (if I could achieve even more fullness without changing any other attributes, I would certainly take that as I could lower my listening level)
Maybe a Bricasti M1 Series II or something could be worthwhile for an otherwise fairly sophisticated setup to make it "more complete" - unfortunately very expensive...