other than strange matching at like 2k? ish? that looks pretty goshing good.
any idea if the K551 sounds the same and has less unit-unit variance? that would make these an OK rec I think?
as I assuuuume the K550 is discontinued because of K551?

Thanks for measuring these, purrin.  I do not plug them into amps, just enjoy them occasionally out of an iDevice.  Two other pairs of K550 that I have heard could easily get annoying for us with that weird peak.  These don't have the same issue the other two did and I like the sound sig.  Very interesting to see the Left side ringing.  Will have to see later if I can pick that out.  (Glad it's on the left rather than the right as I probably attenuate HF in my left ear a bit.)

I have found that the K550 works better from 120 ohms output impedance. I know that many think that the effect is very subtle but it does seem more 'natural' in the treble region when the output impedance is higher.

At near zero, I find it a little on the thin, edgy side but put in some resistance and it takes that sharp edge down a tad.

Astralstorm, with those three 'versions' of sound you were getting, were they all produced recently or were any of them the first batch? There are always stories about headphones being quietly modded or whatever, but to have three versions of the same headphone seems to show up poor quality control if they were made around the same time.

Especially seeing the ringing that Purrin has seen in the left cup but not the right.

Samples I've heard:

• HeadRoom: Absolutely horrible. Will destroy your hearing.
• RD #1: Only heard the modded version, which was still horrible. I assume when unmodded - as horrible as the HeadRoom K550.
• RD #2: Slightly better than the above, but still horrible.
• CT: Pretty good.

Yes, it's very weird. Looks like the same problem that the Beyer DT1350 seems to have. ie: quality control. Or else, it has been quietly 'developing' as a headphone. (I doubt that though since once they're designed, the companies tend to leave well alone unless there's a real problem)

Mine is one of the first out in the UK. Tomorrow, I'll have a new one so I'll compare the two.

I have my amp set at 100 ohms out and that seems to calm the sting in the top. (It's a valve amp as well)  It still has its lively top end, but not as 'stabbing'.  No bloom on mens' voices and yet it shows some really very deep bass on some recordings too. (So no hump in the mid bass to colour mens' voices)

I guess the K550 is on its way out since it's now being sold quite cheap over here in the UK but if they are so variable, you're not guaranteed a good one.

Mine doesn't seem bad in spite of being one of the first over here.

I tend to have to wear it quite 'high slung' in order to ensure a good seal as well. Higher than my other headphones anyway - so that the bottom of my earlobes are just touching the inside of the pads - I find I get a robust bass in that position.

I wonder whether the CT one is a more recently made headphone?