I may redo this one. I wonder if I had something vibrating or mounted the wrong way.

Wait, did we just use our ears and brain to catch an objective measurement artifact?  O-M-G!!  Hell just froze over.

Consider this post an update.

Today Solderdude and I met up for measurements. I brought the K400, two K500s, the K181, the DT250-250 and the SHP9000.

All of the headphones are measured and we found some interesting results. In short, if your K500 or K501 sounds too rolled off on the frequency range extremes, add the K601 ear pads.

For more information check with Solderdude.

Many people outright liked or detested the K701. It was AKG's top of the line controversial headphone years ago.

The K400 just sounds smooth without a hint of glare.

It sounds quite good. Bass is tight but lacks ‘body’. There is no bass extension at all and sounds ‘lean’ compared to other headphones. With some music this isn’t very obvious but with well made recordings the lack of bass extension is obvious. Tonal balance is very good, instruments and voices sound very convincing. The treble peak is there and it makes the K400 sound detailed, yet lacking finesse. Compared to better headphones the treble and fast instruments have some ‘spike’ to it. It accentuates attacks with some instruments in a slightly artificial way.



Yes, those spikes are really there but aren't as obvious in the sound as one might expect.
[edit]
NOTE: the spikes that are measured here MAY have been caused by the fact that it was tested at 95dB SPL, which may have been a bit too much for it.
This headphone does start to distort at higher listening levels much sooner than most other headphones.
While it did have an edge to it at normal listening levels (around 80dBA) it certainly did not sound as bad as the measurements would suggest.

The CSD shows the 7kHz and 13kHz peaks to be the result of resonances, the 7kHz one quite severe even. The peak in FR and ringing may explain the ‘edge’ in the treble and the somewhat artificial sound on cymbals etc. Below 5kHz everything seems quite good. left, right



The positives are a neutral sound, not muddy, and good comfort.
Negatives are the lack of body (bass extension) and the slightly ‘edgy’ treble.