I really enjoyed reading through this thread and would like to share my experience, as a addition to what has already been mentioned.
Amping is important
The headphones are powered by a Little Dot MK II in my setup, which is equipped with matched NOS Mullard M8161 / 6N6-T. This is an OTL tube amplifier, which delivers 300 mv at 600 ohms and therefore provides enough power. Especially high impedances benefit from a lot of output voltage as in the case of tubes. The AKG K240 also sounds good on powerful transistors, but a bit sharp and aggressive on higher volumes.
But with my stereo amplifiers the sound remains far below its potential - with a Quad Vena I (headphone output is supplied via the speaker amplifier), Sharp Optonica SM3636, Onkyo TX2500, HK PM645, JVC RX808 - everything sounds mediocre to poor.
Modifications
Equalizing
Increase the low bass with a Peaking-Filter around 45 to 70 Hz slowly about 6 db at 45 Hz (Q-factor 1.7), cut everything below 40 Hz with a Lowshelf-Filter, set the "belly" between 100 and 200 Hz to -4 db (Q-factor 0.4) with a Peaking-Filter. The bass response is sensational, deep and punchy and still very natural, immediately makes it a more modern headphone.
Foam replaced by felt
The original foam has disintegrated. It is impossible for this foam to have any absorption effect, it is much too thin (7 mm) and open pored for that. It is all about the hinge not coming against the plastic when wearing it, because without the foam you have extreme rattling in the bass. I ran it without the foam and nothing was different in terms of sound. A thin 3 mm foam disc was completely sufficient here that also no dust gets in. I covered all the plastic surfaces, especially in the outer ring, with 3 mm felt so that the high frequencies can't "break" so easily on the plastic and create unwanted resonances.
Ear pads swap
Because many here report about the Brainwavz Earpads, I report about Dekoni Audio and Beyerdynamic Pads.
Original ear pads (+++)
- Sounds the best
- Low bass reasonably present, not particularly deep, but punchy
- Timbre is sensational
- Wearing comfort I found very comfortable, even over hours
Dekoni Elite Hybrid (++)
- The sound has not changed much
- Low bass is raised, but to a pleasant level
- Size of the "stage" remains almost the same
- Very slight worsening of the "timbre"
- Voices takes place slightly more in the head (center imaging)
- Wearing comfort is sensational
Dekoni Choice Leather (-)
- Sound is degraded
- Low bass is raised strongly, but spongy and thickened up
- The entire stage becomes much smaller, the sound is no longer spatial, especially the reverberation is drowned out
- Frequency response shifts, peaks in the high frequency range become more prominent
- Wearing comfort is okay, the pressure is quite "concentrated" on one spot
Beyerdynamic EDT-990 V & EDT-770 V (--)
- Sound is degraded
- Low bass is erased, no longer present
- High frequency range is more prominent, unbearable to listen to
- Wearing comfort is okay