I got a second hand HD800 pair for almost a week now, it completed turn my mod M70x sound metallic and harshness
. If you like the sound signature of M70x, IMO, you should audition HD800 once if you can. The HD800 sound sooooo lively and beautiful
However, HD800 is an open can so it leak sound alot, I can't use it at work
so use HD800 as reference to mod M70x (i also have Hifiman HE 560): reduce metallic and harshness, improve bass.
1. Remove yellow foams behind drivers and black rubbers (cover vent hole?) ==> slightly improve bass
2. Use a thin
Closed cell polyethylene foam sheet, cut a hole in center. Use double side
adhesive tap (as much as possible on the polly cell foam sheet) and stick it to the housing as picture below ==> this will help seal most of unwanted leak air for bass improvement & help damping the back wave
Note: if you use the stock pad, you should trim the poly cell foam fit with the gray foam of the housing. I use the Audeze leather pads, it cover all the housing surface.
3. At this stage, the M70x sound boxy ==> you have to poke a hole or more as your bass taste (red circle, you should see a line of wholes on the housing frame when remove the yellow foam). The size of the hole about 1mm (i used toothpick)
Please note the the driver is angled, so half size will very close to the earpad and other half has some spaces ==> poke hole in the half has spaces.
This simple mod (and reversed able) will significant improve bass performance, slightly reduce metallic and harshness sound ==> make your M70x more enjoyable.
If you think M70x lack of bass impact (not bloated), think it again with this mod