Just joined to share my modding tale with you.
I usually use Sennheiser HD 598s, however wanted an extra / cheaper closed-back headphone so decided to try the HD 419 for comfort reasons (felt instead of pleather, over ear etc).
Anyway, Sennheiser sell the 419 for the non-audiophile bass crowd, as an alternative to Beats etc.
However, that interested me as Senns are often too weak on the bass to my ears. I'm no bass head and like lots of genres, but whatever music, bass is of course an important mixture and I even find the kick drum on my 598s lacking oomph.
So, I burned my 419s in for about 60 hours, and sat and had a listen.
They sounded slow, distorted, snare had no snap, highs and crashes sounded like they were under a blanket in another room.
The bass from 60 - 120 was strong, but not very smooth. Not much sub to speak of.
So, I read through this thread on here http://www.head-fi.org/t/441191/new-sennheiser-hd-448/90 for modding the 448.
Then, I got to work.
I followed the above link directions (419 identical inside) and removed covers, screws, and then, slid the drivers out.
THIS IS THE DIFFERENT BIT TO THE LINK.
If you remove the the tape from all three holes on the back of the drivers, it would be way to bassy, and reverberate around the closed-back driver casing. BUT, of course the more air a speaker can move, the more quickly it can react and therefore sound much better.
So, on the casing side, I cut an eliptical shape around 3" long by 2" wide from a fairly thin but soft towel.
I then used double-sided sticky stuff that was thick and foamy (the type from auto stores for sticking the badges on cars). I chopped 4 pieces for each headphone side, to stick around the thin towel. Then, I put the towel into the headphone casing, sticking it down inside the eliptical gap in the casing (where the driver sits when re-assembled).
I then removed the tape from the back of the driver, so all 3 holes are exposed and clear to breathe.
When re-assembled, the towel stops the reverberation, whilst the sticky foam car tape helps remove resonance. But still allowing the driver to breathe through all 3 holes.
Reassambled then listened through some test tunes....
These things sound amazing!! Better than my 598s, far more exciting.
They now have lush highs, massive bass without boom or resonance (really smooth - rock kick drum sounds live!), it has increased depth/spacial perception, MASSIVE improvement in detail (because they are reacting far faster), the snap on the snare is clear but not harsh (even with the most ridiculous bass at the same time), vocals are much clearer.
All wrapped in a really warm live sound. And without the Sennheiser weak bass of even their expensive models. Awesome!
Seriously, try it!