The Hd 438 is a decent can with 1 major flaw. If your bass is set too high, the earpad material will vibrate violently and tickle your face and your ears to the point of just not wanting to use them anymore or totally removing the bass via EQ. On my sansa fuze, unamped, with the bass set to about 10%, thats barely anything at all, the tickle factor was pretty significant.
The simple tape mod:
So, I decided to try something. I couldnt get the earpads off, it gave me a lot of trouble. I called sennheiser to get some support as to how to safely take them off because it was requiring way too much force to pull off and i didnt want to break it. So, I was told to pinch one end and pull. It popped right out easily, thankfully.
I placed a simple rolled piece of tape on the top and bottom of both openings making sure to not cover the holes. Slipped the pads back on.
Oh my goodness the rattling and tickle is almost totally gone. Perhaps later I would replace the tape with felt or something else that will hold more of the back of the earpad directly onto the plastic driver housing. This is not just a bass improvement, its an overall sound quality improvement. That 1/4 inch between your ear and the opening itself ruined the sound quality and produced significant rattle factor. This simple mod almost totally eliminated it and will improve if i add more stick material to it and make sure as much of the back side of the pad is actually stuck to the top of the inside of the cup.
The sound quality is actually noticeably increased. Test for yourself and see if you have a pair. This mod doesnt void your warranty and can be removed with ease so long as you dont use glue. Im stunned actually. Im very happy with the results and this needed to be done, i was really stressing out over that damn rattling. The backside of the earpads created a small screen effect to the music and after i smoothed it all out, it sounds a little more clear. This can went from bass light to bass "pretty good"
this mod should be a requirement for this set. I can turn my bass EQ all the way up and there is no sign of rattling or tickling of my ear and face. Awesome.