Speaking only for myself:
The dust cover is very thin and loosely woven. I removed it on one set of mods and heard no change. Then, again, others have. I hear nothing above 15k Hz. Maybe removing the dust cover opens things up above 15k.
The stock white driver felt is part of the design. Remove it or work with it. I've done both. I prefer to keep it there and work with it. That said, IF you end up removing, try to carefully remove it with acetone and X-acto knife so you can re-apply with rubber cement if you want to go back to stock. I have done this twice. With your preference for more treble, and if you remove the white driver material, I think you might be pleasantly surprised what you hear with Transpore tape over naked drivers. To ME, 1 layer has too much bass, 1.5 layers is the sweet spot, and 2 layers further reduces bass quantity and further enhances treble sparkle.
You could try a reflex dot on the center grid overlaying the white material. Be careful if you remove it. I made a little tear in the white material once. I used a furniture bumper from the same pack I had used before and removed a dozen times without incident. You might want to press the reflex dot adhesive to a shirt sleeve or other material to remove some of the adhesive before sticking it on the grid.
You could try:
1. reducing the amount of plasticine and/or acoustic foam to free up more cup volume.
2. a different quantity, density, and type of filler vs no filler in the cups.
3. covering some of the bass port vents.
4. "limp" vs stiffened felt over the white driver material in various configurations and/or layers
5. roll up a Kleenex tissue to make a paper "rope" and place under back half of pads; try smaller vs larger (length and diameter). This is the easiest mod and can make a big difference in sound quality. I previously gave my opinion that I heard no difference between stock pads and 840 pads.
Good luck and report back what you find.
Disclaimer: I want to just stress that these are great sounding headphones. I'm mentioning only the flaws in this post
About the drivers, I was actually getting close to coming to the same conclusions the other night. I've still been trying to track down the source of this 1k resonance that's been plaguing my build. I removed the cups, and pressed the baffle and pad against each ear so that I was essentially listening to a completely open headphone (it wasn't comfortable - I had to hold my head right against the desk!). It essentially sounded the same, with the same problems as when I had the cups on. Good news there is that the foam, mass damping, and cotton wool I had in the cups is doing its job, and essentially providing little by the way of reflection, which goes some way to explain the quite open sound I have. The bad news is, the 1k resonance was still there, the slight muddiness and congestion was still there, and the lack of treble extension was still there. It's not a great test, because you could easily argue that the driver isn't supposed to work in an open design, but since the flaws are essentially the same with and without the cup, I think it's fair to hypothesise that it is the driver / housing / baffle for the moment.
Now, a couple of things about my build - I've still got the stock white fabric on the back of the driver, and the stock black fabric on the ear-side. I'm slightly nervous about removing them, as it would take my build over the line, and into irreversible territory, and I'm not sure how easy it is to get equivalent fabrics in my area. I imagine removing that black ear-side felt will open up the sound somewhat?
Am I the only person noticing these 'flaws' (or characteristics, if you will) of the sound? If that's the case, I probably need to change my build. Or, do we think it might be inherent in the design of the driver / housing? Or, as another option, is it an issue with the pads (I'm still using stock, though I believe BMF stated they sound the same as 840, a few pages back). Or, is it simply the headphones I'm comparing to? You can see from my signature that I tend to prefer fast / analytical / sparkly sound signatures. I love the lush richness of my T50rps midrange, but do I have to sacrifice that to obtain the other qualities I enjoy?
Edited by bluemonkeyflyer - 11/2/11 at 9:55am