Apologies in advance for the lack of photos or sound clips...
I found a spare sheets of Nexus acoustic damping material today and since it is fairly heavy I decided to stick some inside my Cherry G80-3000. There are a lot of voids within the case - the whole area of the case has been 5mm and 10mm underneath the PCB to the back of the case. It has little ribs which support the PCB. It is between these ribs that I've stuck the damping material (and in the area at the top of the board which seems kind of redundant and a waste of space).
The whole process took a couple of hours but I'm impressed with the outcome. It is noticeably heavier. It's crazy - the build quality is no better than it was before, but holding it in your hands it feels like a more expensive product simply due to the weight of it.
The keys sound a little different - maybe slightly lower pitched than they were before. I can't explain it, but having been using the unmodified G80-3000 for months it does sound like a different keyboard, and I don't think it's placebo effect. The sound of the keys returning has the most noticeable different, but the bottoming out sound is different too but to a lesser extent. Of course, the switches still ring faintly and the clicks from the switches sound the same. Overall, I prefer this new sound.
