A few weeks ago I found a pair of HD500s in a box as I was looking for something else. I'm pretty sure they were a gift from about 10 years ago that were just forgotten about. After I gave them a listen I realized why: they're incredibly dark. With considerable eq adjustment I could get them to sound pretty decent but I was looking for more. I came across this old article on HeadWize about using some metal cutouts in the plastic baffles to increase clarity. The result wasn't all that elegant -- I wanted to get more of an HD600/650 kind of look. First, I popped off the baffles and cut out the center, so that I was left with an oval ring. I bought some black metal 6.5" speaker grills on ebay and traced onto them the outline of the baffles and made cutouts. I rounded the edges so there was a bit more bonding surface area, and epoxied them to the baffle sidewalls. Finished with a couple coats of flat black (the plastic baffles were originally grey). The area that was epoxied came out a bit lumpy which doesn't look that great up close, but from a couple feet you can't even see it. I like 'em, it dramatically opened up the sound, and they look a thousand times better than the grey eggs they started off as, IMO. That "bionetic" design might have produced some pretty ugly shells, but they're SO comfortable.
