And... this is it. To me, this is the ultimate. Here's the non-3-step version for those who wanna go overboard: Materials needed: EPE foam sheet (0.5mm): https://www.aliexpress.com/item/0-5...-Laser-Warp-Shipping-Pre-cut/32803182359.html Shelf-liner: https://www.amazon.com/dp/B002AS9NB2/ Medical face mask: https://www.amazon.com/Commercial-Surgical-Disposable-Registered-Approved/dp/B01DEMPDJ8/ Bird cage cover: https://www.amazon.com/Sheer-Guard-Bird-Cage-Skirt/dp/B00856MOXW/ The following stuffs are optional and should only be purchased if you want to fine-tune sound/treble: Earphone steel mesh: (you want the 5mm ones) https://www.aliexpress.com/item/Dus...sh-filter-gum-never-rust-belt/1975223569.html Dynamat: https://www.amazon.com/Dynamat-10415-Self-Adhesive-Deadener-Speaker/dp/B00020CATC/ Copper tape: https://www.amazon.com/gp/product/B071LPC99Y/ Sennheiser's official grills for HD600: https://www.audiosanctuary.co.uk/sennheiser-replacement-grille-for-hd600-headphones-each..html (alternatively, just call Sennheiser up and tell them you're looking to purchase part # 092815) Steps: 1. Take out the foam in the rear of the drivers. 2. Cut the EPE foam sheet, shelf-liner, and the perforated layer of medical face mask to this exact shape: (note the direction of the shelf-liner) 3. Cut the bird cage cover to the shape of the stock foam piece, or at least barely enough to cover the elliptical driver thing in the middle. 4. Avengers assemble! Medical face mask on the bottom, then foam sheet, then shelf-liner on top, use the bird cage cover to keep them in place and just snap the ear pad on. Note: when snapping it on, the ear pad should stretch the bird cage cover out, that's normal. 5. Done. Do #6 if you want to fine-tune treble/speed/whatever. 6. Replace stock grilles with new grilles from HD600, then put dynamat and copper tape in the following places: Note: the following 3 photos are specific to the "right" driver. Please "mirror" them (in other words, flip the images) for the left side. It's gotta be symmetrical. Conclusion: I'm crazy. And this is just to replace the stock foam pieces for the most part. It may sound better, it may sound worse, I dunno. You decide. No express guarantee on sound improvement, but at least your HD580 won't have foam in the front and rear anymore. Also, I use Bottlehead Crack w/ Speedball and a black Schiit Jotunheim to tune this, but it probably won't make a difference (or will it?). Oh, and all of the above *may* also work with HD600/650. I dunno. You're gonna have to try and let us know. For 3-step mod: (kinda have to use a bit of your imagination here, but no need to go overboard with everything else IMO) 1. Remove foam thing in the rear of the driver 2. Use EPE foam sheet with 2mm thickness (Aliexpress will have some, I think, just look around) instead of the 0.5mm thickness as above, no need for shelf liner or medical face mask. Still need bird cage cover. Vary foam sheet thickness if you want more/less bass. 3. Replace grilles.