Figured it might be time to post about what I've been doing with the TH900. I've tried about a million things with these, and the pictures I'm going to post are pretty much the best I could get them before I decided to use wood glue to permanently screw the cups in place. Not because they're perfect, but because I had already crossed the line into insanity and needed to preserve my own mental health. The tuning I arrived at was as close to perfect as I could get for my tastes and given these headphone's strengths. No, they'll never have the imaging of some open headphones, and they'll never be dead flat. But for tactility and slam with a fun tuning that still reveals mixing choices and recording differences with ease, I haven't found better. Lets just say this is the headphone that is making my 3 pairs of HE6 sit and collect dust. When I first heard the stock 900s, I was mortified. Sharp lower and upper treble, fucked mids, bass completely separate from the rest of the response. Yuck. I had already heard the X00s and knew the 900s were built in almost the exact same way save for the pads, so I knew there was potential (turns out the X00s have ZERO cup damping stock, whereas the 900s are stuffed with some type of loose acoustic fluff). Anyway, I started my journey many months ago and am now fairly close to calling it quits - I'm just doing pad rolling for the most part now. Along the way I learned a lot of functional knowledge and have a feel for what little tweaks could be made to change things like the degree of the cup effect, the localization and amplitude of the bass boost, the general slope of the response, the degree of the BBC dip, things like that. This headphone is actually a great modding platform for experimentation - fairly easy to take apart (4-8 small screws per cup depending on what you're trying to do), and every change makes a measurable, perceptible difference. I've experimented with over 40 materials in every sensible arrangement - front of driver, magnet assembly, front and back of baffle, cup inside, cup outside, pad mounting ring, pads, headband, the list goes on and on. I've even experimented with some irreversible things too, like tearing off the paper damping on the rear of the driver. You'll see - Cups: Bottom layer - Dynamat-like goop around the outermost portion of the cup perimeter, covered by adhesive felt, rug liner in the deepest flat portion under the cup surrounded by small cuts of dense crafting foam with more adhesive felt. The felt covers around 60% of the bottom of the cup as you can see. This felt doesn't deaden the cup effect in the bass and lower mids, but it does eliminate internal treble reflections and helped to smoothen the treble quite a bit. Second layer - More adhesive felt around the top portion of the cup. Dense foam nubs around screwholes were later removed, but further experimentation here will be done. Circular covering of memory foam taken from the inside of a headphone pad and cut to shape (varies in thickness / sloped). The shallower parts of the foam were covered in fairly densely packed cotton, cut from dental gum swabs. I know this looks like an assload of damping, but the rear portion is still bare wood under the rug liner, and the memory foam actually breathes quite a bit. Basically the rear hole on the driver assembly is the only thing that fires through the whole cup depth, the secondary driver damping fires into the cotton/foam blend. This helps to lessen the degree of the BBC dip (though it's still definitely there), though not kill off too much of the cup effect. Took a LOT of experimentation to get here. Driver/Baffle Rear: Removed all paper damping on driver assembly (kept baffle paper). Micropore'd selectively for symmetrical half covering. Dynamat-like goop applied to top and sides of all non-obstructive parts of the assembly. Plugged baffle port with foam and micropore tape (this fixes the lower mid dip but also traps a lot of energy in the cups, was later removed when I settled on a pair of pads the alleviated the dip without this mod). I've tried stuffing all the driver holes with all sorts of materials but this option gives the most freedom of motion for the driver - once you do this, you have a lot more control over the dynamic presentation because whatever you do with the cups has a much greater effect. I did use foam to plug the open cavity where the cable ran through the baffle. On other pairs this is hot-glued shut at the factory. Even with all my cup damping, you can physically feel mechanical conduction in the cups as the music is playing with the reduced amount of driver damping. Addictive. Pad mounting ring: This ring actually sits in front of the outer portion of the front baffle, so damping here does make a difference. I added dynamat-like goop and also a layer of adhesive felt (not pictured). This covering made the pad mounting mechanism obsolete, so I now use double-stick tape for all of my pads. Exterior: Dense foam applied with about 70% covering. This has MUCH less effect than the same amount of foam applied to the inside, since you're not affecting cup dimensions. But it does help to tighten things up a bit. Could go without this with a different internal scheme. Notice the foam that couples the top of the cup to the headband - this makes it possible to adjust the degree of the cups relative to the ears in a fixed way, which is helpful to maintain a perfect seal and comfort when on the head. It also helps conduct some of the cup resonance to the headband (I can feel the headband gently vibrating with my finger as music is playing) - jury's still out on whether or not this is a perceptible or important difference, but to me, it adds tactility in the bass while also reducing boom. Final FR with zero front damping (aside from stock foam that sits around the driver on the front of the baffle) and AP2000Ti pads (my favorite on these, really a random find, and honestly they are a little too small). I stretched them a bit to fit onto some plastic rings and taped them down, but there's still about 1-2mm of extra space around the pads. Doesn't bother me - looks a little jank, but IDGAF when they sound right to me. EARS and SBAF comp curve - modeled after Marv's - Don't mind the bumps in the bass - just my noisy AC unit. Haven't changed my comp since all the measurements on this thread ( https://www.superbestaudiofriends.o...easurement-dump-zmf-focal-audeze-extras.8087/ ) so you can use that for reference. This graph's got 5dB scales though, hopefully that's easier to read. Happy to post measurements with different scales or pads or damping or whatever. 10dB dip at 3k looks like a lot, I know, but considering the general slope it's probably closer to 3-4dB below what I'd consider my target. Some pads help with this, but bring other issues. I've tried about 20 pairs. If only I could open them up one last time... but I won't go there. EARS isn't great with CSDs or I'd post those too. Need to figure out how to do accurate distortion measurements... EDIT - A couple runner-up pad combos (both with 2-ply TP front filter, which isn't needed with the AP2kTi pads, and treble-tolerant people like @brencho could probably do without TP on these too). I'm super sensitive to any amount of treble accentuation, which is why I never let the FR in the highs supersede amplitude at 1k. Same comp as above, but different dB scales on the Y-axis. Can fix this later. Stock TH900 pads - Brainwavz XL Lambskin - Modded HD6XX (posted about in the 650 thread - kind of like KISS mod) Going forward, I have a pair of X00's I'm going to keep messing with indefinitely. Feel free to ask questions like 'what happens if...' - chances are I've already tried it, or if not, I'll do it and provide measurements here. There are at least a few dozen things I've tried that I haven't mentioned above. This is the best I've been able to do so far. Hopefully I can get some more impressions soon!