I've poked, adjusted, cut, soldered, nipped, tucked, and otherwise tried a plethora of modifications to my HD 555's. I think I've finally reached the point of diminishing returns. When I first started down this dark path, it was easy to “pick apart” the sound, isolate things that didn’t sound quite right or even perfect to me with some of the previous mods. I've finaly reached the point where I just really can’t find anything I don’t like about what I’m hearing. My little "sow's ear" HD 555 has turned into quite the "Whole Hog." Let me back up just a minute. I ended up altering my original mod list quite a bit, focusing on the headphones themselves. It really was rather addicting making incremental changes and noting the differences in sound. Part of the addiction has been the joy of rediscovering my music collection--hearing more and more of the artist's intent. I'm listening to Dave Grusin's "Migration" as I write this--albeit somewhat haltingly, because the music keeps demanding my attention. So, to cut to the chase, here's my Sennheiser HD 555 mods--the good, the bad, and the ugly. I'll try and refrain from posting my whole headphone journal here, instead just excerpting the more descriptive and revealing parts where they may be helpful. You'll note that the last mods were done fairly close together--this was on purpose. As I've heard how much of a difference burn-in makes on these cans, I didn't want that to be too much of a variable factor. So I ended up "dropping the needle" a lot through these mods, listening to similar familiar passages over again, trying to evaluate the differences as objectively as possible. I expect some will find my impressions not incredibly objective, but hey, they're only my impressions, not the Gospel. The mods: 1.) 555->595 Mod The first obviously simple mod was removing the foam "surround sound" inserts from the inside of the headphone capsule. This is arguably the only major difference between the 555 and the 595. On my Prokofieff Sym. No.1, what I noticed initially is more "immediacy." As if I moved from the front row to standing right by the conductor. I could swear the bassoon moved a foot or two stage left, perspective-wise. In this recording it seems I could hear the hall more than I remember hearing before. The sibilance is noticibly reduced, which is a blessing on all those high string/woodwind fortzando hits in the first and last movements. On Beethoven's 9th (Chicago Symphony, Solti, London), I just listened to the first movement. This an older, darker recording, and it was still dark--but really much more enjoyable. Again, everything seems more "forward." Hearing a lot more of the hair against the bow from the double basses. While I noticed some improvement in bass definition on the Prokofieff, I noticed a much greater difference here. Actually noticing some key noise from the woodwinds--which I hadn't really noticed before. Switching to something completely different, I cued up Dave and Don Grusin's "Sticks and Stones." This is a funky electronic jazz keyboard romp with a lot of digital drums and synth work. On the first track, "Pico Pico," there's a surprise--there's a reverb effect on the drums that again, I hadn't noticed before the mod. Seems to me this speaks to the negative effect the "surround sound" inserts have on transparency. Listening to the next couple tracks, bass is indeed leaner, and more detailed. On track 2, "Pico Pica," there's some inside percussion parts, timbale and closed high-hat syncopations, that are a lot clearer than they were before. 2.) Soundstage Mod At 120 hours, I finally got the gumption to do the “soundstage” mod.–removing the interior grilles from the headphone frame. I did not add foam (i.e. the hcw mod.) yet. I wanted to be able to distinguish the merits of each mod separately. The effects were quite positive: Prokofief “Classical” Symphony - Oddly enough, the bass, of all things, seems tighter (I really didn't expect this). Seems to be more accuracy–not necessarily breadth, in the soundstage–especially listening to the violins. Dave and Don Grusin - “Sticks and Stones” – On "God Heaven," a piano diet, I can now place the two pianos separately in space - they sound like they’re “nested” in classic piano duet fashion, with the “house-right” piano sounding closer as well (didn’t hear this so clearly before). Makes the duet that much more fun to listen to, since you can hear how the brothers are interacting. 3.) HCW "Foam" Mod. 126 Hours - After numerous (failed) experiments using an old army surplus wool blanket, I cut up an old air mattress (the old “self-expanding” foam style), and used the foam from it to do a “beefed up” version of the hcw mod. Basically I cut an entire foam baffle for the interior of the capsule, leaving just a small opening the size of the magnet right behind the driver to allow the driver to “breathe.” I later increased this opening to the size of the driver. The results were quite positive. Overall, the bass is somewhat more pronounced, but the tonality seems well-balanced, perhaps even flatter than stock. Beethoven Symphony No. 9, 2nd movement - Woodwinds really come out of the middle of the texture well–and well-placed. The balance is very nice between all the sections of the orchestra. It’s a joy to listen to the winds in these passages. The recording no longer sounds as dark and murky as it did in previous listenings. The “character” of all the instruments sounds accurate tonally but also inherently warm and musical. Prokofief “Classical” Symphony - String sections seem much more like sections–I can hear individual instruments in the section stretching across the stage. 4.) Mogami 3106 Recable At 131 hours, I recabled (double-entry) with 10' of Mogami 3106. Rippingtons–“Live from L.A.”--Tonality has changed...Kim Stone’s bass riffs have seriously greater impact–but it seems *both* the highs and lows in the bass are coming out. Beethoven Sym. No. 9 - Movement 4–Bass has much more weight and deeper extension. Still, the parts seem well-balanced. At the end of the Bass recitative, I can actually hear and feel the weight of the bassoon on the last woodwind “hit.” Enya’s Watermark. “On Your Shore”....Enya’s voice is still warm, but clearer. Consonants come out better. Rhythmic synth. notes in "Oronoco Flow" have more impact. Piano comes out of the orchestration more. The celtic drums in "Storms in Africa II" are both clearer and also have more impact on the low end. It’s almost as if the thicker cable makes it “easier” for my old NAD Preamp to drive these phones. The last hit on this track has struck me as anemic earlier in this experiment–it’s certainly not anymore! 5.) "Felt" Mod (Don't do this!) At 134 hours, I lined the inside of the grilles with felt. Not happy with the "raw" look of the HCW mod. (remember I used yellow foam for this...yuck!), I intended this as a mostly “cosmetic” mod. It turned out to be generally detrimental though—lead voices seeming lost and distant. Enya’s voice, the sax on a lot of the Rippington’s tracks--they slide into the background. Woodwinds in a lot of the classical selections likewise recede into the background as well. At 135 hours, I yanked the felt from the inside of the cups, leaving just the foam from the previous mod. Whew! The mids are back. 6.) "Polarfleece" Mod. Did a version of the foam mod. + Felt–only with polarfleece, leaving a hole the size of the driver. Also removed the nylon protective screens from the insides. Prokofiev V - Some of the loud sections in Movement I are actually giving me goosebumps. You can hear so many textures at once–you really start to get a sense of how much of an orchestration Genius Prokofiev was. Tchaikovsky Violin Concerto No. 1 - No other way to say it, Ruggeriero Ricci’s playing, and the whole orchestra, for that matter, sounds more lively and energetic. In Mvmt. 1, there’s a whole lot of broad dynamic phrasing between 6:35 to 7:11 that was never really that evident before. Now the louds and softs are much more highly contrasted. Beethoven 9–On sforzando orchestral hits, bass strings rattle and the bassoon positively growls-what fun! Basses have body and weight even in soft passages. I remember my first impressions of this recording on this setup was that it was rather dark, and even a bit “muddy” sounding. It’s turned out to be a well-balanced, energetic, and exciting listen! So, there you have it. I've ended up with a pair of "budget" cans that are absolutely enjoyable to listen to. I'm actually having a hard time thinking if or how the next phase is going to be able to sound any better, but I guess I'll never know until I try it.