This is an HD800 to an 800S mod, made more improved over all past mods, plus secrets learned along the way. Preface: This was to be called HD800 (Wuotan) Mod... too much. Then I just called it the Ult "S" mod. Call it whatever you like. I will post the performance evidence first, then followed by the procedures, and discoveries made alone the way... HD800 to an HD800S mod: FR: notice elevated lower spectum to bass, and gradual elevated upper spectrum, no dips... Previously impossible to have without the 6k ringing.. CSD: 30db down. Notice that all decay is faster than .5ms (!), all way down to 1k.. No 6kringing like stock and even 800S... Clean CSD, unmatched by any HD800 or HD800S elsewhere (in regards to FR & decay). Here is a screenshot of the best fabled never released annax mod: pic At 50db down a slight 1-2ms decay in trebles, (arguably the cleanest ever made) Now here is mine 50db down: (click to expand as looks too big to post large) At a deep 50db down, Fast decay of .05-1ms in WHOLE trebles range! This is proof of no ringing(!) This is unmatced by any modded HD800, or HD800S... ever before... Distortion: Notice that the harmonics below noise floor, And also to see is unique is the horizontal linearity of the harmonics. In this one, the ambient noise was too high, so the white line (THD) reflects that, and I removed the bass as debatable points because of the noise, but it was a gradual incline with the bass. So the Bass measurements were too skewed because of the dam ambient noise so I will try update in future post. One important point to note to make, is that no other HD800 has ever had a linear distortion (no spike) in the trebles range, and also stay below the noise floor... ever..(that I know ).. This is unmatched by any modded HD800, or HD800S. Hear is my Impulse response: First, It should be noted that this impulse, being the HD800, should be viewed already as a notably clean and noise free impulse response.. Small signal wiggles before the main peak, would reveals system distortion, of which there are none here. The main signal is the large first peak. *There is Less negative overshoot than an 800 or 800S. *The lack of a strong second upward spike after the initial transient is very important, and is less than other HD800 or 800S... This is said to indicates a more coherent sound, and superior imaging. *The tighter rise & fall of the lines being tighter to the red line ( in this Mod), compared to stock, is also indicative to cleaner response. All below the 20 mark is already very good, especially if before 500ms. *The smaller signals after the initial up and downward spikes, are the ringing/reflection amplitudes of the enclosure, of which is also better than any HD800 or HD800S. *Suffice to say this Impulse response as a whole, is also unmatched, by any modded HD800, or HD800S. About this mod: There was no mod available, to make an HD800 sound similar, (but better) to an 800S... So this was the goal... As you can see by my performance measure. No other HD800 or HD800S has this level of performance... Add to that, To also have the hallmark Sennheiser trebles and better bass than the 800S... This mod WILL give you the bass, without the added blurry harmonics of the 800S(!). This mod WILL preserve the treble "air" and signature Senn trebles, that other mods either kill off(rug liners & creatology foams) .. This mod NOT intended to replace the neutral "Super Dupont" mod, which flattens and evens out the trebles...In order to also lessen the 6k resonance. This mod CAN be partially applied to FURTHER REDUCE riging in the "Super Dupont" mod.. Essentially making it superior to the fabled never released specs of the annax mod. This is the only mod that eliminates the resonance problem WITHOUT killing, or neutralizing the trebles... This is an all unique mod comprising of nobody else tweaks, liners, etc.. It was a year long project that me and another member @ Olegausa finished about over a year ago, so is about high time it gets revealed. The upgrades revealed here will be up to the user next posts coming soon... EDIT: Some more measurements... Comparisons of this mod to another HD800SD with StephanAudio hardwired: This is a "clarity" tab in REW showing a graph visual representation. This mod is on right side. Next: This is the "distortion" tab in REW showing the red line (2nd harmonic) distortion go up around treble region, which is one indicator of the HD800 treble resonance this mod solves... Notice this mod on right side devoid of such elevated distortion. Next: This is the "Filtered IR" tab in REW. Here we see in numerical value, the "clarity C50 & C80" results. As you can see, the C80 measurement is the one to look at. On a plain or SDR moded HD800, expect to see 19-20 or lower. This mod's "C80 clarity" at 56, is more than double of the original HD800, even with a center driver mod like SDR. I don't expect these numbers to be beaten by any HD800, anywhere... Hopefully someone in future will "carry the torch" and achieve more?