DIY Modification for the Sennheiser HD 800: "The Anaxilus Mod" Page 2

Not having all the cool software that Arnaud has to predict how the mods might work, I decided to take the empirical approach and simply try a lot of different materials and shapes and then measure them. The materials I tried were:

  • Closed cell polyethylene foam - this is the material sometimes used like bubble-wrap to protect things during shipment. It's a rather springy closed-cell foam. Buddy and Head-Fi member JohnJen built and sent me the 5mm part, which is what really got me going on doing this article and the HD 800 review now. Thanks, JJ.
  • Creatology craft foam - this material is available at craft stores (I went to Michaels). It comes in two thicknesses (2mm and 10m), multiple colors, and has a peal-off adhesive backing.
  • Creatology foam with a polyester felt layer on top - the felt material is also available in small sheets at craft and fabric stores.
The geometric variables were the width and thickness of the ring around the driver. The "wide" rings extended out to touch the stainless steel mesh of the earpiece; the narrow rings were wide enough only to cover the surface of the ring. The thickness varied depending on the material used.

The picture above shows some of the mods I tried. There were more parts tested, but a number of the thinner and more fragile parts were destroyed upon removal from the headphones.

I first compared the frequency response of the various parts. (The FR graphs are all aligned to be the same level at 200Hz.) I'm just guessing here, but this is what I think I'm seeing. As the part takes up more volumetric space in the headphones (the thick ones, and to a lesser degree, the wide ones) you get an increase in level between 300Hz and 5kHz. As the part gets wider, the tendancy to dip at 3kHz increases. As the part provides a less reflective surface, the peak at 6.5kHz lessens. (Clicking on the frequency response plots below will link you to a .pdf that you can zoom in on the curves for a closer look.)

Sennheiser_HD800mod_graph_CompareLeft Sennheiser_HD800mod_graph_CompareRight

Initially, I thought I was going to hear some reduction in treble energy relative to the lows, but that's not the way I heard things. I did notice as I listened to the various mod's mild colorations that are hard to describe. Sometimes a "heaviness" with the bigger parts; sometimes just a sense that the sound was less transparent; but it was pretty clear to my ears that the Foam Felt Narrow part got in the way least. It seemed the most pleasant and least biting.

Looking at the frequency response comparison of that particular part (it's the heavy red line in the plots), the main differences I can observe are: a clear lessening of the peak at 6.5kHz; a slight level increase between 500Hz and 3kHz; a very slight increase in bass; and possibly slightly smoother and lower in level than average response above 10kHz.

Somehow, that didn't seem to have a lot of meaning relative to what I was hearing, so I decided to have hard look at the square wave response.

300Hz Square Wave Response
Sennheiser_HD800mod_graph_SquareWavesTo the right are all the left channel square wave response plots of the stock and modified headphones. Let's work our way down the list. Comparing the stock headphone with the stock headphone without the liner, you can see that the amount of noise significantly increases without the liner. I think the noise seen is some ringing at 6.5kHz, which I think is the culprit that tends to make the HD 800 sound piercing. The half wavelength of sound at 6.5kHz is about one inch, which is about the distance between the ring around the driver and the side of your head. I suspect the peak we see at 6.5kHz is the primary resonant mode between the driver and ear/side of the head.

The next square wave is the 2mm Creatology Wide part. Here we see a reduction in noise from the stock headphone without the liner, but it's not quite as quiet as the stock headphone with liner. I'm not sure why that is, except to say that the elasticity of the foam might be storing a little energy (wild speculation on my part). Also note the slight tip downward of the top of the square wave. This typically indicates a change in the relationship between mids and highs. Tipped in this direction tends to indicate a thinner sound; tipped the other way tends to indicate a warmer, punchy sound. Don't know if I really heard it that way, except to say that this part did seem a little colored to me relative to the narrower version we'll see next.

The 2mm Creatology Narrow seemed a bit better sounding than the Wide to my ears, and it did seem to clear up the bite of the HD 800 some. I liked this one, but decided that more exploring would still be worthwhile.

I next tried the much thicker 10mm Creatology foam. Because it was so thick I tapered the sides figuring it might make a tube around the driver that would color the sound too much. This part did seem obviously colored to me in that it seemed brighter and more piercing. A hard look at the frequency response comparison will reveal this part showed large increases in energy between 500Hz and 5kHz, and a significantly bigger peak 6.5kHz. The square wave has quite a bit more noise as well.

The 10mm Closed Cell Poly part was similar in shape to the previous part, but sounded even more colored, though not quite in the same way. This material is quite a bit more "springy" than the Creatology foam. I suspect this part was vibrating and adding its own resonances to the mix.

The 5mm Closed Cell Poly part seemed significantly less colored than the 10mm and had a sort of happy and alive sound to it. I did think this might be the best mod so far, but just the fact that it did have some character caused me to believe it was colored somehow and wouldn't stand the test of time, so I pressed on to the felt parts.

These last three parts are made of a layer of 2mm Creatology Foam with a layer of felt on top. The Foam Felt Wide seemed to have similar coloration to the 2mm Creatology Wide but without the piercing sound. It was nice to think I may have made headway in that regard.

The Foam Felt Thick has two layers of felt, and was actually the one I tried last. It was an improvement over the Foam Felt Wide, but it did seem a little thick and muffled compared with the Foam Felt Narrow I finally settled on.

The Foam Felt Narrow seemed to change the HD 800's characteristic transparency little, if any. You can see in the square wave plot it had the lowest amount of noise of any of the square waves observed. It bears a fairly strong resemblance to the stock square wave otherwise. Frequency response comparison against the stock headphone shows it within a couple dB of the stock headphone, though slightly flatter to 10kHz, and slightly lower in level above that. To my ears, this mod makes a remarkable difference. For me it does change the HD 800 from a headphone that's brutally honest, to one that's simply honest. I think it really is a worthwhile modification.

I need to add a disclaimer here: a lot of these changes were very subtle and having measurements available to me as I do the tests almost certainly has my head thinking of all sorts of things. There certainly could be a whole lot of confirmation bias going on as I do these types of articles. In other words, I can easily be fooling myself here, and all should be taken with a grain of salt. I am trying my level best to be unbiased and open as I do my listening, though.

If you're 98% of the way there (which the HD 800 is), and you make a 1% improvement, you've solved half the problem you'd been left with. The HD 800 is already the world's best dynamic headphone in my opinion. It images like no other. But in its stock form, it has a tendency to be a bit steely sounding ... or something like that. Hobbyists have struggled mightily with finding the right amps and cables to settle them down for a more enjoyable listening experience.

I think this mod suppresses the potential for ringing due to the hard surfaces in the HD 800 ear piece, and does a very good job of taking the edge off the HD 800 without otherwise changing its world class performance. While I'm glad to have had the chance to add my own two cents here, the design team at Sennheiser deserve most of the applause. And much of the credit for the mod goes to the guys mentioned earlier in the article, so I'm going to continue to keep referring to it by its current name: The Anaxilus Mod. I'm very glad the headphone hobbyist community continues to explore DIY headphone modification and improve its abilities along those lines, and I'm very happy to be a part of that.

Well ... the next step is yours.

Directions for the "Anaxilus Mod" to the Sennheiser HD 800


The finished mod installed in my HD 800 headphones.

Performing this mod is fairly easy. You simply construct the Foam Felt layered material by adhering it together; then staple the template to the material; cut out the parts with an exacto knife; then peel off the adhesive backing and stick it in your headphones. Rather than write a lot of confusing words, I made an instructional video that should be quite clear.

You'll need:

  • Printed .pdf template for the Anaxilus mod. You may need to turn off all scaling on your printer. (Print at 100%, no fit to page.)
  • A ruler
  • An Exacto knife with fresh blade
  • Tweezers
  • A stapler with about 16 staples.
  • One roughly 9"x12" sheet of 2mm adhesive backed craft foam (Creatology "Adhesive Foam Sheet," but any similar from a craft store should work.)
  • One sheet of craft felt (polyester, but I may experiment with other types of felt)
  • One pack of Aleene's "Tacky Double Stick Tape" or equivalent
  • The courage to to really take ownership of your headphones and start "cutting shit up."

The trainwreck that was iPodPJ's first HD 800 mod thread.
JaZZ's HD 800 mod thread where he slowly evolves from one solution to a better one.
Arnaud's first post on a Melamine foam mod, and his subsequent thread on the mod.
Purrin's "Anaxilus" foam mod thread.
What Hi-Fi article on how the HD 800 is made.
Head-Fi HD 800 appreciation thread and Skylab review.
Sennheiser HD 800 product page and brochure pdf.

Share | |
jocar37's picture

Great article. Got me really curious. Except I have HD700's. How do you think this mod would work on them?

Enter your InnerFidelity username.
Enter the password that accompanies your username.