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

Why would one of the world's best headphones benefit from a tweak?
For the same reason we have aftermarket car parts to modify stock cars: manufacturers have reliability requirements that make producing hot rods problematic. The modification I'm going to show you will not last as long as your headphones and you'll probably have to make another one within five years. This wouldn't be acceptable to a manufacturer. Sennheiser could surely make a better part than I, but in principle having some sound deadening padding adhered to the inside structure is a bit messy.

It also appears to me that the mod shown here does something similar to the removable liner in the HD 800, so Sennheiser engineers have already done things to address damping in the headphone. My guess is that the stock HD 800 is a terrific compromise of many, many issues --- most of which none of us will ever know or appreciate --- but in sum I find it the highest expression of headphone engineering to date.

That said, the stock HD 800 remains a tad hard on my ears, and many headphone enthusiasts have expressed similar sentiments. Over the years, a tweak for the HD 800 has been developing in the enthusiast community at Head-Fi.

I have prepared a companion .pdf booklet for this article that includes the Anaxilus Mod template, frequency response comparison graphs, and full data sheets for all measurements done in this article. It also includes four recent measurements of the stock HD 800, which were done on different days. These are labeled B thru E.

Evolution of the Anaxilus HD 800 Mod

sennheiser_HD800mod_Photo_ipodbjmodiPodPJ --- It all started when iPodPJ put a a little strip of T-shirt material into his HD 800. Much hilarity ensued and the thread is worth a read for that reason alone. But the fact remains: it's his little tweak that was the first evolutionary step to tame the brightness of the HD 800.

sennheiser_HD800mod_Photo_jazzmodJaZZ --- Wanting more bass than he was experiencing, JaZZ started modifying the HD 800 by putting some fabric into the headphones to block some of the escaping sound and get some more compression for the low notes.

His attempts to make changes and play around with sonic characteristics of the HD 800 inspired Arnaud (who is an acoustics engineer) to make some attempts. Their dialog helped JaZZ to eventually conceive the 3-layered velvet mod shown in the photo to the right.

I also think he's most correctly identified the problem these mods are addressing:

"...the main effect of the mod is the reduction of inner reflections, the reduced treble intensity is the result of reduced parasitic transient corruption"
Close enough. I'll go into more detail later in the article, but I believe the metal ring around the driver is acting acoustically as a reflecting surface and helping to promote a resonant mode that is storing a bit of energy. It is this very slight ringing at 6-8kHz, I believe, that some people find objectionable.

sennheiser_HD800mod_Photo_arnaudFEanalysisArnaud --- After being inspired by JaZZ's mod, Arnaud started playing around with some of the killer acoustics analysis software he gets to use for work. First in a post in JaZZ's thread, and then after starting his own thread, Arnaud tells us about getting a Melamine sponge as a small gift at work and then goes on to describe it's very cool acoustic properties.

Shown in the images to the right, he built a computer model of the HD 800 driver and enclosure, and then ran a finite element analysis of the acoustic response inside the chamber at 6500Hz both with and without his little block of Melamine foam in place. You can see that the distribution of sound is more even with the foam, which removes a hot spot near the rear of the driver. Here's Arnaud's explanation:

This is a plot showing the distribution of sound pressure level in the earcup in the baseline configuration, you can see reflection off the frame and observe that sound field is dissymmetrical. I am not sure about this but have a feeling this contributes to the HD800 "fuzziness." The soundstage is very wide and deep but placement is not so precise in stock configuration. I think reflections off the frame can be a cause for this.

Like JaZZ, Arnaud too slowly evolved his solution. Instead of velvet, he used 5mm thickness Melamine foam around the driver. Both reported significant improvements in reducing the biting characteristic of the HD 800.

sennheiser_HD800mod_Photo_anaxilusmodThe "Anaxilus Mod" --- The problem with the above mods to the Sennheiser HD 800 is that they require quite a bit of patience and skill with a blade to cut into proper shape. Head-Fi members Anaxilus and Purrin were chatting one day, and decided to do something about it. I sent a message to Anaxilus to get the full story, here it is in his words:

I/We had read about and tried the Jazz mod and purrin mentioned Arnaud's measurement simulations so we talked about the HD800 more and I said, "fuck it, let's cut some shit up." Purrin scavenged a bunch of stuff he had lying around (i.e., stole craft materials from his kids) and after much cutting, the Creatology Foam worked best to our ears so we stuck with it. Eventually it went from just a basic ring to include a precision trapezoidal area then also to a black version of the foam for aesthetics.

Purrin has also been a great source of information for headphone hobbyists by developing a measurement system that produces cumulative spectral decay (CSD) plots. CSD plots (sometimes called waterfall plots) show you how quickly acoustic energy decays after you turn the sound off. At the top of the plot, the headphone is excited with all frequencies; the audio level is shown both in elevation (z axis) and in color (red for high volume level, to blue and then black for low level).

In the plots to the right, the bottom axis is frequency and labeled left to right: 1kHz, 5kHz, 10kHz and 20kHz. Time is on the Y-axis and is labeled at right in one millisecond intervals. The stock HD 800 performance is very good --- much better than most headphones --- but we can see a bit of stored energy in the unmodified headphone as a turquoise blob centered at about 5.5kHz. After modification, the headphone shows a significant reduction in the amount of energy being released there. However, a couple of blips at about 9kHz and 15kHz appear after the mod.

It was after seeing these CSD plots that I decided to give it a go. Let's have a look at what I found ...

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thune's picture

Great work Tyll. A complete report like this is worth 10,000 forum postings about mods. This consolidation of previous work and exploration of materials was very engaging.

My question would be: can one get good results with a notch filter? (Either in EQ or with a passive network.) Can you get closer to what you want from the HD800 with signal contouring or with acoustical modifications?

Tyll Hertsens's picture
It's important to understand that it's not the driver putting out the excess between 6-8kHz, but rather that there is an acoustic "ringing" in the space within the earcup. Sort of like when you blow across the top of a bottle and it toots. Of course it's much less dramatic than that.

So, you can reduce the signal between 6-8kHz with an EQ filter so that the ring doesn't get excited, but of course then you're throwing away some portion of the music. Much better to damp the chamber with the mod, and keep the music properly balanced.

That said, for general use I don't see anything wrong with using EQ to to get the sound balance more to your liking, as long as the EQ filter (analog or digital) is of good quality. For audiophile and pro use, I find the phase shifts associated with EQing does damage coherence and imaging.

johnjen's picture

Well presented investigation and description of your findings, musings, and suppositions. :thumb

All of which help to make up the text for the circles and arrows on the back of the 44 full color glossy photographs, graphs and charts for all of us tweakers to ponder and mull over.

And truth be told Tyll pointed me at the many threads on Head-Fi where I 'got the bug' (thanks to Anaxilus, Purrin, arnaud, iPodPJ, JaZZ and the entire supporting cast of thousands ;-). And as we all know once smitten, there is no known cure.

And speaking of being smitten I think I see another variant that might just prove to be yet another tweak of a tweak. And because curiosity is such a marvelous motivation, I simply must explore it.

AND I have yet another level of exploration I'm pursuing as well, one that, so far anyway, is providing results as copacetic as this mod as well.

JJ :thumb

mward's picture

What a great writeup. I appreciate that both you and many of the hard-working Head-Fi-ers put some science into this. I'll take that any day over a few people claiming that something "just sounds better".

arnaud's picture

Hey Tyll, the least we can say is that, when you take interest in something, you don't just scratch the surface but really push as far as you possibly can. Another impressive write up, it's both thorough and consize at the same time, you got a talent for this!
Since you're always thinking outside the box as well, I am just eager to see all the other stuff you'll get your head around to this year ;).
Many thanks for referencing me and all those before and after who contributed, much appreciated :).

Jazz Casual's picture

I find these analogies unconvincing for the same reason that I don't accept the "surgical instrument" description for this TOTL headphone from Sennheiser. The HD800 is a state of the art dynamic headphone presumably designed to reproduce recorded music with a hitherto unknown level of fidelity.

It seems to me that "brutally honest" could be replaced with "hot treble", as the HD800's well documented treble peak has been too hot to handle by owners and "tyre kickers" alike. Many have found it so bothersome that they've resorted to all manner of methods to remedy it. Whether it be "The Anaxilus Mod", tube amps or after market cables, these are all measures that are being taken by HD800 owners to redress a perceived flaw in the way this headphone reproduces treble, and to beef up its bass presentation.

Fans of the HD800 say that it is extremely revealing of shortcomings in upstream components. Some of them advocate that the HD800 benefits from tube amplification because it relaxes this highly strung thoroughbred. Is this a situation where we can't handle the truth or is the truth as the HD800 presents it not entirely accurate and consequently, slightly unpalatable? Is it just possible that the problem lies with the headphone itself rather than everything that is attached to it, including us?

Does the Stax SR-009 require similar modifications to temper its rendition of "brutally honest" audio reproduction?

Tyll Hertsens's picture
Man, do you have problems with the world not being perfect?

In my view, the HD800 is an incredibly good headphone with one small flaw. Yes, a pebble in your shoe can make a walk in the park miserable ... especially if you obsess over it. Most headphones are a cluster of problems that may or may not sound good, and no simple mod is going to fix them. I place the T1 in that category; it sounds pretty good for the number of flaws.

I don't think the 009 images as well as the HD 800, and that's after spending more than double the money. Can't fix that.

I think you just like being negative.

Jazz Casual's picture

Let's not confuse how I deal with an imperfect world, with my response to the use of flawed analogies and pretzel logic in the discussion of expensive flagship headphones. And shoes don't come with the pebbles already added by the way.

With regard to the HD800, I take the view that if many of its owners are resorting to DIY modifications to temper the sound signature of a $1500 headphone, then it is far from perfect. Am I the only person who finds it rather absurd that those who are claiming the HD800 is the "best" dynamic headphone currently in production, are also the same people fiddling with foam mods, and throwing even more money at expensive tube amps and after market cables in the hope of making it more listenable?

mward's picture

I think you make some great points.

Philosophically, I believe in purely neutral audio components. Do people not like the HD800's treble because it's accurate and makes their bad recordings sound bad, or because they're used to artificially smooth headphones, or because its presentation is just that flawed?

Tough to say (especially since I haven't spent much time with this model). But I'm glad that someone ias asking these questions. i think the HD800 is probably a spectacularly good headphone, but there's no reason to take that as given just because it's one of the most expensive.

frenchbat's picture

Hi Tyll, great piece as usual. Please keep them coming !

Funny how felt appears to be one of the very best material when it comes to sound reproduction. I also ended up using some felt to mod my K702, and so far it's the best result.

Can I ask what is the thickness of the foam + felt material ? I'm using 2mm felt and I was wondering if doubling the thickness by sticking 2 pieces together would give me good results too. By the way: yes it's a PITA to cut this thing properly !

Tyll Hertsens's picture
Both the foam and felt were about 2mm thick. I felt doubling the thickness of the felt colored the sound a bit too much. YMMV.
frenchbat's picture

Ok, so if I understand correctly, you have 4mm total (foam + felt). I reckon that doubling it might simply be too much. Besides, the HD800 and the K702 are two different beasts altogether. The first one appears to only be needing some correction for a ringing, while the later could do with a slightly different presentation.

I ended up trying 4mm thick felt yesterday night. So far the details and the soundstage don't seem to have suffered much, and the treble peaks were attenuated a bit further than with 2mm of felt.

I also looked into melanin foam after reading your article, but this thing is really difficult to cut properly, and I understand why you left it out. The sponge form factor in particular is really hard to cut straight. I tried a 2mm layer, but it didn't work the way I was intending on the K702, and I doubt that adding some thickness would actually change anything.

Anyway, lots of fun playing with this. Thanks a lot for the article.

TheWuss's picture

here's a quick question / tip ...
must the felt ring and the trapezoidal area be connected?
why can't they be two separate pieces.
it seems the most tedious part of the procedure is tucking the trapezoidal area into the headphone.
if it was its own piece, that would be a cinch.

The Wuss

Tyll Hertsens's picture
You certainly could do it in two pieces, if you like. No problems.
jherbert's picture

Just curious: Arnauld chose melamin foam for its acoustical properties I guess - it is an open cell material known to be very effective in damping.

Is there a reason you did not try that stuff? In Germany you can buy small blocks of that stuff in every supermarket - it is used to remove dirt and stains.

Tyll Hertsens's picture
I was looking for a mod that was easy to do, and reliably consistent when people do it. Cutting the foam is a bit more difficult, and would vary a bit from person to person. None the less, I just may try it one day. I think I'll also try natural wool felt. If/when I do, I'll post results in a monthly update.
donunus's picture

Props to all the guys that contributed in the creation of this mod and to Tyll for compiling it into one article. Everyone with an hd800 needs to read this at least once.

Tyll Hertsens's picture
It's pretty easy to do, and I've fallen in love with my HD 800s. Use to be they were the best tool in the box, now they're my favorite listen.
Nuwanda's picture

Twenty minutes working time and the rest of my life to enjoy my new HD800. Now they're really easy on the ear! Can listen to music for hours with no fatigue at all.
Millions of thanks for making it soooooo easy for us, Tyll.

Skyth2nd's picture

I liked you walk through it was trough and seems like a good mod if you own the HD800. Your method seems like it works just fine so I may be splitting hairs here but I have never liked those adhesive sheets So you might try using a spray adhesive. and if you do that you could put the templet on the backside with it as well so you do not need staples. then pull it all off with the paper. Agin I know I'm splitting hairs here but the templet appeared to be rather deformed for the staples.

Tyll Hertsens's picture
DIY is one of those things where splitting hairs makes a difference sometimes. Maybe someone has a different idea, but the adhesive sheet wouldn't work. Your comment might give them an idea.


MacedonianHero's picture

So I got around to trying this mod and colour (sorry for the Canadian/British spelling) me impressed. It's smoothed out the treble to the point where its taken the HD800s from the perfect window into the recording to the perfect window into the recording's soul.

I wish I came across this mod before dropping a lot of $ on my Cardas GOLD cable, but such is life. Put the two together and these headphones are right up there with my LCD-3s as the best cans I've heard/owned to date.

Thanks Tyll for such a great write up and article. I love this place. :)

Tyll Hertsens's picture
Thankss,mate. I hope other do too. Be silly to bother with stuff like this if it wasn't worth doing.

Any body else out there give this a shot? Whaddaya think?

Windsor's picture

Just got my HD 800 today. :)

I've heard the HD 800 on a few occasions before, so I'm aware of its pointy treble, and after that very feature revealed itself as I played a few tracks earlier tonight, I decided it was time for the Anaxilus mod, so modded my HD 800 became. FYI: the foam I used was ~2mm thick and the felt was ~1mm thick.

I decided to clear my head after the mod was made, so I did, and with a clear head I now listen and am really, really impressed by the result!

There's no overbearingly harsh treble sound any more, just a healthy natural sparkle in the upper end. I've noticed it does get a little bit uncomfortably bright at times, such as at the end of Jimi Hendrix's "Still Raining, Still Dreaming" when the cymbal roll is happening. I'm not too keen on that as I don't want pain from my headphones, but I'll see how it plays out with different recordings.

I've not been A/B'ing the modded/non-modded sound, but from memory the bass seems a little bit muddier than without the mod, but the bass is still very clear with subtly powerful air-shifting heft.

Compared to my LCD-2 rev.2, which I've recently been using EQ'd to make more neutral-sounding, which has resulted in less bass bloom and veil (though at the slight expense of the LCD-2 timbre) and made the top end clearer (a definite improvement in clarity than the standard non-EQ'd LCD-2 IMO), the Anaxilus modded HD 800 takes the clarity to a level beyond that. The Anaxilus HD800's frequency balance is very close to neutral though ever-so-slightly treble happy, and to me music is very enjoyable through it so far.

I still love the warm tone of the LCD-2, which is like a wearing a warm pair of slippers by the fireplace, compared to the HD 800, which seems a bit like wearing a T-shirt on a breezy day that can get uncomfortably chilly at times. As far as my preference goes between the two headphones, I can hear that they're obviously different in character, and I'd like to listen more before drawing conclusions.

Tyll, one small question re. the anaxilus mod: the way I've installed one of the felt mod parts, it overlaps the circular metal piece surrounding the HD800 driver and covers the diaphragm very slightly, by ~1mm or so. Have you noticed if variations on the felt position around the metal ring affect the overall sound of the modded HD 800 in any way?

Thanks again.

Tyll Hertsens's picture
Glad you're enjoying the mod!

The overlap shouldn't be too much of a problem if it's small. I'd also caution you that you have some headphones that are extremely revealing of the gear driving it. It may be time to look at your DAC and amp for further improvements.

Windsor's picture

I'm currently using a Lavry DA10 as my DAC/Amp - any suggestions?

MacedonianHero's picture

EDIT, for the few weeks I had this mod in place I've come to the conclusion that in the end it took away too much from the brillance that is the HD800s. I found myself sacrificing clarity and detail too much. I have since looked back to my rig and changed/upgraded components over the past year that I feel this mod is no longer required.

Nebby's picture

Thanks for putting together all the information and providing the template that made implementing the mod a piece of cake! Picked up the materials today and just finished the mod. I'm listening now and I really like how it changed the HD800's.

Tyll Hertsens's picture
Nice! Glad to hear it!
mrog's picture

Does anyone know if Sennheiser themselves are doing something about the issue, i.e. ammending the design of the chamber on the same lines? I'm considering the hd800s so an upgrade like this in some near future might be worth waiting for.
Great to know there is a diy solution in the meanime, big thanks.


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