May 13, 2016

Headphone Modding

Hi Everybody. I’m Bill-P. You may know me from Head-Fi or SuperBestAudioFriends (formerly Changstar). I have done a lot of headphone modding in the community and have recently been doing some headphone modding for Massdrop. This led to some questions from Massdrop employees about headphone modding and why I do it. They thought you might like to know how I got into modding headphones and some of my ideas on how to mod. At the end, I’ll also share what I was able to do with the new HiFiMAN HE-350 in making them sound the way that I want them to.
Why do I modify headphones?
Basically, I really want to make headphones sound better for everyone and I think that manufacturers should hear how good their headphones can sound if they take more time to tune them. When you buy a high-end model, you expect that the manufacturer has already done all of the engineering for you- from tonality to frequency response to resolution. You assume you’re going to get great design and performance. These days, I typically modify because I want to personalize the sound, which is often what people are looking to do when they buy specific pieces of gear- like a tube amp or a DAC.

What do I want to change?
The start for me actually wasn’t the sound, but the looks that I wanted to change. I thought, “What would happen if I put wood cups on my pair of Audio-Technicas?” (Audio-Technica uses wood cups on their other headphones, like the ATH-W10VTG, and those look good.) Once I began tuning, I realized that using wood cups changes more than the looks; the sound will also change depending on the resonant properties of the cup. That was my “Aha!” moment, my realization that the material used to make the headphones really matters to the sound. I started looking around online and learning what other people were doing with their headphones. I had the ATH-ES10 and found that nobody else had modified them, so I decided to do it myself. The Fostex T50RP had a huge modification thread. That community was so crazy! It was a treasure trove of information on modding headphones, and I took all of my modding cues for my first headphone from there.
What’s the deal with measurement rigs?
I started out using a wand-type omnidirectional microphone (the UMIK-1) to measure the sonic frequencies of my headphones. One of the most effective methods I found early on was to rest the microphone on a pillow or soft surface, and then couple the headphone to that surface. That way, the mic is sandwiched between the headphone and the pillow surface. A good seal helps with bass response, and because that microphone was omnidirectional, it captured the midrange and treble response pretty well too.
Later on, I built a dedicated coupler that acts essentially as a headphone stand with the microphone embedded inside (as pictured above). This has allowed me to nail the seal more reliably and to get more consistent bass response than I did with the pillow method. Still, the pillow method is a decent option if you need to quickly check the rough frequency response of a headphone. To that end, I suggest you use your smartphone with a real-time spectrum analyzer app (like Octave RTA on an iPhone) and the Dayton Audio IMM-6 microphone as an inexpensive, quick-and-dirty measurement setup. Download and play a free “Pink Noise” file from and play that file while the microphone captures the headphone response and displays a graph on the app. Take screenshots before and after mods.
What’s my approach?
First, I do a “taste test” and listen to the headphone to determine what exactly needs to be done. Then, I try a few things that I know will nudge it back in the right direction and do a few more listening sessions with a number of challenging audio tracks that I know very well. After I’ve achieved a reasonable change in tone, I do some measurements to verify the results.

What are some different techniques?
There are many ways to approach a headphone. The first and most common thing that people do is stuff the back side of the enclosure with some kind of foam material, thereby dampening airflow and reflections. This will hopefully tighten up the lower frequencies. Swapping out the ear pads can also change the response in a very positive way, and I would argue that may actually be the most important change you can make to a headphone. The pads can absorb certain frequencies or change the distance of the driver to your ear, which can change how certain frequencies interact with the enclosed space. More advanced techniques involve putting things in front of the driver in order to obstruct and reduce higher frequencies and normalize the response of the driver. Other advanced techniques involve “mass loading” (in the case of mods with materials like Dynamat and Blu-Tack); treating the diaphragm of the driver (that’s what I suspect LFF does to his headphones); and what I’ve started dabbling with recently: using metal foil tape to improve the rigidity of the enclosure and intentionally induce reflections (I think that’s what is happening).

What are some materials you can use?
There are a lot of different materials involved in a mod. I think acoustic foam and various kinds of open-cell foam are the most popular types, but there are others with specific purposes—like Dynamat and Blu-Tack, which can be used to increase the mass of an enclosure and potentially change the resonance characteristics of the enclosure itself. Felt can be used to dampen reflections and reduce high frequencies when it’s placed in front of the driver. For a more dramatic effect, some modders will use toilet paper in place of felt. :) Closed-cell foam can be used very effectively to dampen even more reflection, as was done in the Anaxilus mod of the Sennheiser HD800. Rug liners typically have the same properties as closed-cell foam, with the added benefit of being more open.
What was my process for modifying the HE-350?
From listening, I know that this headphone runs into some trouble in the high frequencies, so the first thing I did was look to see what HiFiMAN had done to the front side of the driver. When I opened up the enclosure, I found a single layer of felt covering the driver. That, combined with the filter cloth of the ear pads, should have reduced the high frequencies—but it didn’t seem to be enough. I thought I would replace the felt layer with more layers of toilet paper (taking cues from Marvey) and other kinds of paper (like a medical face-mask filter or some tissue), since these are better at damping high frequencies. Then, I thought I could swap out the ear pads, since more distance from the ear to the driver and help get back some of the sense of “air” that the papers would get rid of. Just those very simple changes were enough to nudge the response of the HE-350 to something I would consider a really good improvement. The modification didn’t take that long to finish, and actually, the most difficult part was fitting the ear pads back on! The changes I was able to make are a sign to me that this is a good platform for modifying. I get a great sense of satisfaction that I want to share when I make headphones sound better.

The Results: Before (Blue Line) & After (Red Line)

Any Questions?
I will be travelling a bit during the summer and may have some issues with my internet connection, but feel free to ask me some questions or to discuss headphone modding. I’ll be happy to help when I can.
Also, you can read more about frequency response graphs here:
And the Massdrop x HiFiMAN HE-350 is here:

Add a comment...
Usually mods are made for bass improvement and treble dampening, that's exactly the opposite i want from headphones.
Anyway i have the HE400i and i removed the cloth behind the grill and i'm looking to replace the earpads with Ori earpads, do anyone know any other mod that may improve soundstage and treble?
People should be highly suspicious of headphone modding. It often appears to be a string of mods that attempts to fix the problems the last mod introduced until the result is something similar to stock that the modder pretends is an improvement.
I think most modders disagree; improving headphones is beneficial if you are careful.
(posting the link here to make it easier to find)
Easy bass boost mod posted by Will:
Is there any chance you could do a "wood mod" for he-350s or the m40x?
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The internet.. The best place to learn new things..
That's why I use it :)
"I'm just a caveman. I fell on some ice and later got thawed out by some of your scientists. Your world frightens and confuses me", but I would wait until you get your headphones and they have broken-in before you modify them.
cool post
Thanks Bill for the article. It's always great to see what other individuals primers are with regards to modding their headphones. Out of curiosity may I ask which ear pad's you tried and felt were best? Once I recieve my HE-350's after a period of stock listening will give them a little modding love thanks to you advice. Hope the travels are taking you to nice places. Chris.
Nice one! I some time ago modded my HD600s using butyl-rubber - some black self adhesive material used in car repair or housebuilding for making stuff water-tight.
i applied it on the plastics interior of the HD600s to maybe dampen some resonances and it worked like hell. Just has to be applied properly as it really dampens very good.
did you make the earpads? I want a set for my he-350's when they come
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Comfort or sound? Both will be subjective to your head and your listening preferences.
Ori Earpads are the best quality but they cost almost as much as the 350's
I envy Bill because he know so much on this topic and is not scared to get down and get dirty to experiment. (y)
Thanks for the interesting walk-through, Bill. I've always felt that the modding community plays a large role in keeping headphones relevant and on people's radar. It's great to see that the community is jumping head first into modding these new cans.

~Korotnam (SBAF/Head-Fi)
Sorry Bill. Just posted elsewhere that I'd asked you about this and the source of the "rumor" admitted it was his wishful thinking. Oh well..... LOL
Glad to see you here. You've unquestionably garnered an enviable reputation for tweaking headphones. Recently spotted a post that claimed there was a rumor associated with you, your mod guru position with massdrop, and Sennheiser. To wit, this post said they'd heard of a possible HD6x0 Bill tweaked future offering here on massdrop. Is it possible to confirm or deny?
A note on driver control (aka Newton's third law): When the driver moves to produce sound, the driver itself and the baffle plate to which it is attached vibrates in the opposite direction. This is the whole equal and opposite reaction thing. Things that vibrate the cup (either external factors or even the sound from the driver itself) will sneak back towards the driver as well. Now obviously, we don't want the driver to move at all. The more stationary it is, the more "pure" the sound that will be produced. There are three ways to accomplish this: mass, stiffness, and absorption.

Mass is literally that. Make the driver and baffle heavier, and it will move less from any applied force. Absorption is acknowledging that vibrations are there, but trying to squash them as quickly as possible. Stiffness is sort of this in between that affects the both. So let's address a few common things:

1) dynamat: It adds a tiny bit of mass, but primarily this is a shear based dampener. What that means is it has a layer of sticky goopy stuff, and a stiff metallic layer on top. When you stick it to something that vibrates, those vibrations move the goopy stuff, but the stiff layer on top doesn't move. This causes viscous shear in the goop which absorbs the vibrations.

2) blue tack, plasticine, etc: Common stuffing for baffle plates (especially Fostexen) to make them heavier. That's it. You get minimal absorption from this. Some people try attaching metal bits to the drivers to make them heavier, but that's generally difficult to do

3) stiffness: Things that have better bracing generally want to vibrate/resonate less. If you have a way to brace or stiffen a cup, it will move less. Increasing clamping pressure physically couples a headphone harder to your head. This is somewhat related to stiffness, and effectively connects the headphone to the mass of your head, and again heavier things will vibrate less (no jokes about being dense please!).

Annnnd, I think I had something else but I'm procrastinating from work and need to get back. Cheers y'all.
I'm not as active in the modding scene as I used to be, but I was quite involved in the earlier days of the ortho scene before Fostex madness took over. I am perhaps more notable for my driver transplants than my modding schemes. These days, I'm settled with my modded HE-6 and keep to simpler damping/modding schemes for my headphones.

For closed headphones, I almost universally stick some acoustic foam onto the inner cup surface (perhaps a rubber backed one if I want extra cup damping, or a dynamat layer first) and felts into cavity to reduce reflections as well as reduce enclosure resonance of external noise (which often magnifies midbass sounds). While some people like to use harder reflectors (like paper) or patterned arrangements of differing density materials behind the driver, I personally feel this creates an uneveness to the sound despite flatter objective frequency response. I find cups that are packed too densely also have a "dead" sound to them, despite again having a perhaps flatter sound. I used to spend a lot of time with rear damping, but nowadays tend to follow my general "recipe" with perhaps only a tweak or two before moving onto...

Front damping schemes; these used to be neglected in favour of rear mods, but they seem to be picking up now. Again, I have a general recipe here. It essentially boils down to covering every hard surface I can find with felt. Exposed surface around the driver? Cover it up. Are there paper filter covered holes on the baffle underneath the pads? Stick a ring of felt to give some air but also damp out the plastic. Is the backside of the pads a hard yucky plastic? Cut it out or snip in a bunch of holes. Etc.

For that matter, pads make a huge difference. The seal of the pads (both on your face and to the baffle) typically affects bass response, and the absorptivity/softness will play wonky with upper end frequency response.

My general lazy front recipe? just a big flat layer of soft felt that covers the entire opening and fits under the pads. Yeah it gets murky at times, but I'm also super treble sensitive so it works for me in the long run.