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 www.audiocheck.net 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)
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: https://www.massdrop.com/article/understanding-headphone-reviews
And the Massdrop x HiFiMAN HE-350 is here: https://www.massdrop.com/buy/massdrop-x-hifiman-he-350