Review of the Hifiman HE-R9 JM OCD Extreme Stealth Edition Mod
Jun 29, 2022 at 10:33 AM Thread Starter Post #1 of 2


New Head-Fier
Mar 1, 2018
New Jersey, United States


  • Emphasized bass that is controlled
  • Highly resolving
  • Exceptional soundstage and imaging
  • Inoffensive high frequency range for laid back listening
  • Comfortable for long listening sessions due to being well distributed
  • Unable to use bluetooth dongle due to modification
  • Weighs 328g, something to consider for those sensitive to weight


Before I begin I must first mention that I bought this headphone and was not asked to write or post a review. As such, these are my genuine thoughts.

The headphone I'm covering in this review is a modification of the Hifiman HE-R9 headphone that was released in China in November of 2021 and was made available in US markets in the early part of 2022. The HE-R9 is a deviation from the usual offerings that Hifiman provides due to it being a dynamic driver headphone as opposed to being planar magnetic drivers that consumers have come to expect. It should be noted that both the HE-R9 and its big brother--the HE-R10--are both homages to the Sony MDR-R10 which has developed a cult following due to both its scarcity and performance, propelling it to legendary status among audiophiles. I myself have not been lucky enough to hear this headphone in person, but the consensus among those who have had the opportunity--especially back when it was released--is that it pushed the envelope of what was thought possible in a closed back headphone.

While that information may seem inconsequential at first glance, I feel that it is a key reason as to why the modder decided on modifying both the Hifiman HE-R9 and the HE-R10. I feel that in his own way, he aspires to "extend the legacy" of the Sony MDR-R10 by continuing to push the envelope in closed-back headphones the same way its obvious inspiration did. Now the question is: did he succeed?

Build and Comfort:

There are no modifications to the build of the headphone itself so, in effect, I'm reviewing the stock HE-R9's comfort. I've heard people state that the earcups feel like cheap plastic, one head-fier going so far as to say that the earcups feel "egg-shell thin" but I disagree. These earcups feel sufficiently sturdy without feeling too thick or brittle. They feel like they would be able to sustain a fall if they accidentally fell off of your head; but I'm not going to test that theory. The headband construction of the HE-R9/R10 is shared by the DEVA series and is a clear step-up from other Hifiman headband setups that feel cheap and, quite honestly, disrespectful to the end consumer. I used to physically cringe whenever I had to adjust the headband because the quality control was inconsistent and, at times, the act of adjusting the headband would chip the paint on the metal.

Aside from being built better, the headband is actually fairly comfortable, it's pleather wrapped around memory foam, and should be comfortable for mutliple hour sessions for the general listener.

The articulation of the cups both of the X and Y axis is fairly limited, but the headband is pliable enough for it to not be detrimental. The clamp force is satisfactory, it isn't too forceful while not being too loose. The weight of the headphone is very well distributed and feels lighter than it really is. It's about 328g which is lighter than the Focal Elex at 450g but understandably heavier than the Sennheiser HD 6XX which clocks in at 260g.

Sound Isolation and Leakage:

Although this is a closed-back back headphone, the sound isolation leaves much to be desired. With no music playing, I would be able to fully engage in a conversation with someone else at normal distance/decibel levels. Ironically, the sound leakage isn't too bad; and the earcups do a fairly good job at containing the sound. I don't have the stock version of this headphone to compare it to, but the JM OCD Extreme Stealth's (what a mouthful) have the inside of the cups lined with "heavy duty heat resistant sound liner," which is probably reducing the sound leakage.

Technical Parameters:

John Massaria, the creator of the mod, differentiates himself from others by using what he calls a 'fiberglass fractal mesh' to aid in the acoustics. He provides a visual on his website <> which shows a simulated render of the effect the fractal mesh provides on 3 frequency bands: 100hz, 1000hz, and 4000hz. Of course, that isn't the only modification he performs, but it is upon this foundation that he builds a uniquely pleasant sound that I had never heard before in any other headphone.

Taken from the product page:

fiberglass multi-pattern actually helps bring all frequencies out and expand them...the pattern I created here actually de-accelerates the sound waves into a very spacious sound "meshing" unlike fabric which has a deadening narrowing...this mesh material tunes the sound waves and it comes alive due to their fractal nature- and allows pinpoint accuracy and a wider stage fooling the waves into a creating a larger than life pattern while minimizing any echo or ring in sound waves - it works better than fabric (the idea comes from using much more expensive porous/foamed aluminum similar to ones used on the back wave of the Abyss AB 1266 TC or the Meta Material used in front of the Dan Clark Stealth or the Meta material used in the KEF speakers)

Another modification which I greatly appreciated is the direct connection between the 3.5mm port and the drivers. The stock version of this headphone has an intermediary wire between the left 3.5mm port that splits between the driver and a wire that goes through the headband to the right cup driver. This is to support the bluetooth adapter accessory. However, the way the 3.5mm port was wired internally also meant that not all third party cables were compatible, it depended on how the cable was wired. John has removed that cable and wired the 3.5mm ports in both earcups to the drivers directly for better connectivity. As a caveat, this means the mod doesn't support the bluetooth adapter, so be aware of this important detail if you're considering this particular mod.

Aside from that here are some other technical specifications:

  • Frequency Response of 15–35 kHz
  • Impedance of 32 ohm which means it's easy to drive.
  • Sensitivity of 100 dB

Pre-amble to Subjective Sound:

For context on my methodology for this review:

1). I listened to the HD-6XX with ZMF Perforated Lambskin pads for a month prior to my first impressions.

I knew I was in the market for a new headphone and I also knew I wanted to make a review, so I decided to listen to my HD-6XX's for a "mental burn-in". I figured that by getting reacquainted with a headphone that many people are familiar with, I'd be able to easily tell what the difference between these two headphones and--hopefully--articulate the differences.

2). I listened to songs that I was very well acquainted with. This compounded with my first reason.

I will also be listening to this headphone through the Topping D50 + Massdrop THX AAA 789. This pairing, in my opinion, offers the best price to performance of any setup I've heard.
With that out of the way, let's get into the sound impressions.

Subjective Sound:

This headphone surprised me for many reasons. The first surprise was the bass. When I tell you the bass is phat I mean the bass is PHAT. I'm talkin' like morbidly obese levels of phat. But that isn't to say that the bass is loose, uncontrolled, or bloated. No, my friend, the reason this headphone surprised me is because despite having the heftiest bass I've ever heard in a headphone it still--through some magic--is able to present the bass in an articulate and refined manner with no compromises. This headphone has a commanding authority in the way it presents bass. I can't overstate how powerful it not only sounds, but feels. On a track like Lose Yourself to Dance by Daft Punk the bassline extends deep into sub-bass frequencies, providing a smooth rumble, and whenever the kick drum is hit there's a palpable mid-bass punch. In all honesty, the way the bass is presented is reminiscent of a good speaker setup; you not only hear it--you feel it.

The second thing that stood out to me was how well this headphone presented the mid-range and handled resolution/transient response. This headphone's transients are fast. I mentioned how this headphone is able to present bass in an articulate manner with no compromises, and I mean that. If you've fooled around with EQ and attempted to bass boost your headphones, you'll know firsthand that a bass boost has an impact on the mid-range. If you boost the bass too much you run the risk of "muddying the mid-range" where you start to lose resolution and transient response in vocals and instrumentation.

To illustrate how good at resolving/transient response this headphone is, in the BBC live recording of Valerie by Amy Winehouse I am able to hear the initial twang in every bass note that's played. I had never been able to hear that before, even on my Focal Elex's. To be honest, it took me by surprise. I didn't expect to be able to hear new things in recordings I'm so well acquainted with.

One of my favorite genres to dissect a headphone's presentation, oddly enough, is Afrobeat music. Reason being that it's fairly minimalist. There's a beat, there's a voice, but most importantly, the production quality is amazing. In Damages by Tems the first thing I noticed was that I could hear the texture in her voice much better than on the HD 6XX and the instances of scattered percussion sounded much more life-like. I could even hear her part her lips 10 seconds into the song.

Speaking of texture...

String instruments in particular have never sounded so good. The fretless family of string instruments (violin, viola, cello, etc.) have a wonderful texture when played with a bow. One string instrument in particular is notoriously difficult to get correct: the cello. The cello presents a particular challenge because it has a beautiful mid-range, but many headphones struggle with presenting the lower frequencies which leaves it feeling inorganic.

One by Apocalyptica is a cello only cover of the Metallica song by the same name. It's my go-to song when analyzing cello presentation. I'm looking for three things when I listen to this song:
(a). texture
(b). low end presence
(c). hidden details like the musicians accidentally hitting the handle of their bow against the cello which happens a lot towards the final portion of the song.

Most headphones check the box on one or two of those qualities but I'm happy to say that the JM OCD Extreme Stealth gets it right. The trifecta is all there. The texture, the lower frequency, and the detail; it genuinely sounds like I'm in a theatre listening to the performance which is hard to do. Since this headphone has a heavy focus on bass I was expecting this song in particular to sound "stuffy" and cramped, but that's not the case here. Instead it sounds open, to the point where I feel like I can visualize in my mind's eye the dimensions of the room they recorded the song in. This headphone gives a great impression of dimensionality which is a perfect segue into the next portion: soundstage.

The soundstage in this headphone is also unique. The only way I can describe it is by saying that the soundstage is genuine. What do I mean by that? I mean that the soundstage doesn't exaggerate a sense of space, nor does it feel confined in a box. Is the song recorded with the intention of conveying space? If it is then the soundstage is vast, if it's recorded intimately then the song will sound intimate. This is another quality that I haven't heard in a headphone before. It is because of that quality that I feel like this headphone can lend a different lens to view music with.

Consequently, the imaging on this headphone is amazing.

There's a wonderful country song that I love to listen to in order to get a good understanding of how different speakers or headphones present soundstage/imaging called Hold On by Amber Rubarth. The song features a number of instruments and I can pinpoint with precision where on the stage (or recording booth) the musicians are.

The last part of the frequency response range is the treble region, and what I can appreciate from the JM OCD Extreme Stealth's is that the treble is tame. At no point did the high-end sound sibilant or hot; I never felt the need to turn down the volume because of sibilance which is a common problem I have with most Hifiman headphones.


If I had to succinctly capture my thoughts on this headphone it would be as follows: "this is the sound signature I've always dreamed of."

I used to think that there's always a trade-off between bass and detail.

I used to think that you'll never find a headphone that has both booming bass, and silky smooth mid-range detail.

I used to.

What John Massaria has done here is remarkable. He's somehow been able to create something that confounds my understanding. This mod of the HE-R9 is one of, if not the most, fun headphone I have ever had the pleasure of listening to; and I've owned or had extended listening time with a decent number of good headphones such as
  • HD800's
  • HD6XX/600
  • Hifiman HE1000
  • Focal Clear/Elex
  • Modhouse Argon Mk3
  • ZMF Eikon
  • ZMF Atticus
So who is this headphone for? This headphone is clearly tailored to those who like an emphasis on bass, but I'd also argue that every audiophile should have at least one headphone or speaker setup that is "pure fun", even if you favor neutral or analytical sound signatures.

Because I've said so many positive things about this headphone I feel it necessary to mention that John has not asked me to write a review; I am doing so because I genuinely want others to experience his work.

Still, I want to say thankyou to John for making these headphones, your passion and dedication to the craft is astounding, and I will be keeping an eye out for any of your new projects.

Keep up the good work.
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