Headphoneus Supremus
Fir Audio Rn6 (Custom) vs. Xe6 (Custom) Comparison – Rn6 is a Xe6 with a more Audiophile Tuning
Pros: Exotic or God-tier performance, bone conduction that adds new tactile spatial elements plus bass for an entirely new listening experience that you can feel, best-in-class clarity and detail plus bass, full-sized performance. Adds more resolution over Xe6 answering some calls for those that enjoyed the Kr5 over the Xe6.
Cons: Not cheap.

NOTE: Based on feedback, this Rn6 review has been updated to be a direct comparison to its twin Xe6. They are both the same build using the same parts but have different tuning as outlined in this update.

: Fir Audio was listening to some of the Xe6 reviews of critics requesting a more treble-forward audiophile sound over the luxurious creamy Xe6 sound. Now both preferences are met with the introduction of the Rn6.

The Xenon 6 (Xe6) is Fir Audio’s next generation of their extremely popular M5, one of the best in-ears of all time when it was launched. The Xe6 from the new Frontier Series offers a very euphonic tactile sound with 3D sound staging moving from the M5’s more transparent and traditional audiophile sound with big bass. However, that came with a small but loud minority that was critical of the change preferring the next model down in the Frontier Series, the Kr5. The Kr5 sports the more traditional BA treble that is more forward and brighter overall vs. the electrostatic driver treble in the Xe6. Problem solved, Xe6 fans bought the Xe6 and the critics purchased the Kr5.

To showcase the capabilities of the 6-driver Frontier Series configuration and to answer the calls of those vocal critics, Fir Audio came out with a limited series Rn6 which amounts to a retuned Xe6. They took their Xe6 flagship 6-driver model and re-tuned it for a leaner, reference warm sound signature calling it the Rn6. So which is better…read on for the detailed answer…but in short, it depends on which signature you prefer.

Tour: Fir Audio Frontier Series – Xe6, Kr5, Ne4, Plus Rn6


For those that do not know me, I am active on AudioTiers and HEADFI under the username “Barra” and have been hosting product tours for almost a decade now. During this time, I have been able to hear all the greats and experienced the evolution of CIEMs/IEMs and all the associated equipment. From that experience, I can say without a doubt that Fir Audio has always been on top of all the lists in terms of performance and unique tuning capabilities. I have managed a number of tours for Fir Audio and am very excited to now offer another 2022 flagship tour for the Frontier Series. To sign up and to hear the Xe6, Kr5, and Ne4 for yourself, please go to the tour thread and follow the instructions:

UPDATE: As you might guess, we are now adding the Rn6 to our tour as soon as a unit becomes available.

As always, my goal is not to just offer my opinion but to offer tours so you can hear this equipment for yourself. If you are not already an AudioTiers tour member, please go to and follow the instructions in the “Getting Started” box on the Tours page:

Fir Audio Frontier Tour Kickoff Video

The Fir Audio Family

Fir Audio is a premium CIEM manufacturer out of the US that has a full lineup of premium IEMs and custom IEMs and is a longtime favorite on HEADFI and AUDIOTIERS. Their lineup has always made the top of the charts in performance including the M5, M4, as well as their Five x Five. To learn more about Fir Audio, their new Frontier Series, or to purchase the Radon 6 from this review, please visit their website at:


The Fir Audio Radon 6

The Xenon 6 and the new Radon 6 are Fir Audio’s new flagship IEMs available in both universal-fit and custom-fit models. The Radon 6 is a limited edition offering providing the same configuration as the Xenon 6 but at a different more treble-forward audiophile tuning vs. the lusher Xenon 6 tuning.

The Radon 6 is a Limited-Edition Anniversary model, the Universal-Fit model is limited to 300 production units world-wild. The Custom-fit model is limited to 100 units worldwide and only 20 units are produced per month. Celebrating 5 years in pursuit of the ultimate in-ear monitor listening experience.

Fir Audio has applied everything they learned from Frontier Series and mindfully returned our popular 6-driver model and arrived at a leaner, reference warm sound signature. Featuring proprietary technologies such as Kinetic Bass, ATOM Venting, Open Acoustics, and Rigid Technologies. It is offered at $3299.



The Radon 6 comes equipped with 6 drivers - one 10mm dynamic driver for lows which is fed into a Kinetic Bass port, 4 balanced armature drivers (1 bass, 2 mid, 1 high), and an electrostatic driver (EST) for the ultra-highs. This differs from the M5 that proceeds it on two counts – an extra BA for bass, and the Kinetic Bass port. This is enough to create an entirely new experience. The M5 is rated for 6.8ohms with a frequency range of 10hz - 20 kHz whereas the Xe6 is rated at 28ohms with a frequency range of 20hz -20khz although the Xe6 feels like it would be the one that digs into the 10hz range due to the kinetic feedback.

Several technologies are associated with the Xe6 including Kinetic Bass, Atom Venting, Open Acoustics, and Rigid Technologies. I believe that the Kinetic Bass and the Rigid Technologies are the only two new technologies that differentiate it from the M5 with Kinetic Bass being the star of the show. The Atom Venting is a key technology for me as it allows me to turn up the volume more without hurting my ears allowing a more dynamic sound in exchange.

Universal vs. Custom

As you can see from the picture above, the universal build on the Frontier Series is smoking hot – it even looks better in person. However, the custom options are stellar too – a huge improvement in options and appeal since I ordered my custom M5. You can see how beautiful the results were from my build experience – and yes, the other options were great enough that I often second-guess myself having desired several available options.

The universal format of the Frontier series all has a heft to them and a nice universal fit where I was able to get the majority of the performance offered by these monitors. While some may have perfect ear canals to get full performance from a universal, I do not so I did experience better performance from the custom version. This may be even more important for a bone conduction design as the tight fit that my custom offered me provides better contact with the bone conduction port which provides me with a lift in the effect vs. the universal option.


Based on the bend I have in my inner ear, I can only use the soft silicone tips to get a good seal, so I have not explored any other options. However, the seal provides great performance from the traditional sound port but does not affect the contact from the bone conduction port which is all about the fit of the universal paired to your outer ear. Therefore, your mileage may vary based on these considerations.

Custom Build Process and Unboxing

There is not much to say about a custom in-ear other than you can expect to get what you design and those premium manufacturers like Fir Audio put out stellar quality as you might expect. More importantly, Fir Audio has nailed all my custom designs in fit as this is the reason that I go custom…nailed it. Also are choices and ease of design which Fir Audio nails as well. For more insight into the Fir Audio custom build process or the unboxing experience, please see my Xe6 review where I detail both:

The Radon 6 Sound


The name AUDIOTIERS comes from my attempt to offer performance tiers to provide perspective on the various in-ear offerings and the surrounding gear that we are touring. While we have hosted mid-tier and some entry-tier IEMs, we have mostly focused on the top-tier offerings with some mid-tier options for those who don't wish to pay flagship prices. The best of the best are termed exotics for their ability to be unique and stand above the crowd. The top 5 of the exotics are awarded GOD-Tier status. The Xenon takes its place among those 5 GOD-Tier IEMs and the Radon is slightly different tuned twin is its equivalent in performance sharing this honor in that seat.

To describe the Radon signature in a nutshell – like its Xenon twin, it has the character of the Abyss full-sized exotic headphone. There is a clarity to the signature, but it is also euphoric and thick even though that sounds contradictory. While it is not the HD800-sized soundscape, it is large or full-sized in stature offering ease in hearing all the details that it serves up in gobs. While there are finer details like you might find in the HD800 presentation, it is more about sensory details and ambiance – that “being there” experience makes it feel warmer and more tube-like. Where the Radon and Xenon 6 stand alone from other god-tier performers is in the kinetic feedback that offers something new…a sound that you can feel as well as hear. This is different than other bone conductive earphones that I have heard/felt, in that it carries a broader frequency and in a more defined, clearer way that brings transparency with it. You have to hear it to know what I mean, so please join the tour.


The Radon and Xenon Sound Comparison


While they are very close in signature, there are some distinct differences. The Radon is more audiophile-tuned with treble forward while the Xenon is lusher and more set back. The Radon is like being on stage with the details in your face while the Xenon is seated in the front first balcony taking in the larger experience. The Radon is a slightly more intensive listening experience for detail nuts with gobs of detail in your face while the Xenon is a more relaxed listening experience for feeling the vibe and how it all comes together. They are both enveloping tube-like experiences, but the Xenon is more of a lush tube whereas the Radon is a cleaner tube amp experience. They are both huge in experience and explosive in bass and tactile feeling but seated differently within the event both offering that full-sized “being there” experience.

Optimizing and Pairing


As I did not find either the Radon 6 lacking in any area, I did not feel that rolling cables at this point would be a benefit. The stock cable is wonderful, and the resulting sound is more than satisfactory. So, this optimization section is mainly about pairing given that we have all already made investments in gear that we would like to use with our purchases. My preferred DAPs are the Sony WM1a and the Calyx M as I have sold my AK and other DAPs that were not being used. The Hugo 2 rounds out my setup by offering top-tier performance using my Sony or iPhone as a source. My desktop DAC/AMP is the Burson C3R offering 7.5 watts of pure performance to test the limits of scalability. Based on experience, the C3R wattage scales my dynamic drivers to the extreme but is not necessary for BA-only setups. Here is what I found.

  • iPhone 13 Max Plus: Amazon HD Music is a new app on my iPhone that has improved my sound quality considerably. From the standard Apple Music app, the Rn6 sounds great, but better on my better DAPs. The new Amazon app takes this up several notches and gets the iPhone closer to my dedicated DAPs mentioned below. The music discovery on the iPhone has made it my preferred method to listen to the Rn6 on the go. Either way, the music sounds full-sized from the iPhone, just more filled out with the Amazon app. But the dedicated DAPs are better overall. I just wish that I had access to the Amazon music app with these DAPs. As mentioned above, the only weakness of the iPhone is that in crowded or dynamic passages there can be some clipping at first. However, for whatever reason, the clipping seems to disappear, and the fullness of the note returns after the iPhone warms up with 15 minutes or so of constant playing. Of note is the need to turn up my iPhone to about 80 to 90 percent volume with the VE EXT vs. around 50 percent volume or less with the Rn6. The iPhone doesn’t feel colored in the signature offering a very revealing look at the Rn6 but may not extend to the extremes like my better sources. Ultimately, I would say that the Rn6 scales up better than it scales down but is extremely good on lower-end devices as well. Vs Xe6 – a final note is that I tend to choose the Xe6 over the Rn6 on the iPhone given the lower fidelity as the Xe6 is more forgiving whereas the Rn6 tends to expose the iPhone’s weaknesses.
  • Calyx M: The Calyx M is famous for its sound quality implying that the 9018 is responsible. While the stats don’t speak to this, the amp is likely to be the bigger influencer burning up a giant battery in less than four hours to meet that quality output. The clarity and transparency offered in the colder Calyx M signature offer more detail than the Sony below. In comparison, I used to like the Calyx M better than the Sony until I got a custom firmware upgrade on the Sony. The Calyx takes the audiophile performance up a notch with more and tighter detail, while Sony can be more fun. An advantage the Calyx has over Sony is that volume slider that allows me to perfect the volume for each song instantly and to play the Rn6 louder than normal for short bursts. This is more important for the Rn6 vs. my other non-vented IEMs as the ATOM system allows me to play louder without damaging my ears. The clarity of the Calxy M boosts the detail even more on the Rn6 and the powerful amp boosts the texturing. The M is a great pairing with the Rn6 offering a slightly different signature than the Sony which comes across as warmer and punchier. Vs. Xe6 - the Xe6 loses some of the tube-like euphonics on the M offering more clarity and finer details where the Rn6 stays treble forward. The pairing is perhaps better for the Xe6 to offer greater detail while retaining the euphonics, but it works great for the Rn6 as well.
  • Sony WM1a: The Sony was almost sold last year as it didn’t pair well with my CIEMs until I got the new custom firmware. The new firmware now plays nicely with all my CIEMs. The Rn6 pairs great with the Sony offering retaining its warm tint to its performance with a nice girth to the note and more resonance and textures. The Sony with its superior battery life and UX is my go-to DAP for the Rn6. The Rn6 signature is a little lusher on the Sony offering a nice pairing for slightly different tuning. In the end, the Rn6 sounds fantastic on Sony. Vs. Xe6 – both sound great, but the Sony offers a little lusher signature with the Rn6 making it a little easier a listen while retaining the Audiophile intent so I prefer the Rn6 over the Xe6 in this case.
  • Hugo 2: The H2 takes the experience up significantly on both the Rn6 and the Xe6 with a better DAC and AMP. The pairing is more in line with the Calyx M but on steroids. The bass comes out more – but cleaner with sharper edges and the fine detail is at another level. With the H2, the sound also gets fuller – more euphonic. However, as with the M, the H2 brings out the clarity/transparency of the Rn6/Xe6 making them sound faster for more of an audiophile sound rather than the more fun Sony. The problem with the H2 is that it is a stack that is not always convenient, so this is not as normal of a pairing as the Burson C3R which takes it up even another notch given the additional driving power if I have to deal with the inconvenience. The Rn6/Xe6 performance is significantly improved with the H2 with an additional gob of detail and is a wonderful pairing.
  • Burson C3 Reference: Going desktop, the Burson C3R is my favorite pairing supersizing the overall SQ significantly and in a fun musical way that crushes the Sony. It should also be mentioned that I am employing the Amazon HD Music application as a source and running it through my Sonarworks True-Fi application tuned to my HD800 headphones that work well with the Rn6/Xe6 signature. Playing through iTunes with True-Fi turned off brings down the sound quality noticeably, so some may consider this a cheat. Regardless, the C3R drives 7.5 watts into the Rn6/Xe6 and offers a significant boost to the low end with more punch and more clarity. While the C3R is slightly warmer than the H2, not by much. The soundstage also grows with the C3R. A traditional BA configuration such as the VE PHöNIX doesn’t handle the power boost as well having to keep the volume down to 1 out of 100 or it can sound overdone whereas the Rn6/Xe6 loves the additional overhead to drive the dynamic driver as well as to bring out more detail from the ESTs. My conclusion is that the Rn6/Xe6 grabs another boost in detail and soundstage with a quicker bass note offering peak performance – it is the best I have heard the Rn6/Xe6 sound.
Overall, I find that the hybrid/tribrid offerings like the Rn6/Xe6 sound their best when offered more power overhead and a more detailed, higher-end DAC such as with my desktop setup. While the Rn6/Xe6 sounds great scaled down to the iPhone, it would be a shame to not let the Rn6/Xe6 reach its full potential on a desktop system as well. Vs. Xe6 – finally, the Rn6 with its audiophile tuning is better suited for a higher-end setup as the flaws on the lower-end DAC/amps are very transparent.

Radon 6 Comparisons


The comparisons offered below are of the Fir Audio M5 for those choosing within the Fir Audio brand and of Vision Ear’s new PHöNIX and EXT flagships which seem to be the most commonly requested comparisons within the HEADFI community. To compare the custom Rn6 to the other IEMs, we used the sources described in the previous section. My music ranges from EDM to classical to rock to metal to pop to new age and easy listening – yes, I am all over the place. My preference in listening and comparison testing is to play all genres randomly to jolt my senses while getting a wide sampling of music. Here is what I found.

Fir Audio M5

The M5 is very different in signature than the Rn6. What they have in common is a very full-sized sound for a “being-there” experience and ginormous bass that is textured and life-like natural and exotic audiophile performance with gobs of detail. However, they offer this experience in two different signatures. The M5 can be considered more intimate while also having a wider soundstage with intimacy in the vocals and more space between instruments for transparency. The Rn6 of more tube-like romantic while retaining its clarity having more of a 3D involving soundscape with a new tactile feel to it. Both the Rn6 and the M5 allow you to get up close and personal with the singer. I may be overstating the differences to create a meaningful comparison as they both offer a full experience, but the experience is different. The Rn6 has a fuller stage which makes it feel more compact, but it probably can be better described as round vs. the traditional large width of the M5. What I am getting at is that there is just more information provided with the Rn6 to listen to as it adds atmospheric clues. This additional 3d sense probably comes from that tactile feeling provided by the bone conduction technology. Different from other bone-conduction headphones I have heard, the Rn6 seems to bring out a sound that you can feel in the treble range as well. As for bass, they both have that huge dynamic driver, but the Rn6 adds both the kinetic port as well as an additional BA dedicated to bass. While the M5 is no slouch with bass, there is just more information in the Rn6 output. I would say that while they are both fast, the M5 feels faster and clearer than the bass on the Rn6 which adds a lot of atmospheres to the equation. However, the Rn6 is more detailed. In the end, the Rn6 and the M5 will both have prominent spots in my IEM library allowing me to have two different exotic performance options to listen to my music library to hear it differently – win/win.


Vision Ears PHöNIX

The PHöNIX is Vision Ears' new flagship in-ear replacing their previous ERLKöNIG flagship. The PHöNIX has already gained a huge fanbase given its exotic performance and is likely to replace the ERLKöNIG in AUDIOTIER’s god-tier 5 lineup. As a traditional BA configuration with 13 BAs, the PHöNIX is easier to drive than the Rn6 which is a tribrid boasting both a dynamic driver as well as ESTs plus a kinetic port which all take additional power. Regardless, both sound wonderful on my iPhone, and both scale considerably on better gear. They are both top-of-the-game, god-tier performers with different signatures to enjoy your music library.

What is different about the PHöNIX vs. the Rn6 is most notable in the bass response. While the PHöNIX enjoys that Vision Ears BA bass mastery, there is no comparison to the much more powerful Rn6 bass which compares closer to the Vision Ears EST while still surpassing the EST given the additional tactile Kinetic port. If you are looking for bass first, the Rn6 wins. However, the PHöNIX is more romantic than the Rn6 which is quite romantic itself. I often make the comparison between high-end solid-state and tube-like tuning where the solid-state has more transparency, and faster notes with more contrast whereas the tube-like sound is more akin to warm, lush, and romantic. On that scale – 1 for solid-state and 10 for tubes, the PHöNIX is a 9/10 where the Rn6 is a 5/6, and the EXT being compared next is a 3/4. In the end, both the PHöNIX and the Xe6 are the best of the best with different signatures – the PHöNIX may appeal more to easy listeners and classical genres while the Xe6 will blow the mind of those that love more lively POP or EDM. The PHöNIX is one where you sip fine wine and relax whereas the Rn6 will get you up on the tables to dance. Your choice…


Vision Ears EXT

As mentioned above, this new co-flagship Vision Ears IEM is more solid-state in tuning offering an incredibly transparent experience backed by the second-best bass in the business. While the M5 could share that second-best bass title, it is more of an all-rounder where the bass is not as forward in the signature. The EXT doesn’t fool around, that bass is huge with a 10mm dynamic driver that is only beaten by the Rn6 due to that tactile kinetic bass port technology that takes it to the next level. However, the bass is not the full story with the EXT, it is an Elysium plus. The VE Elysium is known for its mids forward signature that is very unique and exotic in performance. The Elysium is my best of the best for mids, but this is the key focus there it is not an all-rounder, but it is my go-to vocals IEM. The EXT adds that incredible bass to the equation offering the full spectrum of sound taking it to flagship status making it one of AUDIOTIERS' exotic class IEMs. These two IEMs are both exotic and offer stellar sound quality. They both offer full-sized sound and an extreme frequency range with the power to drive textures and detail from end to end. The difference is mainly in the clarity focus of the EXT vs. the euphoric richness of the Rn6.

To summarize, the EXT is more solid-state with a lively signature and an extremely awesome bass response, the PHöNIX is at the other end of the spectrum with a more laid-back, rich tube-like feel in comparison, with the Rn6 being somewhere in between with an additional level-up in a 3D atmosphere with a sound that you can feel. The Rn6 is closer to the PHöNIX than to the EXT in terms of lushness but retains that 10mm dynamic bass excitement of the EXT. Again, the PHöNIX wins for easy or traditional listening while the EXT and the Rn6 win for more dynamic genres such as POP or EDM. They all sound wonderful with all genres but have the tools to take their favored genres one step further. So what do you prefer, solid-state or tube-like signatures?


Concluding Thoughts

The Rn6 is sure to wow any listener as a unique listening experience and an easy recommendation for those who can afford it. They offer peak performance checking all the boxes of modern technology and easily reach my exotic performance tier and are a candidate for my god-tier award. The only concern is for a more laidback music listener as this is an extremely energetic IEM that makes you want to get up and dance vs. sit down and sip wine. Regardless, if you live in the US, then you are free to join our Fir Audio Frontier Series tour to hear the Xe6/Rn6 as well as their lower-cost siblings the Kr5 and the Ne4 for yourself allowing you to decide for yourself – the way it should be.


100+ Head-Fier
Spooky Sound
Pros: Tremendous bass response
Airy mids create a sense of space
Spooky soundstaging
Technical capabilities are excellent
Cons: Coloured tuning may divide
Earpieces may cause fitment issues



Thank you to @Damz87, MiniDisc Australia ( and Fir Audio themselves for arranging this Australian tour of the Fir Audio RN6, XE6 and NE4.

The realm of top-of-the-line (TOTL) IEMs is often one that is undiscovered country for a large number of people within the hobby. I mean what’s the point of looking at something I know I cannot afford? I, for one, was in this realm of the hobby, sticking at the price point I could “afford” and being happily content in my collection of IEMs. However, after a prolonged period of exposure to people suffering with similar fixations on little speakers you shove in your ears, I thought to myself, “why shouldn’t I buy a TOTL, I deserve it” as well as other forms of mental gymnastics. Thankfully, before I blind bought something, I managed to get a taste of the TOTL life with these, the Fir Audio RN6.

And so, is the taste of the high-life something that is ultimately an exercise of “diminishing returns” or something that does not permit you to return to the realm of slightly more affordable (but nonetheless expensive) audio?

The Factual Stuff:

FiR Audio was founded in 2018 by Bogdan and Alex Belonozhko and Daniel Lifflander, previously at 64audio, they sought to begin their own journey with Fir Audio.

The Radon 6 (RN6) is a limited edition IEM celebrating their 5th anniversary and this particular unit is 1 of 300 units worldwide. Within the machined, black aluminium shells are a total of 6 drivers, with 1x “Kinetic Bass” 10mm dynamic driver, 2x mid-focused balanced armature drivers, 1x high-mid BA driver, 1 high-focused BA driver and 1x electrostatic driver. The housings feature a sapphire crystal glass faceplate containing within a carbon-fibre pattern interspersed with gold flake and featuring their rabbit logo and the name of the IEMs themselves.

The unboxing experience is rather straightforward from the understated packaging, containing within it, the earpieces, a pure silver shielded black cable, a variety of eartips, a cleaning brush, a hex driver to change out its ATOM modules and a leather case.

What are ATOM modules? Well the RN6 features a pressure relief system that utilises a number of modules to alter the amount of noise isolation and therefore impacts the sound signature of the RN6. The modules are:
  • Gold = 17dB isolation;
  • Silver = 15db;
  • Black = 13dB; and
  • Red = 10dB.
What is Kinetic Bass? A 10mm dynamic driver is nothing new but in the RN6, the DD is open and ported in manner that exposes it to the ear through the shell. This allows the bass frequencies to be transmitted to the ear in a manner that causes bone-conduction, usually a separate driver in other IEMs that seek to achieve the same effect.

The Opinion Stuff​


The following review was largely conducted using the silver module



I was rather sceptical when I read the “Kinetic Bass” marketing material, chalking up the rather lofty claims as being simply a means of spruiking their wares. However, upon listening to the RN6, the bass truly is physical in a sense. This is something I have yet to experience with any IEM on my journey so far with the exception of perhaps the MEST MK3 turned up to rather high volumes but the RN6 delivers a visceral and physical experience with its bass response.

I am happy to say that this is not merely a matter of pure quantity but rather the bass in the RN6 remains textured, detailed and fast. The physicality of the bass would lead one to believe that it would come at the cost of some bloat or some slowness imbued but the overall bass response of the RN6 is nothing short of amazing.

Extremely fast bass lines in songs such as “The Calling (Da Tweekaz Remix)” by TheFatRat, an extremely busy hardstyle song, remain wonderfully resolving and very visceral with its bass response. I could physically feel the air being pushed by the dynamic driver and the physical sensation of it on my ear. The experience is partly novel but the results in terms of discerning the detail and texture of the bass when listening cannot be doubted in my experience. The RN6 presents bass in an excellent manner.


Moving on to the mids, the RN6 does a rather good job at reproducing instruments and vocals in this area. The overall tonality and nature of the sound signature in this region is one that is rather airy and sparse in presentation. There is a ethereal character to the way in which it reproduces frequencies in this region, they seem to float out rather than come at you in a more aggressive manner.

Male vocalists in songs such as “7 Days” by Craig David are reproduced with gusto and a naturality that starts to veer on the edge of being overdone. There is hardly anything “digital” about male vocals but there is a loss of note weight in this region that seems to detract from having a hugely engaging experience.

Female vocalists in songs such as “Billie Bossa Nova” by Billie Eilish take front and centre stage that is more forward in the mix compared to the male vocals. Again, the naturalness and the airiness imparted in the vocals lends itself to a rather excellent experience.

Instruments such as acoustic guitar also are represented in a manner that is forward, resolving and natural in nature.

Looking to duets such as “Can’t Love You Anymore” by IU and OHHYUK with an excellent call and response in the bridge, demonstrates that the RN6 presents female vocals in a more forward manner where as male vocals appear to sit ever-so-slightly recessed in the mix.

Overall, the mid regions are reproduced with an excellent sense of naturalness and airiness that is hugely addicting. The way in which this works with the staging of the RN6 (more below) seems to yield the experience of listening to a vocalist live on a stage, say a 1,000 or 2 seater theatre.


Treble is perhaps the last thing on my list of elements that really jump out to me (unless its missing or making my ears bleed) but on the RN6, treble reproduction was executed in such a manner that distinctly stood out to me. It seemed to manage the balancing act of maintaining a level of elevation that imbued a sense of excitement and drama to certain songs, leaving me with a goosebump inducing listening experience without forcing me to yank the IEMs from my ears. “Reckoner” by Radiohead has a prominent percussion line throughout the entirety of the song that on lesser IEMs becomes entirely too much for my ears or is so undercooked that it remains distinctly unremarkable. The RN6 resolves this song with gusto, with speedy reproduction of the percussion in a manner that is crisp and wonderfully present in the mix without causing undue fatigue. The spicy chorus treble in “You & Me (Flume Remix)” by Disclosure tickles my eardrums where as other IEMs seemingly assault them. One element that I would have to criticise is that the uplift into the treble region is not exactly a smooth one and this becomes rather apparent in dynamic songs with large swings in volume and with lilting instrumentals wherein the ascent into a peak can be a rather jarring experience.

Overall, the treble has been executed rather well but I could definitely see how some would see that this is a rather energetic and exciting IEM that would eventually lead to some fatigue over time.


The soundstaging capabilities of the RN6 is a rather mysterious element of this IEM. The RN6 seems to adapt to each song in a manner that is almost spooky in its ability to predict what you’re listening too. Got an intimate acoustic song? You get a rather comfortable representation that makes you think that you’re in a theatre watching a performance on a small stage. Got something orchestral? You get an entire cathedral to yourself.

The depth of the stage on the Rn6 is rather great with a great amount of depth to the tracks that I had listened to that did not leave me wanting any more. The width also projects rather wide, something readily apparent with more panning instruments or vocal lines. The height is similarly great compared to the IEMs that I have tried so far (with the caveat that they all have been cheaper). But ultimately is the manner in which the RN6 shows a difference between songs that have been engineered to sound wide and songs engineered to sound narrow. Lesser IEMs either try to tune a certain level of stage width at the cost of depth, other IEMs are able to simply reproduce width rather well but ultimately these lesser IEMs do not seem to discern between the songs intent and rather imbues its own special sauce on whatever you’re trying to listen too. The spooky RN6 seems to enhance whatever the engineer wanted to do with songs reproducing a manner that seems fitting for their genre and the nature of the song in question.

In terms of detail and resolution, the RN6 is no slouch. Micro details are made readily apparent and perhaps to the detriment of the RN6, it is hardly forgiving in the upper end. Recording errors, vocal fry and the odd inhale are all laid bare in the reproduction of songs such as “Rush Over Me” by Haliene (Acoustic Version). The layering and imaging of all of my test tracks were done in a manner that made each instrument, each vocal line was readily discernible from another with no apparent incoherency in even rather busy tracks. “Fine” by Taeyeon is a rather popular test track with overlapping vocal lines by the same singer through a portion of the song that, on a lesser IEM, tends to sound like it is coming from the same “area”, but the RN6 provides the nuances in a manner that allows you understand I am receiving vocals from 11 o’clock, 12 o’clock and 1 o’clock readily.


One thought coming to my mind here namely lessons learnt after multiple DAPs, DACs and Amps plus headphones and IEMs is synergy!
Hoping for the one and only holy grail Setup is maybe just a nice wish unless buying according synergy transducers.
There's a reason why people are having multiple devices in parallel or reducing inventory and keeping only the ones with right synergy

Chord Mojo 2​

I would characterise the Mojo 2 as a very, very slightly warm neutral tonality with a more natural reproduction of instruments and voices with no DSP enabled.

The RN6 seems rather well represented on the Mojo2 as it presented the rather odd tuning in full effect. There is a bit of bite in the upper mids and treble but overall the bass and the mids remained rather enjoyable.

Experimenting with DSP features, I had learnt that the 10mm Kinetic Bass driver was highly capable with outrageous levels of boost in the low-end not leading to a complete collapse of quality.

Overall, there is not much to say here in terms of synergy, it works well and there is nothing in particular to point out.

Shanling M6 Ultra​

I would characterise the M6 Ultra (M6U) as a smooth, slightly warm source with an increased sense of presence in the mids and a strong note weight.

If there is one thing the RN6 and perhaps the XE6 and the Neon 4 do not need more of is warmth or note weight. The robust boost in the mid-bass on the RN6 is reigned in from the XE6 in my opinion but remains distinctly elevated when compared to a lot of IEMs in the market. The M6U seeks to enhance that even further and the result is a much more impactful listen. However, the added warmth and note weight seems to detract from more “lo-fi” produced songs with the low-end becoming overwhelming at times.

The M6U and the RN6 seem to work well if you wish to really lean into the tonality but overall I did not feel they were the best pair.


Vs XE6​

Compared to the XE6, the RN6 presents a much airier reproduction of music with upper-mid lift and a slightly less overbearing low-end. A-B’ing the two would have you believe that the RN6 is a much more neutral IEM which is true I suppose in the same manner that comparing the sun and candle would make you believe the candle is practically ice-cold in temperature. The RN6 remains distinctly coloured against other IEMs but when compared to the XE6, it is far more “audiophile” in its approach to tuning.

In terms of technicalities, I do not believe either really do imaging or resolution better but due to tuning differences, the RN6 appears to bring out the details in a more prominent manner. This tuning difference also creates a greater sense of layering and imaging in a manner that definitely helps the perception of “stage” as the RN6 seems quite claustrophobic in comparison due to the bass boost.

Overall, I believe that the RN6 is a safer bet for most people but the XE6 seeks to flex its muscles with its tremendous bass.

vs Neon4​

Where the RN6 seemed more neutral than the XE6, so too does the Neon 4. However, there is a distinct difference when A-Bing the RN6 and the Neon 4, whilst the Neon removes some of that low-end impact, it remains rather incoherent and odd in its presentation. The Neon feels overly smoothed out the mids are rather recessed, creating a sense of veil. The perception of resolution and technical prowess is loss and what remains is a rather underwhelming sound which remains enjoyable but when compared to either the RN6 or the XE6 there is nothing that stands out. This is a very unfair comparison considering the price difference and so feel free to read Neon 4’s review to compare it against some more similar IEMs in terms of price point.

Quality of Life​

The RN6’s earpieces are rather large and not exactly “sculpted” to the natural curves of the ear. It remains distinctly oblong and as such some fitment issues may arise. With that being said, the RN6’s aluminium ear pieces remain lightweight and rather comfortable to wear should they fit you correctly, causing no issues for me during long listening periods.

The cable is a rather decent one, adopting a 2 wire approach sheathed in some rather shiny (and slightly grippy) material. The ergonomics of this cable remain okay but not my favourite as I prefer more malleable cables.

The RN6 provides you with the ability to swap out ATOM modules to adjust isolation and affecting sound signature in the process. The differences were rather stark with red opening up things considerably, lessening bass and increasing the amount of outside noise let in. However, with the exception of the last point, the changes in tuning were not as stark as say, a tuning switch or what I’ve seen (in squigs only) in 64 Audio IEMs.

I do enjoy this ability however to alleviate pressure or isolate noise completely should you choose to in a manner that is not entirely obtrusive and rather effective. Just try not to lose the tiny things.


The RN6 is a 3,300 USD IEM. This is distinctly in the prohibitively expensive region but is this for good reason? The RN6 definitely takes chances with its tuning, seemingly completely different from a large number of other IEMs in the market, not even its price range and the gamble is a rather successful in my books. Despite being somewhat warm and having an aggressive bass response, it retains a very strong sense of technical capabilities. It is almost a paradox in an IEM, one would think that this tuning doesn’t work but seems to imbue a characterful and enjoyable listening experience. Now whether this experience is worth the pricetag? I would say no. I did not have any sort of out-of-body-experience outside of the novelty of the Kinetic Bass and just the sheer oddity of the tuning that really made me forget the asking price of the IEM. For those with cash to burn however, I believe the RN6 represents the road less travelled, a bit of a dark horse in the TOTL race.


The RN6 represents a more accessible sound signature in the Fir tour, with its airy mid-range, strong bass response and delicately balanced slightly spicy treble. It remains rather warm but not to the extent of the XE6 and whilst not ruler straight, it projects a more ‘audiophile’ tuning compared to the likes of the XE6.

For the price, I am reticent to recommend the RN6 but when viewed in a vacuum against the XE6, I believe it is the safer purchase. Technically proficient with a bass response that excels against the competition, the RN6 presents a coloured approach to tuning but the injection of air in the upper mids combined with its technical prowess presents a more versatile TOTL IEM compared to the RN6 and as such I can recommend it more.

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Great review!
I linked you some other great tracks over in the Fir thread.
As for the Haliene track! I have phone captures from her birthday stream during the COVID lock-down I really hope her husband (Mathew Steeper) recorded through the DAW. She did all her greatest hits stripped live and it was amazing. I'll have to go back and listen to the version you referenced!

PS: The red module in the Rn6 makes the stage even more ridiculous but some may find too diffuse, and I totally see why the majority prefer the silver for some more meat on the bones but ultimately the black when the silver is too spicy. The gold just tries to make the Rn6 its something that it didn't set out to be and detracts from all its top qualities (i.e. shoulda went with the Xe6 if you want the gold signature!)


100+ Head-Fier
FIR AUDIO RADON 6: Conceptualization the boundaries of sound
Pros: Sound, tuning, convenience, design, build quality and materials
Cons: Price
Hi friends!

After quite a long period, we return to the story of the most interesting new products in portable audio, and we have the most wonderful reason for this. Today our guests are our old friends: experimentators-modernists, virtuosos of the earphon engineering - FIR AUDIO brand.
Their recent flagship Xenon 6 IEM/CIEM made a lot of noise among audiophiles and professional musicians, captivating everyone both with its extraordinary approach to technical implementation, the amount of patented know-how, and the amazing sound of the model. The headphones turned out, without exaggeration, to be gorgeous. But there were also those who, despite all their love for customizing the flagship’s sound, wanted to add something and change it a little. Including bringing a bit of air, speed and expression from the younger, no less popular model Krypton 5 into the deep, mysterious and charming sound of the XE6. This is how, I believe, the idea of creating the hero of today’s review was born.

Radon 6 can be called a variation on the Xenon 6 theme, but with a completely different sound setup. Despite the similar configuration of elements, I mean the number of drivers, and the use of the same unique technologies, the end result has changed, absorbing the best features of both the KR5 and XE6.
Unfortunately, I never had a chance to listen to the KR5's, but one thing I can say for sure: having compared both six-driver flagships, I could not give preference to any one of these models. The RN6, like my beloved XE6, has everything to make you fall madly in love with this model.

Like all of the brand's IEM/CIEMs, the Radon 6 features a hybrid design. There are six emitters of three types on board: one dynamic (DD), four armature (BA) and one electrostatic (ESTAT). In addition, there is a replaceable Atom-X module and a unique design implemented according to the Tubeless Design principle - patented FIR Audio technology, which involves the abandonment of acoustic tubes and the open design of the drivers/emitters themselves, as well as KINETIC BASS - which you cannot hear, but you feel it! As a result, not only the acoustic design of the case, but also the very structure of the internal components have been carefully worked out in the earphones.

Well, it’s time to finish with the protracted introductory speech and proceed directly to getting to know today’s guest.


Text: Alexey Kashirskey aka Hans Barbarossa


Type: in-ear (IEM/CIEM)
Construction: hybrid
6 drivers per IEM/CIEM:
1x 10mm Kinetic Bass Dynamic Driver
1x OpenDriver Balanced Armature Driver for bass
2x OpenDriver Balanced Armature Driver for mids
1x OpenDriver Balanced Armature Driver for highs (with Sound Reflector)
1x OpenDriver Electrostatic Driver for ultra highs
Technology: Tubeless design, Atom Venting, Kinetic BASS, Open Acoustics, Rigid Technologies etc.
4 interchangeable Atom-X modules included
Freq. Range: 20-20kHz
Impedance: 28ohms
Cable: detachable - 1.2m/1.6m, connectors (2pin), jack-4,4мм

Music without limits: individuality or universalism

Initially, Radon 6 were released in a limited edition and exclusively in a universal IEM case, which is why there was serious unrest in the audiophile community. But now, before us, this model is already in the CIEM version, so now both music industry professionals and simply sound aesthetes have the opportunity to choose between individuality and universalism, ordering the RN6 either in a custom or universal version.

Well, for those who have not yet encountered CIEM, I can assure you that the procedure for ordering custom earphpnes is not at all difficult. You need to go to, register, go to the “Designer” menu, select the desired model, its design (appearance, connectors, cable length) and pay for the purchase. Then you go to the hearing center, make impressions of your ears there and send them to the manufacturer. After that, you look forward to the arrival of your exclusive CIEM.

In our case, the RN6 model is made in a custom design (based on an my impressions). And now it’s definitely time to move on to getting acquainted with the new product.

Appearance, kit, technology and ergonomics
On the outer wrapper, in addition to the FIR AUDIO logo in the upper left corner, there is a graphic design of headphones and three round icons indicating the technologies used in the model: KINETIC BASS, ATOM VENTING, OPEN ACOUSTICS.

The sides of the wrapper took on the brand logo and the inscription indicating that the headphones belong to the new line, “to New Frontiers”. Detailed technical specifications are indicated on the back of the package.


We remove the printed wrapper and find a black box, where we again encounter the FIR Audio logo in the form of bunny ears, applied in gold embossing, from which sparkling sun rays scatter in all directions.

In the box we find the RN6 themselves inlaid in a foam base with an already installed replacement cable (2pin/4.4 mm Pentacon), a black metal puck case designed for storing and carrying the earphones, instructions and a round colored patch-sticker “FIR Audio Space Force” .


Three pairs (silver, black and gold) of replaceable Atom-X modules neatly fit inside the case, and another pair - red - is already installed in the CIEM. Next, we take out a brush to care for the sound pipes.

Overall, the set is definitely five stars!

When choosing the appearance of my CIEMs, I settled on a glossy black shell, which is made of acrylic, and a similar gold-plated faceplate, with bunny ears on the right bezel and the model name "RN6" on the left. It turned out very beautiful, in my opinion.
On the faceplate, through the transparent varnish, we see a mesmerizing picture: in the resinous, rebellious sky, fragments and grains of a golden comet scattered, as if after a cosmic catastrophe. The beauty is incredible! This is not just a utilitarian device, but a miniature work of art!

The shell itself is made flawlessly, with every curve, every turn and bulge following the shape of my ear with surgical precision. Sound insulation is average, no worse or better than most CIEMs. The cable is supposed to be worn exclusively behind the ear.


At the bottom of the outer panel there is a replaceable Atom-X module. ATOM (Air Transfering Open Module) venting is a tiny metal cylinder valve that reduces the sound pressure exerted on the eardrum, thereby protecting hearing. It relieves the air pocket that forms between the earphone and the eardrum, and also acts as an acoustic filter, which serves to fine-tune the sound of in-ear monitors.

It is appropriate to recall here that the RN6 uses tubeless technology “Tubeless Design”. That is, the design does not contain acoustic tubes or separate chambers for drivers.



The sound pipe was covered with a removable metal mesh, protecting the headphones from moisture and sulfur. Another know-how of the company is used here - Rigid Snap Screen. Now you don’t need to unscrew the body to manipulate the protective mesh; just take tweezers, loosen and remove the pressure ring, then remove it and clean or replace the mesh. Although, I would still contact the manufacturer in such cases.
Next to the sound pipes is a round port of an open dynamic driver. This is an opening protected by a grille that transmits low-frequency signals directly to the cartilage of your ear. The same KINETIC BASS that you don't hear, but you feel!

A little higher, closer to the 2pin connector, you can find another small hole, which is connected to the fastening of this connector. RIGID Technologies is another patented technology that, according to FIR Audio, provides exceptional reliability, durability and ease of service for in-ear monitors.
“The most durable 2-Pin connection on the market, rated for 1,000 connections without issue. Fits any 2-Pin standard. Featuring a revolutionary quadrant socket design that prevents the socket from getting loose,” assures the manufacturer.



The included 26x8 AWG cable is made from pure silver and copper and is sleek and attractive. It is extremely light, elastic and high quality. Connectors 2-pin, straight jack plug, with balanced TRRS 4.4 mm connection. The splitter is made in the same style. The cable length is 1.2 meters. When ordering, you can choose other connectors and connectors, length, and also order a regular 3.5mm jack.

Like its brother XE6, the Radon 6 model has a hybrid design and is built on six emitters: one dynamic (DD 10mm), four open-type reinforcement (Open BA Driver) and one open electrostatic driver (Open Electrostatic Driver).
A speaker with “kinetic bass” is responsible for vibrations in the lowest part of the low-frequency register, one BA is responsible for the bass, its two brothers work out the middle, another armature is responsible for high frequencies and ESTAT is for ultra-high frequencies.


Well, FIR AUDIO, once again, turned out to be excellent CIEMs in all respects. But the most interesting thing, as you might guess, is still ahead of us: we move on to sound analysis. And this is, without a doubt, the most intriguing part of our review.

Phantasmagoria of sound: atom'ic tuning and life-giving neutrality (Sound Impressions)
Before listening, the CIEM were burn-in for 70-80 hours.
Sound equipment: MyST DAC 1866OCU V.2, Lotoo paw Gold, iBasso DX240, DX300, iBasso 220 MAX, QLS QA-361, iFI iDSD Diablo, iFi Gold BAR & iFi xDSD Gryphon.

With all devices, the RN6s sounded great, and their “voice” varied slightly depending on the sound source and the Atom-X modules used.

It is worth noting that replacing Atom-X modules significantly affects the sound character of the earphones:
Red - makes the sound open, fast, analytical and more expressive due to a slight accent in the upper register.
Black - the most neutral with good detail, with a little added weight in the lower register. It has a similar style to the red module, but has a less vibrant sound signature.
Silver - neutral with a slight added low end and deeper bass.
Gold - perhaps the most bassy with a slight accent in the upper register.


With all of the above modules, the Atom-X RN6 sounds great. But in my opinion, it's worth taking some time to determine which "atom" is best for you. Well, in the case of the universal (IEM) version of RN6, replaceable tips will have a certain impact on the sound too. Personally, after playing with these multi-colored modules for a couple of days, I opted for black, in my opinion, the most neutral Atom-X. With this in mind, we will conduct a general analysis of the sound.


The sound of Radon 6 can be described as well-balanced, smooth, with an excellent display of the emotional component, development of micro- and macro-nuances, excellent speed characteristics and amazing melody. The musical canvas is depicted in an unusually lively, bold, rich and contrasting manner, with excellent transmission of sound timbres and scrupulous elaboration of the details of the composition. This is a slight W-shape, presented in a neutral form.

RN6 create a fairly spacious and extremely detailed picture with an almost perfect depiction of the width and proportionate depth of virtual space. The precision of the sound of all timbres, coupled with a clean, neutral presentation with a slight touch of emotional coloring, amazes the ear from the first notes, creating a real sound phantasmagoria, dissolving us in the world of musical harmony.



Unlike its brother Xenon 6, which literally hypnotizes with its serious, deep, atmospheric, magnetic manner, RN6 sound more open, intelligible and balanced, showing a spreading stereo panorama, paying less attention to the depth of the image space, working more in width. In general, the Radons sound more clear, lively and emotional than the XE6. It's important to note that there is no winner here, as these models are complementary rather than competitors.

Radon 6 are able to amaze listeners of any background with their temperament, clear articulation, high resolution and wide dynamic range. Neutral, with a slight coloration at the edges of the frequency range, presentation, clarity, excellent speed characteristics - all this creates an extraordinary spirituality of audio images and completely dissolves consciousness in the sound pouring from the earphones. The audio canvas is drawn with contrast and clarity, where every stroke, every image is clearly visible.



The low-frequency range is presented tightly and clearly. The bass is fast, textured, with good texture development, biting, tight impact and excellent control. The sub-bass region flows smoothly and harmoniously into the mid-bass, which, in turn, vitally complements the mid-bass, filling it with depth, warmth and bodily substance.
A clear clap, shock vibrations - everything is transmitted and felt clearly, accurately and smoothly, without hum or encroachment on other registers. Well, a dynamic driver with KINETIC BASS technology allows you not only to hear the power of low frequencies, but also to feel it, to feel these tremors of the musical spheres.

Mids are neutral, smooth, with excellent texture reproduction and excellent resolution. Not a single detail will escape the listener.
The emotional component of the composition is conveyed in an extremely naturalistic manner. String instruments and wind instruments sound crisp and clear, guitar plucks are conveyed meticulously, vocal parts are filled with life, and the pianist’s nimble fingers delicately scatter over the keys - everything is beautiful, relaxed and with the right touch of expression. The timbre, vibration of a voice or the trembling of a string are conveyed authentically and deeply. Vocals sound slightly expressive, smooth and natural.
This is a well-balanced and at the same time sensual performance, smooth and spacious, where all elements of the composition are presented with unusual clarity and complexity. The positioning of tools in space is clearly calibrated and realistic.

High frequencies sound drawn-out, refined, intelligible, with good articulation, transmission of aftertones and enviable correctness. It's spread out, spacious, smooth and comfortable to serve. There is an elegant and light accent in this register that adds air to the compositions being listened to, but it is done competently and accurately. There is no excessive brightness here, but there is excellent refinement of this range and a natural, extremely musical sound without excessive harshness or distortion.


The Radon 6 handles any style of music without any problems. They play classical music, instrumental music, jazz, electronic music, rock, and brutal genres in an extremely interesting way.

Orchestra, touch: conclusions and finances
FIR Audio Radon 6 are extraordinary earphones that in both their versions (CIEM/IEM) are sources of music of the highest class! These in-ear monitors have their own charm and sophisticated flavor and will certainly find many admirers among the most demanding connoisseurs. It has everything: a balanced, clear and genuine sound that evokes a storm of emotions, the possibility of tuning, the use of the most advanced technologies, an original design, incredible ergonomics and a rich set.
Of course, the price of such a “delicacy” is also extremely far from ordinary. You can order Radon 6 in both custom and universal versions on the official website for $3,299.
Yes, the amount is very, very impressive, but the reality is that now this is exactly how much the sound costs, from which you lose peace and sleep, and even in such a stunning performance.

And if you have the opportunity to fork out for this magnificence, then I would recommend the FIR Radon 6 for purchase without the slightest hesitation.

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@Jwm48324 PT2.
The tonality is superb for both (I'm not sensitive to treble both are considered "spicy" by some; RN6 Silver/Red most spicy, Black/Gold less so), FR graphs aren't very predictive for these units if you're trying to do apples to apples with Harmon stuff. Your real decision is going to be the extra $$$ and can your ears accommodate the large shells of the Raven. The RN6 (the whole Frontier series for that matter) are nicely sized in the universal format, small even, compared to the big boys that are the EVO/Raven. Heck, even the EVO makes the Legend X seem small.

I own the EVO and RN6, have only heard the Raven. I like bass.
Are your shells the 'smoke translucent' variant? Great look. I'm strongly considering this as my next CIEM.

Great review! :)
FOUNDERZERO Yes, it's 'smoke translucent' variant' shell :) Thanks so much my friend


Reviewer at Ear Fidelity
Fir Audio Radon 6
Pros: The best-looking IEM on the market
Perfect build quality
ATOM modules
Superb case
Comfortable, snug fit
Fantastic cable included
Warm yet incredibly detailed
The soundstage!
Kinetic Bass is just the GOAT of bass in IEMs
Very emotional, fun providing sound signature
A technical marvel
Cons: Limited to 300 pieces
Only universal fit available

Fir Audio Radon 6 is a limited flagship-level IEM by the American manufacturer. It uses a single Kinetic Bass DD driver, 4 balanced armatures, and a single electrostatic driver. It's priced at $3299.

Introduction to the Fir Audio Radon 6 review​

Fir Audio Radon 6 box review

Fir Audio has quickly become my favorite IEM manufacturer in the world. While reviewing their previous flagship, the M5, I said that they’re really close to getting to the IEM Summit-Fi, and they achieved it with their next line.

When I reviewed their Xenon 6 it quickly became my favorite IEM to date, and I was sure that they’ll retain this position for a long time. Then, out of nowhere, the Krypton 5, which is actually a lower model to the XE6 came and absolutely stole my heart. My favorite IEM/Headphone ever, and it was truly worthy of winning our IEM and Product of the Year 2022.

Fir Audio really knows how to make a summit-fi IEM that sounds absolutely incredible, but not analytical and neutral at the same time. In High-End, it’s all about different flavors and original approach to the sound, at least in my opinion, and Fir Audio mastered that approach.
After the huge success of their New Frontier series, they came up with a limited model, the Radon 6. There are only 300 units in the entire world, so definitely, not everyone will be able to test it and buy it. With the price set between the Kr5 and Xe6, the Radon 6 is set to be a middle-ground of these two, providing the best aspects of both models.

And here, I want to say that I’m very grateful that I’m able to test the Radon 6, even though it’s such a limited product. With that being said, let’s see how the Radon 6 stacks against the competition.


Box of reviewed Fir Audio Radon 6

When it comes to the packaging, things are very similar to the Xenon 6 and Krypton 5. You’re still getting the same box with great graphic design and quality. It is inside of the box that matters truly, and we’ll just get right into it.

So, the first thing that is different is the new case. It looks quite similar at first, but if you have both the new case and the old one in your hand, it’s really easy then to see differences. The new case is slightly smaller in height, but it’s made differently, using better materials. The leather itself has a finer texture, giving a more premium look and feel. Additionally, even the bunny logo on top is now more prominent. It’s not that the old case is bad in any way, but when you’ll see the new one, you’ll immediately see that there was room for improvement.

Actually, the New Frontiers case was already one of the best cases I’ve used with IEMs, and I don’t think that Fir Audio got a single feedback to improve it. But, they just decided to do that…it’s a classic Fir Audio swag – It seems like they can always do better.


Next up, the rest of the accessories is nothing to write a book about if you’ve read our KR5 or XE6 reviews. The reviewed Fir Audio Radon 6 comes supplied with better eartips, which is always a nice thing to see, but most of you will probably end up using your favorite tips anyway. However, credit must be given when it’s due, and once again, Fir Audio just went the extra mile to assume that everyone is happy with their new IEMs. Nonetheless, adding Symbio hybrid eartips with the reviewed Fir Audio Radon 6 was actually a great idea, because these are by far one of the best eartips on the market and they actually suit the Radon 6 beautifully.
Apart from that, you’re also getting a cleaning tool, a set of Atom modules (more on that later), and a new custom-made cable. Fir Audio has always been a company that cares about the unboxing experience and the accessories you’re getting with your new IEMs. While this is by no means a luxurious type of experience, you really cannot say anything bad about it. Functional, elegant, and clean.

Design, Build and Comfort​


This might get repetitive, but once again, the reviewed Fir Audio Radon 6 shares the build quality and design with the New Frontiers lineup. And to be absolutely honest, this is the best thing Fir could have gone with.
The build quality and design are both top-notch with an astonishing fit and finish, as well as a beautiful design and infinite ergonomics. Fir Audio might be the company that offers the best build quality of every single IEM on the market, and the Radon 6 is obviously no different here.
So, to begin with, the RN6 feels extremely solid in hand, it has some weight to it, but not too much for it to be problematic in terms of ergonomics. This is a great balance between pure quality and comfort, which causes absolute zero worries when it comes to the durability of your new high-end IEMs. If you’re always taking your IEMs with you, and you don’t really want to be hyper-cautious about them, the entire new lineup from Fir Audio might be the best choice for you.

Actually, if you’ll somehow manage to ruin the connectors or the nozzle mesh, Fir Audio got you covered. Thanks to their Rigid™ technology, these parts are easily replaceable. Just sent your damaged IEMs directly to Fir Audio and they’ll have them fixed for you – How cool is that?! Obviously, I’d highly recommend caring about your $3000+ IEMs, to begin with, but it’s nice to know that if anything bad happens to them, the trash bin isn’t the only solution. Fir Audio offers a type of approach that everyone has to respect.

On top of the exceptional build quality is the design that just looks absolutely sick. This time, Fir Audio went with matte-black shells and sapphire crystal glass faceplates with carbon fiber and gold flakes infused into them. These IEMs look absolutely sick, definitely my favorite from the entire New Frontiers lineup. It’s just such a classy design, stealthy yet interesting, minimalistic yet refined. Just look at the photo above and appreciate this design, as it might just be the best-looking IEM faceplate ever.


Additionally, as I stated before in this review, the comfort of the reviewed Fir Audio RN6 is simply excellent. I can wear them for long listening sessions with not even the slightest sign of fatigue, even though it’s not the lightest IEM I’ve tried, not even close. It’s all about that well-designed shell size and shape that truly matters in IEMs, and Fir Audio got that covered brilliantly.

Lastly, the reviewed Fir Audio Radon 6 comes with a new, custom-made silver cable, that was built and designed exclusively for this IEM. It is a pure silver cable with copper shielding, and it’s by far one of the best-sounding stock IEM cables I’ve tested ever. Talk about attention to detail. However, the cable is a bit stiff and heavy, so keep that in mind if you are a fan of lightweight, thin cables that you quickly forget about. You’re not forgetting about this one, but the quality is definitely there. You can also choose your termination, I went with 4.4mm…for obvious reasons.


inner part of reviewed Fir Audio Radon 6

As I already mentioned, the reviewed Radon 6 uses the best technologies from Fir Audio, including the Rigid™, Kinetic Bass™, Atom Venting™, and Open Acoustics™.
At this point, you know what Rigid stands for, but let’s discuss the other ones.
Kinetic Bass™ is a technology that I already called a breakthrough in my Krypton 5 review here. The Kinetic Bass technology in the RN6 features a 10mm dynamic driver that is open and ported in an optimized manner directly facing the outside of the IEM shell. This design allows low-frequency sound to be transmitted directly to the ear cartilage and surrounding area.
Low frequencies are then converted to kinetic energy and reach the inner ear via bone conduction. This results in a more immersive sound with a bass you can feel, and it’s not just a theory. The bass of the entire New Frontier series is a breakthrough for the IEM market when it comes to low frequencies, and I’ll express upon that later in the sound paragraph.

Kinetic Bass makes the bass so physical, punchy, and pronounced that this is the only IEM in the world that you should consider if you’re a bass-head. There’s nothing that comes close for me personally. This feature gives that additional meat to the bone in the bass department, and the description of Fir Audio here is just spot-on, “a bass you can feel”.
Also, the reviewed Fir Audio RN6 incorporates the Atom Venting system, which helps reduce ear fatigue during extended listening sessions and at higher volumes. This system vents the pressure that builds up in a sealed ear canal, allowing for a more comfortable listening experience. On top of that, you can easily manipulate the isolation level by using different ATOM modules, which basically give you 4 IEMs in one. Those 4 different levels are:

RED : These modules give you the least amount of isolation (10dB), which gives you -4dB in the bass department when compared to the “neutral” silver module. This is the most technical, fast-sounding module, that lacks meat to the bone in my opinion. It definitely gets the least amount of listening time for me.

BLACK : These ones give you 13dB of isolation, which transfers into -2dB when compared to the neutral one, silver. It has more weight and warmth than the red module, sounding more natural and just more fun. While not being as analytical, it simply sounds more “right”.

SILVER : The silver modules are rated as N, which means neutral. It provides 15dB of isolation and is meant to be the middle ground. This is by far my favorite module, as it sounds incredible both technically and musically. Both objective and subjective sound is fantastic with silver modules, and I’d highly recommend starting with these, and then fine-tuning if you’d like. Please note: This review is made using silver modules, for the most universal sound descriptions.

Yellow : these modules offer 17dB of isolation, which gives a +2dB boost over the silver ones. This is the most bassy type of experience you can get with the Radon 6, and having in mind how incredible the bass is while using the silver modules, the yellow module is reserved for the most extreme bass heads. It hits the hardest, the rumble is just absurd, but it doesn’t sound as refined and natural as the silver module. My second favorite for electronic music and metal, but I prefer the universality of silver modules more.

The last technology used in the Radon 6 is Open Acoustics. This system in the RN6 eliminates the use of sound tubes commonly found in traditional IEMs. Instead, the open drivers radiate sound directly into a sound reactor, which shapes the sound using natural acoustics. This approach results in a much larger soundstage and a more pure and natural listening experience.
In terms of driver configuration, the RN6 features a tribrid system consisting of tubeless balanced armature open drivers, an ultra-high electrostatic tweeter, and a dynamic driver with Kinetic Bass technology. The specific driver configuration includes a 10mm dynamic driver for bass, 2x open balanced armature drivers for mids, 1x open balanced armature driver for high-mids, 1x open-balanced armature driver with a sound reflector for highs, and 1x electrostatic tweeter for ultra-high frequencies.
Reviewed Fir Audio Radon 6 has an impedance of 28 ohms, which indicates its compatibility with a wide range of audio sources. The sensitivity of the RN6 is not mentioned in the available information, but I’d rate it as quite average. All this makes the Radon 6 rather easy to drive, so basically every DAP will be able to handle them with no problem. However, note that these IEMs definitely do scale with better equipment, and I highly recommend investing in a high-quality DAP or DAC and AMP to use with these. Provide them with the best sound signal you can, and these will make good use of it.

How does the Fir Audio Radon 6 sound?​


The Frontier series by Fir Audio is what changed everything for Fir Audio. Previously, with the M-Series, Fir Audio established itself as one of the top IEMs manufacturers out there, but it needed that final touch to fight for the top of the top place.
The M-series definitely wasn’t the first thing that came into audiophiles’ minds when thinking about TOTL IEMs. However, instead of focusing on what they’ve already achieved, Fir Audio just went back and started tweaking and inventing new ways to improve.
You see, the new Frontiers series wasn’t just about “doing something new”, slapping a hefty price tag on it, and pretending it’s revolutionary. The amount of technology, research, and heart that went into it is just obvious once you spend even 10 minutes with either of the new models. While the Xenon 6 is incredibly fun to listen to, thanks to its warm, and incredibly thick sound performance, the Krypton 5 is the top dog in my opinion. Our “Product Of The Year 2022” is just an astonishing product in every aspect. This is the best IEM I’ve heard in my life, period.

So, Fir Audio now released the Radon 6, an IEM limited to 300 units worldwide, that is highlighting 5 years of Fir Audio. It uses all of the technologies that are present in the Frontier series and is said to sit between Krypton 5 and Xenon 6.
Let’s start with the bass. It is tight, controlled, and extends deep into the sub-bass region. It provides a solid foundation to the overall sound, adding weight and impact to the music without overpowering the other frequencies. Whether you’re listening to electronic music with deep bass drops or enjoying the rumble of double bass in jazz tracks, the Radon 6 delivers a magnificent bass experience. I’ve said it a few times already, and I will say it again – the bass response of Fir Audio IEMs is the best on the market by quite a margin.
The Kinetic Bass technology is absolutely incredible at providing a physical bass that you can both hear and feel, and it’s a fantastic sensation to experience it. At first, you’ll definitely see this bass as huge and overpowering, but the more you listen to it, the more you’re convinced that it’s the way it’s supposed to be and that you’ve been lacking bass energy with traditional IEMs. For many years now I’ve had a feeling that the high-end headphones and IEMs market focused on a bass response that is tight, controlled, and detailed, but it overlooked the fun factor, not giving us enough energy and power to simply headbang to.
Luckily, Fir Audio aimed to combine the TOTL qualities with a tuning that is pleasant to listen to, which was meant to give us a performance that will be both incredibly technical and enjoyable at the same time. They definitely succeeded, and that’s why I’m such a big fan of this company. There are a lot of high-end IEMs on the market, but none like this in my opinion. You’re not missing a single thing when listening to the Radon 6, you’re getting a complete experience, to say the least. Actually, after listening to the Radon 6 for some time, all of my over-ear headphones sound dull and powerless in comparison, even when plugged into the most high-end amplifier such as the Feliks Audio Envy.

Actually, Fir Audio IEMs are THE IEMs that changed my perception of the current headphones market. There’s just nothing like it when you can appreciate every single detail and godlike resolution, while also being able to get loads and loads of excitement when listening to every music genre. Metal and classic rock are not exactly the genres audiophiles go for, but with the Radon 6, there’s no reason not to do it.


Moving on to the midrange, reviewed Fir Audio Radon 6 continues to impress with its clarity and detail. The midrange is well-balanced and accurately reproduced, allowing vocals and instruments to shine. The sound is just incredibly open and clean, which also extends to the fantastic sound-staging performance (more on that later).
Female vocals have beautiful timbre and shine to them, resulting in a sound that is marvelously airy and realistic. Male vocals sound impeccable as well, with great thickness and note weight. Especially vocalists with low voices, benefit from the Kinetic Bass technology the most. As I said in my review of Krypton 5, Kinetic Bass also improves the sound of the rest of the spectrum, adding physicality and rumble.

However, keep in mind that this is still a rather thick and warm-sounding midrange, especially when compared to the Krypton 5 which is more neutral and crystal-clean sounding. It’s not as warm as the Xenon 6 though, resulting in a sound that sits in between being marvelously clear, detailed, and pleasant sounding. While the Xe6 could be too dark and warm for some, the reviewed Fir Audio Radon 6 still gets a lot of its remarkable richness, but now combined with a more open, airy, and crisp-sounding mids. This is definitely a more “safe” approach to the tuning, which will definitely appeal to a larger audience.

The treble response of the Fir Audio Radon 6 is detailed, extended, and well-controlled. The treble presentation is smooth and refined, allowing for an enjoyable listening experience, but it doesn’t hide any details at the same time. This is, again, not as safe or dark sounding as the Xenon 6, but still rather warmly tuned. There’s a lot of air in the top octave, resulting in fantastic soundstaging capabilities, which we will focus on in a minute.

What’s doing wonders with the treble of the Rn6 is definitely everything about female vocalists. Doesn’t matter if I’m listening to Tove Lo, Stevie Nicks from Fleetwood Mac, or Billie Eilish, the vocal range is always reproduced brilliantly with a timbre that sounds both natural and engaging at the same time. The sound has a sparkle to it, but it’s never becoming tiring or overly present. The level of detail is also top-notch, as you would have expected from an IEM of this price bracket. While tonality is slightly more on the “pleasant” side, the technical performance is simply fantastic. This is what you’re getting with good high-end products – a proper technical performance with a well-presented flavor profile.
The Krypton 5 is slightly more detailed than the two, pushing the boundaries even further, but to say that the treble response of the Radon 6 lacks detail, would have been incredibly too far-fetched. The Krypton 5 is a beast after all, so it’s not as surprising. However, if you’re into a more romantic and smoother sound experience, the Radon 6 might come as superior to the KR5 for you.

The soundstage is the part of this review that I’ve mentioned a few times already. Usually, IEMs with a warmer/thicker sound characteristic don’t do too well with the soundstage, but the Radon 6 is just built differently.
The sense of realism when it comes to the soundstage is absolutely brilliant here, with incredible imaging and infinite depth. The Krypton 5 is slightly wider-sounding, but the Radon 6 uses its warmer sound to its advantage here. Because of that, you’re getting a fantastic, black background with instruments popping out of nowhere, and combined with the Kinetic Bass that adds physicality to everything you’re hearing, this is a type of experience that is impossible to beat for other IEMs.

It’s actually quite interesting for a warm-ish sounding IEM to have a soundstage that vast and open-sounding, with such great separation. It works wonders with every genre I’ve tried it with, starting with electronic music, and ending with acoustic live performances of Eagles. When I said that the Krypton 5 is slightly wider sounding, I obviously didn’t mean that the Rn6 is narrow-sounding, not at all. It has a great width, but just not as impressive as its younger sibling. However, when it comes to depth, I’d call it a tie, and considering how much I praised the Krypton 5, this is very impressive.
There’s just so much air in the sound of the Radon 6, but at the same time, it has a lot of weight and body to it. This is definitely not your “classic” spacious-sounding IEM, mainly because of its beautiful tuning.

To summarize the sound of the Fir Aduio Radon 6, it is a technical-sounding IEM with an incredibly physical bass response, a slightly warm midrange, and an open, yet delicate treble. All of this is paired with a soundstage that is huge, and natural with fantastic imaging. If you’re looking for high-end IEMs with tons of details, the best bass response there is but at the same time you’d like a slightly thicker, warmer sound presentation, the Radon 6 could be just the best IEM in the world for you.


Fir Audio Krypton 5


This is probably the most important comparison in this review. While the Radon 6 is a limited model, it’s priced similarly to the Krypton 5, which has won our IEM of the Year 2022 and Product of the Year 2022 awards.
So, to answer the most important question right away – I think that Krypton 5 is a better IEM, at least for me. It is even more detailed, more open-sounding and its tuning is more natural. However, the Radon 6 is more laid-back sounding with more meat to the bone. Of course, you can alter both IEMs slightly thanks to the ATOM modules that are supplied. Because of that, you simply can’t go wrong with either.
When it comes to the technical performance, I’d give an upper hand to Kr5 thanks to its more neutral, technical tuning, but it’s not a big difference. We’re definitely speaking about minor differences, that could be irrelevant for you at this point. If you’ve tried the Krypton 5 and found it a bit too neutral for you, the Radon 6 is definitely the IEM that you should try next. It’s not a revolution, but rather a slight deviation from the marvelous Krypton 5 that could appeal to more people.
When it comes to the bass response, Fir Audio is ruling the game and they’re just playing alone on the playground. No other IEM can come close to any of the Frontiers series IEMs. When it comes to a comparison of the bass response between the two, I’d say that the Radon 6 offers a thicker note, while the Krypton 5 has better slam and attack, sounding more vigorous and dynamic. Which works better will highly depend on the music you’re currently listening to or pairing with different gear.

Dita Perpetua


The Dita Perpetua is priced similarly ($2999) to the Radon 6, so this comparison is needed as well.
The Perpetua is definitely a more laid-back sounding of the two. This is the IEM that reminds me of classic BBC speakers, with a sound that is so easy to listen to, yet extremely pleasing for long listening sessions.
Starting with the bass though, the Perpetua is not even close to the Radon 6, which offers a better extension, better physicality, slam, and raw power. There’s not even the slightest competition here, Kinetic Bass is just far superior to the Dynamic Driver found in the Perpetua.
When it comes to the midrange, the Perpetua is the more recessed sounding of the two, with lesser weight and less warmth. However, it’s also smoother and more intimate sounding, with its beautiful effortless type of presentation. The Radon 6 on the other hand sounds more dynamic, lively, and much more forward, with more body and presence.

The treble is definitely more detailed with the Radon 6, but it’s more easygoing in the Perpetua. High frequencies continue the trend of a sound that is just meant for chilling when speaking of Perpetua, while the Radon 6 is more expressive and has better sparkle, while not being harsh at all. When it comes to technical aspects, the Radon 6 is much better here, with better detail, resolution, and dynamics.
A similar story with the soundstage, where the Radon 6 is wider, deeper, and offers more sublime imaging. The Perpetua is intimate in comparison, but it doesn’t offer the level of technical superiority that the Rn6 does.

Fir Audio XE6


Now let’s compare the Radon 6 to the flagship of the Frontiers series, the Xenon 6.

The Rn6 sits in between the Krypton 5 and Xenon 6 when it comes to tuning. It’s definitely warmer and thicker sounding than the Kr5, but not as much as the Xe6. The Fir Audio flagship offers even more warmth, lushness, and richness to the sound, but it might actually be too much for many people. The Radon 6 takes those aspects and goes a bit easy on them, creating a sound that is going to be more oriented towards neutrality, but not quite there.

The soundstage capabilities of the Radon 6 are more impressive than that of the Xe6, with increased depth and better layering. The Xenon 6 sounds a bit more closed-off of the two, while the Radon 6 resonates fully with a vast amount of air around you.

Also, the bass response of the Rn6 is more dynamic and crispier, while the Xe6 is even more prominent and heavier sounding. This is going to come down to your subjective test, whether you’d like more impact or more body. Both IEMs are absolutely spectacular when it comes to bass response, so…choose your weapon.

The biggest difference between the two is that the Xenon 6 is a darker-sounding IEM in general. Because of that, it might sound less detailed and sparkly of the two. However, this kind of tuning definitely has its fans, and I actually enjoy the XE6 for its incredibly rich and cozy sound very often.

HiFiMAN Svanar

The Svanar is a current flagship of HiFiMAN when it comes to IEMs. This is a very impressive IEM that is both technical and enjoyable, with great dynamics and a fantastic soundstage.
The Radon 6 is definitely fuller-sounding, warmer, and more bassy of the two. The bass of the Svanar, while very impressive, isn’t really a match for the Kinetic Bass technology, both in terms of physicality and rumble.
The rest of the spectrum is definitely more neutral and flat-tuned in the Svanar, resulting in a more universal, natural tuning. The Radon 6 however has that richness that the Svanar sometimes lacks. When it comes to the technical performance, I’d say that the Radon 6 is slightly superior here, but it’s not a level of difference you should really be worried about.

Both IEMs are fantastic when it comes to soundstage, and I cannot choose one over the other. The Radon 6 has more convincing imaging, but thanks to the superior speed of the Svanar, the amount of air and separation you’re getting is just incredible. The soundstage is probably the best aspect of the Svanar, so it’s definitely not an easy opponent.
When talking about the sound as a whole, I find the Radon 6 to be more interesting. It has that timbre and richness that make the music more enjoyable for me, while the Svanar focuses more on the neutral and technical type of approach. At the same time, the HiFiMAN flagship is significantly more affordable, but the build quality is miles behind. For that, I believe it’s worth paying more for the Radon 6 – you’re getting a WAY better build quality and design, and the sound that is just more sublime, enjoyable and unique.

Fir Audio Radon 6 Review – summary​


Fir Audio once again released an IEM that is a force to be reckoned with. The Radon 6 sits in between their hugely popular Krypton 5 and Xenon 6. Not just in terms of the price, but the tuning as well.

This is a warm-ish sounding, thick and engaging IEM that doesn’t compromise technical performance. It comes with the worlds-best bass technology, incredible soundstage, and design/build quality that is simply the best on the market. While I personally still prefer the Krypton 5, I’d like to remind you that the KR5 is my favorite IEM of all time.

If you’re looking for a high-end IEM that does it all, has interchangeable modules to alter the sound and that is just a piece of art in every single way possible, buy the Radon 6 while you still can.

Highly recommended!

Big thanks to Fir Audio for providing the Radon 6 for this review. I wasn’t paid or asked to say anything good or bad about this product, all of the above is just my personal, unbiased opinion. Fir Audio hasn’t seen this review before publishing it.
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Excellent, articulate review. We differ when it comes to which Frontier we prefer, but that's the beauty of the series - you can't really go wrong with any of them!
@gLer thanks brother, I enjoyed your review a lot!

Yes, thats the beauty definitely :wink: for me, the kr5 is by far the best IEM Ive ever tried 😎
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Note that RN6 can be requested as custom as well :wink: I love mine!
Great review :thumbsup:


No DD, no DICE
FiR Audio Radon 6: A New Frontier
Pros: Naturally clear, revealing sound profile
Outstanding tonal balance across the FR, especially with default red module
Variable ATOM Xs tuning options
Exceptional build quality
Unique bass presentation, even at low volume
Cons: Price
Limited edition/availability
No CIEM option (officially)
ATOM Xs modules can be finicky
Might lack stage depth for some (compared to similar priced options)
I’d like to thank Vlad and @bogdan belonozhko for sending us a sample Radon 6 for this review, without any guidance or influence into how we’ll write it. Their enthusiasm for the community is infectious, and a big factor in FiR’s thriving popularity.


FiR Audio’s Frontier series has been making headlines for all the right reasons for the past two years or so. With so much new technology and innovation crammed into the three founding Foundation members: Neon 4 (Ne4), Krypton 5 (Kr5) and Xenon 6 (Xe6 – reviewed here), the series is a breath of fresh in a golden age of high-end IEMs already pushing the technical and tuning boundaries.

Towards the end of 2022, FiR decided to pull a rabbit out of the hat – as they do – and announce an all-new, limited edition Frontier series IEM, Radon 6 (Rn6), to mark the company’s fifth anniversary milestone.

Following the periodic naming convention of its predecessors, Radon is based on the same driver configuration as Xenon, but with slight design modifications, all-new tuning philosophy, and a specially-crafted cable specifically matched for its sonic profile.

Interestingly, FiR decided to release Rn6 as a limited edition set, with only 333 units expected to be made, at the time of writing. Unlike the other Frontiers, there is also no official option for an Rn6 custom, although several customs were made and sold under special circumstances.

Whether or not FiR continues Rn6 production beyond the initial limited sets, or indeed includes customs as a standard option, remains to be seen. For now, what we have is an entirely new and, sonically, unique IEM that, to my ears, has the potential to outshine them all.


Packaging and presentation

If you’re familiar with the other Frontier series packing, Rn6 keeps things consistent. Presented in a matte black box with a wire diagram of the IEM on a pullout sleeve, Radon’s packaging is minimalist at best.

Inside you’ll find a firm foam tray with cutouts for the earpieces and pre-attached cable, a round leather carry case containing additional sets of eartips, a cleaning tool, the ATOM Xs tray and an ATOM Xs removal tool, along with an iron-on patch to proudly wear the Frontier brand outdoors.


Unlike Xenon, which is supplied with one set each of soft silicone and foam eartips, Radon includes a set of Symbio hybrid silicone/foam tips, along with a separate set of foam tips. I’ve never been a fan of Symbio tips, finding them too hard and uncomfortable to even notice their sonic benefits, so I suggest experimenting with tips for yourself to find the ones that work best for you.

This is also good place to mention how finicky the ATOM Xs modules are to install. While the miniature design must have its reasons, practically-speaking swapping modules can be a pain. That said, FiR produced a video showcasing how to remove and install the modules, and I must say it made the process much easier to understand and follow. I’ve included the video here for easy reference:

Another thing worth mentioning is that the paint on the included modules, especially the red module, tends to flake off quite easily, leaving reddish residue in the ATOM Xs slot on the IEMs. If this bothers you, contact FiR and they’ll send you a replacement set of anodized modules, along with a cleaning kit for excess residue. It’s good to know the company has been so responsive to user concerns about this ‘tiny’ issue.

Radon and Xenon

I’ll be going back and forth between Radon and Xenon in this review simply because they share so many similarities, at least on paper. As such, it might be a good idea to read my Xe6 review if only as a primer to some of the tech I’ll discuss here briefly, though not as thoroughly as I did in that review.

Rn6 is packed with the same technologies FiR created for the entire Frontier series, including its breakthrough Kinetic Bass port and driver, ATOM Xs venting, open acoustics, and RIGID system.

By way of recap:

Kinetic Bass uses an outward-facing dynamic driver beneath an open-vented port above the IEM nozzle to transmit low frequency sounds indirectly through the ear cartilage, in a process known as bone conduction. This allows the full spectrum of bass energy to pass through your ears in the same way that it does using full-size speakers, which makes the bass feel more immersive, extended and ‘real’. It’s fair to say that FiR’s Kinetic Bass is different to the bass presentation on any other IEM I’ve heard.


ATOM (Air Transferring Open Module) venting is a staple technology on most FiR IEMs, based on similar technology to 64 Audio’s APEX (and its predecessor, ADEL) pressure relief system. It’s a brilliant technology that balances the pressure from sound waves pounded into the ear canal, reducing listening fatigue and, more importantly, protecting your eardrums.

The other, often overlooked, benefit of ATOM venting is the ability to fine-tune the sound by switching modules. Each module provides a slightly different level of sound isolation, from 10dB (red), to 13dB (black), 15dB (silver) and 17dB (gold). The higher the isolation, the more perceptible the bass levels, and therefore the overall sound balance across the FR. This makes Frontier IEM’s ‘tunable’ to some degree, in addition to other tuning methods like eartips and cables.


Open Acoustics is the umbrella term used for three different sound technologies inside FiR Frontier IEMs: tubeless open-top balanced armature drivers, a sound reactor that helps shape the sound projected into the internal chamber, and a sound reflector that directs the sound from the high-frequency (treble) driver directly into the ear canal. All three are said to improve sound fidelity and give the Frontier series its distinctive sonic balance.

Lastly, RIGID is also an umbrella term given to the series of resilient design features built into the Frontiers. These include a robust 2-pin socket that’s rated at more than 1000 cable connections, and a snap-on removable mesh screen that catches dust and debris from entering the nozzle and damaging the drivers. It probably should also refer to the Frontiers’ metal shells that look and feel as if they can take a real beating without suffering long-term damage.


Looking closer at Radon’s design, the Kinetic Bass port is slightly smaller than Xenon’s, though the bone-conducting dynamic drivers inside are the same size and type, as far as I know. Radon ships with an extra, default, red ATOM module, which also happens to be the least isolating of the black, silver and gold modules included as standard in the box.

Aside from these two fundamental differences, the size and shape of the Radon shells is similar to that of Xenon, although Radon is cast from a lighter, anodized aluminium instead of Xenon’s gold-plated stainless steel.

As such Radon is much lighter, though both IEMs are relatively small and light to begin with, especially when you consider how much tech is crammed inside. Radon is also finished in a matte black coating with a glossy black and gold-specked faceplate, making it far less ‘blingy’ than the gold and deep-blue Xenon hues.


If you get a good fit with the other Frontiers, Radon will be no different. If anything, it might suit you better if you prefer your IEMs featherlight, and I personally prefer the matte texture in ear to any of the other Frontiers, and while the nozzles are on the thicker side, the fit is still among the best I’ve had with universal shells.

I also prefer Radon’s all-new soft and pliable PVC cable to Xenon’s braided and twisty Scorpio C. It feels smoother, less microphonic, and better made, with 2-pin connectors and a gold-plated 4.4mm balanced plug to match, and fits right in with Radon’s dark, understated design aesthetic. Unfortunately, FiR doesn’t sell the cable separately, as it would be a decent upgrade for the rest of the series.

Retailing at $3,299 – a full $600 less than Xenon – you’d expect Radon to compromise on some of its sonic internals. Instead, it’s virtually identical, sporing the same 10mm Kinetic Bass dynamic bass driver, two open BA midrange drivers, one open BA upper-midrange driver, one open BA treble driver (with sound reflector), and one electrostat ultra-high treble driver. Both Radon and Xenon are also rated at 28-ohm impedance, and are very easy to drive (sometimes too easy, in fact).

I’m not sure where the price discrepancy comes in, and as you’ll soon see, why the asking price doesn’t reflect Radon’s relative performance against its bolder brother. Could it be that in creating a slightly more accessible version, in both price and tuning, compared to the ‘out-there’ Xenon, FiR has somehow stumbled upon an even better version of its original flagship?


Sound impressions

I’ll be comparing Radon and Xenon in more detail in the next section, but to start, let’s focus on Radon on its own terms. All testing was done using a select number of lossless and hi-res tracks from my flac and DSD library, which are referenced below where appropriate. Sources used include iBasso’s DX300 MAX, HiBy’s RS8, and Sony’s WM1Z.

Tonally, Rn6 has a quintessentially balanced, W-shaped tonality to my ears that spotlights bass, mids and treble in (almost) equal measure. It does this without over-emphasising any one frequency, or pushing any frequency to the point of harshness.

This is a clear, engaging, but even-paced sound that doesn’t go for ‘wow’ and instead creates a lifelike reproduction of the music you’re listening to in a very natural way – given the proper upstream source and file quality, of course.

There is colour here for sure; it’s not gregariously warm or thick a-la Xe6, nor is it neutral to a fault like some reference IEMs. Personally, I hear it as somewhere in-between, but to me it’s closer to reference than overtly coloured, especially with the red module (more on this later).


Bass has the distinct, deep, weighty-yet-open sound I’ve come to expect from FiR’s Kinetic driver, only it’s more evenly balanced between sub-and-midbass frequencies compared to Xenon’s midbass focus.

Even with the least-isolating red module, bass has a visceral rumble with oodles of texture, delivered in a tight, controlled way with zero bleed into the mids – until you switch to the more isolating modules anyway.

The electronic kicks in Aes Dana’s Inks seem to extend almost endlessly deep, with a satisfying weight you can almost see. It’s a subwoofer-like presentation that I really enjoy, more so than the ‘though the floor’ feeling I get from Xenon’s looser, more midbassy tuning. The edges of the bass notes are better defined, and while decay is slightly quicker, it’s still very natural with a quintessentially dynamic driver physicality.

Switching to ‘real’ drums, and the kicks in the Eagles’ live rendition of Hotel California hit in a natural, if slightly subdued way, closer to neutral than how I’m used to hearing them with more bass-forward IEMs. The texture and decay are all there, but the weight doesn’t steal the focus from the other instruments. Kinetic bass in general seems to come from a ‘deeper’ place, as if I’m hearing it emanating from inside my ears compared to more conventional IEM bass.

What Radon bass definitely doesn’t lack is texture. The latter third of Lana Del Rey’s A&W is replete with a wavelike bassline that feels like ripples of bass spreading across the stage. It’s a glorious experience with this IEM, even better in how it stays in its own lane compared to the various instruments, effects and Lana’s sultry vocals on this track.


Midrange tuning is another distinct deviation from Xenon, with a more ‘correctly-neutral’ lower midrange and gradual rise to a perfectly-peaked mid-to-upper midrange gain.

This does wonders for vocal purity, and as mentioned above, Lana Del Rey sounds absolutely exceptional with Radon. I mean, Lana sounds exceptional on an AM radio, but with Radon it’s as if she’s seated in the same room singing her latest poetry-music to an audience of one.

Gentle tracks like ‘Kintsugi’, ‘Fingertips’, and ‘Paris, Texas’ from her latest LP, Did You Know There’s A Tunnel Under Ocean Blvd, where her soft, sweet vocals are overlaid on a simple arrangement of piano and strings (and the occasionally-delicious sub-bass rumble) are as seductive as they are lifelike.

Vocals of the male variety are also very well done on Radon. Mark Knopfler’s distinctive twang on Dire Strait’s Sultans of Swing is set in line with, if maybe just a touch behind, his iconic guitar. In contrast, Leonard Cohen’s chesty drawl in In My Secret Life feels like it comes alive with the help of Radon’s Kinetic bass, while Justin Hayward’s Forever Autumn, originally taken from Jeff Wayne’s War of the Worlds, sounds iconically angelic.

Instrument timbre is another positive feature of Rn6’s midrange balance. There’s some organic warmth in the mids, likely from the Kinetic bass, but it’s not a veil as it sometimes sounds with Xenon, rather an accent. Mids have a fullness to them that sounds natural, for want of a different word, neither too wet or too dry.

Transients are crisp and full, the plucks of Ottmar Liebert’s Spanish guitar in Barcelona Nights sounding three-dimensional, perfectly mixed in with the congas and shakers on that track. Benny Andersson’s piano solo version of I Let The Music Speak is likewise delightfully subtle and nuanced, with just the right amount of weight and sustain on the keys.


Treble, and specifically the transition from lower to upper treble, is quite similar on Rn6 and Xe6, but Radon sounds more emphasised because of its comparatively less elevated midbass and lower midrange. Treble notes are still very clean, without any harshness, sibilance or peaks that I can point to in any of my test tracks.

There’s a slight lower treble emphasis, which makes poorly-recorded and already-splashy tracks even more so, but if your library is more sedate like mine, you’re unlikely to ever find this an issue.

Max Richter’s haunting strings in On The Nature of Daylight have a sweetness to them that cuts through with just the right amount of crispness. Similarly, his rendition of Winter 1, a recomposed version of Vivaldi’s famous The Four Seasons, layers the different string sections with outstanding accuracy, from the gentle intro to the soaring crescendo.

Listening for both male (Def Leppard’s Love Bites) and female (Missy Higgins, Shark Fin Blues) sibilance returns none on both, which is to say Rn6 is perfectly smooth in this region without losing any definition or blunting any of the transients.

While I wouldn’t call Radon’s treble the most extended I’ve heard, I’m also not particularly picky on treble extension. There’s enough air for my liking, especially on ‘airy’ tracks like Ilan Bluestone’s Will We Remain.

If you listen to a lot of treble-laden music and love your V-shaped sound, Rn6 might come across as slightly sedate for your preferences, but if you like your treble to keep its head down and stay in line with the rest of the music, that’s exactly what you’ll get.


Technical performance is, in a word, excellent – but with a few caveats. While I hear Radon’s stage as wide and spacious, it does lack some depth, but only in comparison to some of the best soundstage performers in the business (see Sony IER-Z1R below).

Listening to Owl City’s The Saltwater Room, I don’t hear any congestion at all, and there’s no sense that layering is compromised either, it’s just that sounds tend to trail off quicker to the sides and don’t linger in the centre stage as long as I’ve heard them do with some other flagships.

Imaging is accurate, Pink Floyd’s multitude of clocks chiming just where they should in Time, and Al Di Meola’s wandering shakers in Traces of a Tear almost making my head turn from left to right and back again to follow them.

Radon also excels in extracting all the detail in a track, particularly in complex vocal deliveries. I love how I can hear the subtle inflections in Heidi Talbot’s sugary voice in Cathedrals, and the fleeting murmurs in Angel Olsen’s delicate rendition of Chance. It may not be as resolving as ‘detail monster’ IEMs with artificially boosted treble or two dozen BA drivers, but it doesn’t need to be to sound as close to lifelike as I’d ever want for my own ears.


Speed and dynamics, check and check. Like Xenon before it, FiR knows how to build a dynamic IEM, and while Radon may have toned down some of the explosive excitement of its gold-hued brother, it’s still a top-class performer when it comes to volume swings, as a casual listen to Hans Zimmer’s Mountains will show you.

Overall, I find it hard to find any real ‘flaws’ in Radon’s tonal or technical performance, unless you call its lack of extreme colour or naturally balanced tonality a flaw. This is much more a ‘yes’ IEM than it is a ‘wow’ IEM. You can point to any of the previous Frontiers and describe a quirky characteristic that makes them ‘stand out’ from the crowd, but with Rn6, it’s more a case of everything just sounds right, just the way it should.

ATOMic tuning

As with all Frontier IEMs, the sound impressions above are written with an asterisk that says ‘subject to change on short notice’. That’s because swapping ATOM modules subtly but audibly changes the sound profile, and Radon is no exception. Instead of rewriting the impressions in four different ways, however, I’ve summarised the main differences between modules and how I hear them below:

Red is the least isolating and also the module I used to write these impressions. I’ll therefore describe the other three modules relative to how I heard Radon with red.

Black increases bass elevation across the board, though still manages to separate sub-bass without bloating midbass. Tonally it’s still a W, though bass-heavy tracks are skewed left compasred to red. Radon also sounds warmer now, the mids getting more glow from the bass boost, and there’s slightly less air in the treble, possibly as a result of the fuller mids. If you’re willing to give up some clarity and the last mile of treble extension, and prefer your sound warmer overall, black could be worth a try.

Silver starts to shrink the stage too much for my liking, though the bass boost becomes more prominent. Upper mids start to recess as the focus shifts downwards, though treble is still clear and natural, with plenty of sparkle and crunch when required. I don’t feel the technical hit is worth the compromise, but if you’re into a more bassy sound, this could be your preference. At this point I feel there are other IEMs that do ‘more bass’ better, and you’re losing too many of Radon’s strengths for too little return.

Gold is my least favourite module, turning Radon into a ‘mini Xe6’ but with blunted technical performance by comparison. Everything from upper mids northward gets a pillowy smoothness from the boosted midbass, and stage shrinks further, making it an even more intimate presentation than Xenon’s. If you crave a ‘different’ sound and don’t own a Xenon, it could be fun to play with gold once in a while, but personally I’d leave it in the tray.


Select comparisons

Xenon 6 ($3,899)
. If you’ve read the entire review to this point, you’ll already have some idea of the similarities and differences between Rn6 and Xe6. Despite having the same driver configuration and a very similar design, Rn6 is more than just a ‘retuned Xe6’, standing on its own as a very mature IEM and, in my opinion, the most ‘complete’ of the Frontier series.

That said, the most obvious differences, aside from their looks, is indeed their tuning, with Xe6 having unapologetically boosted midbass-to-lower midrange shelf, a very unusual and quite unique tuning choice for a high-end flagship IEM. This made, and still makes, Xe6 an outlier in terms of its warm, thick, enveloping sound, mixed with superb upper midrange to treble tuning that ‘breaks through the veil’ to deliver a simultaneously rich but also clear and engaging sound.

Rn6, in contrast, drops midbass and lower mids back down to ‘normal’ levels, especially lower mids that are now neutral. Midbass is still elevated, but only just, putting more focus on the sub-bass frequencies, with the corresponding elevation in rumble and lower-bass texture quite apparent.

This tuning choice puts Radon’s sound profile much closer to what I consider natural and lifelike, while retaining some of the fullness and warmth from its Kinetic bass driver. It also opens up the upper midrange with more air and significantly more clarity and apparent resolution than I hear with Xe6, although I find the relatively more forward midrange shrinking stage depth slightly in comparison to Xenon, which sounds more holographic.

Where the changes are most obvious is in tracks where vocals are closely mixed with instruments, and that contain at least some level of bass emphasis. This represents a large portion of my indie pop/female vocal collection, and any session with Xenon straight after Radon makes vocals feel more congested, the air warmed up, and a thicker coat of bass applied to the entire presentation.


I find Xe6 works well for thinner-mastered rock and EDM/electronic music with sparse, sharp instrumentation and effects, where the bass drone doesn’t stifle the final mix and gives the entire presentation a warm, impactful and highly dynamic feeling. This makes Xe6 a specialist IEM for my use case, and a hit-or-miss depending on what I’m listening to. Rn6, by contrast, is exemplary with most if not all of my music library, and sounds fantastic even when I’m exploring new music genres outside my comfort zone.

While technical performance is at least on par, I do find Radon’s improved clarity and midrange resolve adds an uptick to how I perceive its technicalities. With slightly shorter but still natural decay, especially midbass, Rn6 is also faster, and handles complex music with more composure and finesse than Xenon, which can come off as congested in busier passages, especially when there’s lots of midbass and lower-mid information in the track.

Overall, I find these two fantastic IEMs very complementary, as long as you have music in your library that gels with Xe6’s distinct coloration and don’t mind dropping nearly four grand on a specialist driver. Radon is easily the safest recommendation if you’re buying blind, and to me is the pick of the four Frontiers for its overall versatility. Here’s hoping FiR makes it a permanent fixture.


Sony IER-Z1R ($1,799). It’s no secret that Sony’s IER-Z1R is my favourite IEM, and has been for well over a year now. It has the tuning, technical performance and overall gestalt that ticks every box on my preferences checklist, and I’m yet to hear an IEM at any price that matches Z1R’s unique combination of sonic qualities.

But before we get to the sound, there are some key physical differences to consider between these two flagships. Z1R is, for some reason, notoriously difficult to fit for many people. As someone with smaller ears and narrow ear canals who’s never struggled with the fit, I can’t quite understand why. But then I’ve used many IEMs that don’t get any fit complaints, and with much larger nozzles, that I can’t get into my ears at all. Even Radon, with its thicker nozzle, is on the border of comfortable, and puts more pressure on my ear canals than the Sony.

Driveability is also different. Rn6 is much easier to drive, with the dial set at 9-10am on the DX300 MAX on average, compared to the Sony sitting at 1-2PM, both with low gain. The Sony also scales up more with more power from the source, whereas Radon sounds the same even from low-power sources like Sony’s WM1Z.


Tonally, where Rn6 is a flatter W-shaped tuning, leaning more bass-left depending on the ATOM module used, Z1R has a distinct U-shaped tonality, with bass and treble projected more forward, but – and this is important – so are most female vocals. Despite its tuning profile, Z1R actually has less bass elevation than Rn6, even with the red module, and while Z1R is mostly sub-based focused, you’ll feel more visceral rumble with Rn6 too.

Z1R’s bass has a uniquely liquid quality that seems to flow across the stage, gently texturing the lower frequencies and adding to the subtle echoes and cues that create its cathedral-like tall, wide and very deep stage. Radon’s bass is more centred, and doesn’t resonate quite as deep.

In fact, Radon presents sounds on a flatter plane, with bass, mids and treble more or less even on the stage, whereas with most of the tracks I used to compare the two IEMs, Z1R will have vocals and/or bass or some other element closer to me, with some sounds panned hard left and right, and others trailing off into the distance. As such I find Z1R more immersive, moving elements back and forth towards me, whereas Radon pushes my listening position a few rows back and keeps most of the action in front of me on stage.

If you’re looking for absolute slam and impact, Radon has the upper hand, whereas Z1R is more ‘polite’. That’s not to say it can’t slam, it’s just that Radon’s Kinetic bass is more physical.

Conversely, Radon’s mids, especially female vocals, are more revealing, and even though both IEMs are tuned for clarity in the midrange (especially upper midrange), I find Z1R sweeter and more natural, and Radon slightly drier by comparison. That said, Radon is more ‘correct’ in its placement of male vocals, so if you listen to lots of male vocal music, it’s probably a safer alternative.


Up top, Z1R has a bit more energy in the lower treble, whereas Radon spreads its treble energy evenly, and has more mid-treble presence. Radon also has a touch more air, but Z1R is more sparkly and pristine, with some of the best treble sweetness I’ve heard with any IEM. Neither IEM overloads the upper treble, which is very much in line with my preferences.

Technically I find both IEMs to be very much on par. They trade blows as to which is more resolving, both being just about as resolving as I’d like with top-tier performance. Both are also very dynamic, Z1R maybe a fraction more, but it’s splitting hairs.

I do hear Z1R as having a slightly darker, quieter background, but only because Radon is a touch warmer. Imaging and separation are also fantastic on both, with Z1R possibly pipping Radon for first prize. Neither can match the clinical performance of dozen-driver IEMs, and both are also more enjoyable to me than any dozen driver IEMs I’ve heard.

Overall, as close as it gets, Radon isn’t going to replace Z1R for me, but because of its even-mannered profile, is better suited as a benchmark IEM that all others can be compared to.

Both fit my target IEM profile of top-tier all-rounder, and both have their own strengths that make them complementary. That’s more than I can say for most other high-end IEMs I’ve auditioned in the past year, Xe6 and Kr5 included.


A note on pairings

I was going to write a separate section on different pairings for Rn6, only to discover that Radon is incredibly adept at adapting itself to the sources I have at hand. Whether I’m listening to it with the DX300 MAX, RS8 or WM1Z, I’m not hearing significant differences in the sound.

The subtle character of each DAP comes through: RS8 with its smoother, analogue vocals, WM1Z with its gentler bass and lusher tonality, and DX300 MAX with its clean, neutral power. But overall, I can enjoy Rn6 from any of these sources without feeling like I’m missing out on quality, resolving power, stage size or tonal balance.

There are many IEMs, like Z1R for instance, that are pickier about which pairing they sound best with. Radon isn’t one of them, and that’s a good thing in my book.


Closing thoughts

I could sense Vlad Belonozhko’s quiet enthusiasm when we ‘met’ on a Zoom call earlier this year. We were discussing this very review you’re now reading, and I could tell that there was something about this IEM that was special to him, aside from the fact that it was a special edition commemorative of FiR’s success as a company.

Fast-forward a few months and I now share Vlad’s enthusiasm, if not more so. In my Xe6 review, I mentioned how that IEM had taken the industry by surprise, rising to the top of the popularity charts for those that own – or have owned – just about every high end portable audio driver on the planet. Rn6 is not that IEM…it’s better.

Perhaps unsurprisingly, Radon isn’t lighting up the charts quite like its older brother. It doesn’t have the same bold tuning, or bling looks, or aura of unapologetic bashfulness. It’s a safer, more polite, more correct-sounding IEM, but make no mistake, it still has that FiR Frontier flavour: unique bass physicality, exceptional technical ability and supreme build quality.


For me, Rn6 is the culmination of everything FiR has learned in creating the Frontier series, rolled into the consummate FiR IEM. It takes the clarity and speed of Kr5 and the power and technical performance of Xe6 bass and combines them into a new Frontier derivative that improves on both.

While I don’t believe the ‘perfect’ IEM exists, and that everyone has their own preferences, I honestly struggled to find fault with Rn6 with my own music library and preferences.

ATOM Xs is not the most user-friendly system, and there’s been some concern about the modules’ durability, but nothing that FiR hasn’t publicly addressed and rectified. I can also nitpick about nozzles, safe tuning, or even pricing to some degree, but none of these are anything I’d consider a showstopper.

The only temper to my enthusiasm for Rn6 is that more people won’t get to enjoy it, since production is capped. I’d also like to see a permanent CIEM option, which would optimise the sound further and remove any issues with fit.


I do wonder, though, if the decision to limit its numbers is the idea that an IEM that does so much right without blowing people’s minds is bound to find limited commercial success, especially at this summit-level price tier. I also get that, for this sort of money, people want an IEM with a party trick or two that nothing else can do.

However, if you’re someone like me who strives to get as close to lifelike sound reproduction with a sprinkling of fun and excitement, not many IEMs that I know of do that quite as well and quite so effortlessly as FiR’s new Frontier.

It’s an IEM that can easily stand on its own as a premium one-and-done for most audiophile enthusiasts, and for that, it earns my highest possible recommendation.

This review first appeared on The Headphone List
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This iem just looks stunning! Damn it's practically jewelry...
I wonder if the Kinetic Bass does leak sound out of the IEM (e.g. like open headphones that may be be so wise to use at the office)?

Excellent review. As an owner this sums is up well. I find the staging with the red module one of the best in the industry, near perfect imaging, exceptional air and the sub bass seems seems to envelope the soundscape. I have not heard another IEM that can accomplish this. Is a sea of countless $3k+ flagships, Rn6 sets itself apart.


1000+ Head-Fier
The King Has Retuned
Pros: Excellent bass quantity/quality
Excellent mids
Excellent highs
Beautiful build quality
Great cable
swappable modules
Cons: Limited to 300 copies
Packaging/accessories could use some work
Understandably pricey
Rn6 Cable Front Back.JPG

Original Logo Small.png


Up for review today is the MUCH-revered FiR Radon 6 (Rn6) which I purchased at full price because of the kudos it was getting (and promptly threw up a little). FiR took the Xenon 6 (Xe6), kept the same drivers, retuned it, and fixed all of the complaints the Xe6 had. Now with lighter weight, a more durable finish, and an excellent cable, the Rn6 is ready to take on the current stable of TOTL IEMs for only $3,300 (yes, that’s still an exorbitant amount of money, but cheaper than almost every other TOTL IEM from the major market players). The Xe6 makes excellent use of its 1x Kinetic Bass 10mm Dynamic Driver, 2x OpenDriver Mid BA Driver, 1x OpenDriver High-Mid BA Driver, 1x OpenDriver High BA Driver (with Sound Reflector), and 1x OpenDriver Ultra-high Electrostatic Driver. It also has the ability to switch out ATOM XS modules to change the tuning and provide decibel reduction. Only 300 of these are being made…ever since it’s a 5-year anniversary model. It also still has the Xe6’s kinetic open bass port, albeit smaller in size – and it remains a tubeless design. Sweet. So how does it sound? Read on for the review.

Rn6 Case.JPG

Accessories/Earpads/Eartips (7/10):

Eesh, this is a tricky one. First off, it will take you probably 10 minutes to open the Rn6. Why? Because it has a sleeve on it that requires EXTREMELY careful removal and consistent shimmying to get it off the box. Five minutes later, once you get the sleeve off, there’s still a super tight box lid you have to remove from the box bottom – another five-minute process since it’s so tight. At last, you’re greeted by a FiR Space Force iron-on patch and the IEM itself with the cable attached. As I’ve learned on previous FiR IEMs, you will need to remove the foam that the IEMs are stuck into in order to remove them by pressing lightly from the bottom and slowly working them out from the top at the same time. If you don’t, you will bend the pins on your cable because the foam is TIGHT. Underneath the IEMs, you get a carrying case with a few random ear tips (like 5 sets) of various styles and types, none of which really make sense or lead to a good fit. As always, I'm using my Spinfit W1 tips since they're the best I've found (You can buy them here if you want a set:

Fir Rn6 Modules.jpg

You also get a cleaning tool and 4 ATOM XS modules – maybe. You might only get 3 – it depends on if FiR is feeling generous and is including the Red module still (there was a rumor that they were going to start charging for the Red module, but I haven’t seen that happen yet). The ATOM XS modules change the tuning of the IEM and can add more bass and let in more outside noise. I’ve included a chart showing the differences above – yeah, there’s not a ton of difference, but I can speak from experience that the Gold module increases the bass by quite a noticeable amount. So as usual, it’s something you can play around with and find your preference – some love the Red’s neutrality, some love the Gold’s bass, or something in between – find what works for you. Overall, this is about the bare minimum that packaging should come with. It could use more ear tips – I’ll be using my Spinfit W1s as usual. There’s also not a lot to make you feel special about spending $3.3k. Oh, and it comes with an empty box inside…not kidding. It’s just a spacer box – fill it with stickers and extra ear tips or something FiR! A plastic FiR bunny even, but clearly your box is too big for what you’re including. Also, get rid of the sleeve and print the model directly on the box – make it feel like a $3.3k product. Anyway, 7/10 here for not at least including several sizes of one type of ear tip – Unique Melody does a better job here – heck, TRUTHEAR’s $20 HOLA has more ear tips included. Weak.

Rn6 Cable connectors.JPG

Cable (9/10):

Man, I love this cable. I just want to buy this cable from FiR and use it on all of my IEMs. It removes all of the complaints I had about the Scorpion cable. It does seem related to the Code23 cable but supposedly has no relation at all. That said, it’s flexible, comfortable, not too heavy, only a little microphonic, and the pins feel sturdier than a normal cable. The duplex twist is immensely well done and gorgeous. The cable is also pure silver with a copper coating (the opposite of what you usually find on a silver-plated copper (SPC) cable. It’s a joy to use and feels almost as nice as the cable on the Ronin and Mezzo LE. The microphonics are my only real complaint here – tapping on the cable while music is playing sends loud reverb through the cable and moving your head side-to-side causes the same effect. Still, it scratches every other itch and still beats the Multiverse Mentor’s annoying paracord finish and the Trifecta’s ribbon cable, so 9/10 points here.

Rn6 Back.JPG

Build Quality/Comfort (10/10):

Excellent. The build quality here feels like a lesson learned from the Xe6. Since the Rn6 is very clearly related to the Xe6 in size, driver count, etc., it seems that FiR took the negative of the Xe6 (namely the fragile finish) and improved it with a rugged black aluminum build while retaining the sapphire glass faceplate with gold flakes. These appear significantly more durable and don’t pick up fingerprints like it’s going out of style. They definitely have a better build quality and feel than their direct competitor, the Campfire Audio Trifecta (also ~$3,300).

Additionally, since they’re made from aluminum, they are a little bit lighter than the Xe6 (we’re talking a very small amount with something this tiny – and the new cable adds some weight). Still, they sit in my ears more easily than the Xe6, which was a big complaint for the Xe6. The Rn6 is EXTREMELY small when looking at all of the other TOTL IEMs on the market these days. They actually fit inside the inner parts of your ear, unlike IEMs like the Ronin and Mentor which take up orbit around your head and create their own gravity field. They have a significantly better fit and feel than the Jewel as well, though they are competing directly with the Trifecta on size, as those are also very small and light – the Rn6 are a little thicker than the Trifecta and will stick out of your ears more. So, it’s 10/10 points here for build quality and comfort.

Rn6 Box.JPG


I’ve included quite a few TOTL IEMs on the below since I was lucky enough to hear all of these in a short period of time and some might be wondering which of these to choose from. Obviously, the Xe6 has the most bass, followed closely by the Rn6 and Trifecta, and lastly by the Jewel. Keep in mind that the Frequency Response Graph (FRG) can’t capture the kinetic bass the Rn6 and Xe6 have since that speaker is on the outside of the microphone – so those two are likely a little higher in the low-end. The mids among all 4 are all over the place with the Jewel showing the most pronounced mids and the Trifecta having the biggest dip. Lastly, the highs are all over the place with the FiR-io brothers being relatively flat and neutral while the Trifecta is skiing a black diamond and the Jewel drops the treble like it's hot. The songs below are designed to figure out what all of that means, so feel free to read all 4 reviews to see what the FRG can’t tell you.

Rn6 Trifecta Jewel.png

I am powering these, as usual, off of my HiBy RS8 with the A/B amp on medium gain at ~40/100 volume, so they’re nowhere near as efficient as the Trifectas are. I’m using the stock cable with a 4.4mm jack and Spinfit W1 ear tips (my favorite) through Tidal Hi-Fi with MQA and lossless files as well.

Lows (20/20):

I’m starting off with the Mid-bass/Sub-bass test I’m using David Guetta’s “I’m Good (Blue).” Holy crap, that’s some good bass. I can really feel the impact here (kinetic bass) without it having the extra unwanted reverb the Xe6 has. The sub-bass is intense here, and really good. This is truly the evolution of the Xe6’s bass – all of the quantity without the unwanted quality. The mids still manage to come through here quite clearly as well. It’s uncommon for me to have a DD on this song that avoids that Honda Civic with 10” subs rattle on this song – the Rn6 does that. 10/10 points.

Up next is Demon Hunter’s “I Am A Stone,” which I use to test whether the bass is too strong and overwhelms the mids as that is just as important as how strong/good the bass is. Typically, if the bass is excellent on the previous song, it’s overwhelming on this song – with only a few exceptions that have gotten good scores on both. The Rn6 is one of those IEMs. FiR managed to take the weakness of the Xe6 and turn it into a strength of the Rn6. By decreasing the size of the kinetic bass hole on the IEM, they’ve managed to keep most of the Xe6’s bass, but without it bleeding into the mids like the Xe6. What you end up with is a wonderfully bassy IEM that still has a good focus on the mids where they can be clearly heard despite the bass rumble. I don’t have a single complaint here, and the soundstage is excellent – this is about as perfect as lows can get – 10/10 points.

Mids (19/20):

Weaving The Fate’s “The Fall” is my test song for clean/dirty guitars and vocals with background instruments to see how clearly the vocals can be heard. Here is where we really begin to see how good the resolution and clarity of the Rn6 is. Not only are the intro clean guitars excellent, but the dirty guitars come in with all of the details you could possibly want – without losing the drums or cymbals – which are equally presented. The vocals of course sound great and have a nice forward focus, even during the chorus, which can easily get muddy on a lot of IEMs. Again, I can’t find a complaint with this song – 6/6 points.

Staind’s “Something to Remind You” has clean electric guitars and wonderful vocals – this song tests vocal quality and background noise. Wow, the bass guitar comes in nicely without blocking out the vocals – probably one of the few times I’ve ever heard separation and detail this good – ever. The Rn6 continues to amaze me with how it can introduce a high bass quantity without it overwhelming the mids or highs. Simply ethereal how it pulls this off. There is still the fingers-on-strings level of detail (without it being annoying) as well as a great focus on Aaron Lewis’s voice and all of the intricacies that entails. 7/7 points – just wow.

To test classical instruments in the mids, I’m using The Piano Guys' “Code Name Vivaldi.” Again, a ton of detail and an excellent balance are achieved here with this song. The cellos all come in cleanly, both the low and mid cellos. The piano can be heard quite clearly with full depth and body. The only thing missing here is a little of that emotional feeling that I want from this song that IEMs like the Trifecta can deliver. The Rn6 is like that 5-star restaurant dish that’s missing the soul your favorite local restaurant can put into their meals. I’m going with a 6/7 here because this song SHOULD be an emotional experience, not a technical experience.

Highs (18/20):

To test sibilance on headphones I use Panic! At The Disco’s “High Hopes.” Yep, there’s some sibilance here on the “S” sounds. That shouldn’t be surprising since almost every IEM has sibilance here if they want resolving highs at all. That said, it’s better than most (somehow) and earns the Rn6 a 4/6 on this song.

Dream Theater’s “The Alien,” is the highs test song I use to see if the cymbals/high-hats/snare drum can be clearly heard and distinguished from the rest of the music (also good for instrument separation.) The cymbals come through very clearly on these, again proving that FiR set out to deliver one of the most balanced IEMs I’ve heard – possibly ever. The snare drums and the high-hats come through cleanly and with even more detail than the Trifecta. It’s impressive how well they can be heard on an IEM with excellent mids and lows. I had to go back and forth a couple of times here between the Trifecta and the Rn6 to determine that the Rn6 somehow even beats the Trifecta’s highs in detail and clarity. 7/7 here – top-tier, and I’m absolutely gob-smacked.

Michelle McLaughlin’s “Across The Burren” is another of my favorite highs/sharpness test songs as it can easily sound painful on some headphones. FiR worked some voodoo magic on these IEMs. There’s no sharpness here somehow while having excellent highs and great mids and amazing lows. I don’t know how they pulled this off in a 6-driver IEM at a price lower than almost every other TOTL IEM. 7/7 points here.

Soundstage/Instrument Separation/Imaging (9/10):

I use MGMT’s “Time to Pretend” to test soundstage, instrument separation, and imaging. The imaging on these is great, the soundstage is great, and as already mentioned, the instrument separation is excellent as well. These IEMs continue to amaze me on their technical capabilities. Do they compete with the Multiverse Mentor here? Sure, it’s close enough that I can award the Rn6 a full 10 points without feeling any sort of discomfort. 10/10 points – the Rn6 deserves the praise it has received from countless people who have heard it.


OK, so here’s where it gets tricky. I’d say that the closest competitor here is the Trifecta, one of my favorite IEMs. The Xe6 is honestly a completely different IEM despite the DNA these two share – it’s got the wubwubwub and is a more emotional experience than the Rn6, but with terrible bass bleed into almost every other frequency band. The Jewel has less body and breadth, partly due to the decreased bass, but similar clarity and technical ability.

So really, it comes down to the Trifecta as the closest IEM to the Rn6. They both have good bass quantity, though the Rn6 wins for quality and avoids the bleed into the mids that the Trifecta got knocked for. Both have excellent mids, though the Trifecta has more “soul” than the Rn6 – that characteristic that you can’t quite put your finger on, but that makes it so you can FEEL the music better. That’s how I’d describe the Trifecta vs just about every IEM out there, and it’s the Trifecta’s main selling point. So while the Rn6 hits a LOT of the points you want from an IEM on the scorecard, the Trifecta will still make you feel the music better. That carries on to the highs as well - the Trifecta has some insane sibilance, which the Rn6 manages to tame a bit, and the Rn6’s highs are as good, or better than the Trifecta. The sibilance that both of these present also gives them some of the most resolving highs and damping that down can really ruin how they both present the music. So, for a more emotional experience, get the Trifecta. For better bass quality, less sibilance (but not none), and a more clinical experience – get the Rn6.

Rn6 Front.JPG


The Rn6 is a weird one for me. I was let down by its brother, the Xe6, on the scoring chart, but the Xe6 was also instantly super likable with casual listening. The Rn6 crushed the scoring chart, but didn’t have that immediately likable sound during casual listening that the Xe6 had. Going directly from the Trifecta to the Rn6 was a legitimate letdown. After giving the Rn6 some time to burn in, it’s a technically impressive IEM, but it is missing some of the soul that the Trifecta imparts. The Rn6 is still probably the most balanced IEM I have heard in a VERY long time with excellent bass, excellent mids, and great highs – that in itself is a massive accomplishment for FiR. I’m curious to see what they come out with next – maybe something that combined the excellent technicalities of the Rn6 and the emotional connection of the Xe6. That’s a really tough ask since those are really hard qualities to put your finger on. And yes, this is the first IEM to earn over a 90 on the v3 scoring chart - pretty sweet.

Headphone Scoring (v3):
Accessories / Earpads / Eartips (10 pts):
Cable (10 pts):
Build Quality/ Design / Comfort (10 pts):
Lows (20 pts):
Mids (20 pts):
Highs (20 pts):
Soundstage / Instrument Separation / Imaging (10 pts):
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This is why you have more than 1 iem 😉 one for the most hi fi experience you can get... and another to rattle your cavities out of your skull, tastefully.
Honestly? The gold module will do a pretty good job
I have the LX and Fir. I wanted to use the gold so bad, but the red is just amazing. No sense in trying to make it be something it's not, so I just swap IEM's when I want BASS. I love listening to the same content in different transducers 🙏🏼
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