FiR Audio Radon 6 (Rn6)

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.

FIRST IMPRESSIONS: 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: https://audiotiers.com/tour-fir-audio-gen2-frontier-series-ciem-lineup-xenon-6-krypton-5-neon-4/.

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 AudioTiers.com and follow the instructions in the “Getting Started” box on the Tours page: https://audiotiers.com/tours/.



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: https://www.firaudio.com.



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.



Configuration

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.

Fit

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: https://audiotiers.com/reviews-fir-...e-that-adds-a-new-tactile-dimension-to-sound/

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.

Preamble​

Thank you to @Damz87, MiniDisc Australia (http://minidisc.com.au) 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​

Sound​

The following review was largely conducted using the silver module

Bass:​

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.

Mids:​

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:​

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.

Technicalities:​

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.

Synergy:​

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.

Comparison​

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.

Value​

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.

Conclusion​

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.

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


Specifications
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 firaudio.com, 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 firaudio.com 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.