FIR RADON 6: Conceptualization the boundaries of sound

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 





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.




Sound, tuning, convenience, design, build quality and materials



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