Big, Balanced Bass | FiR Audio Radon 6 Review

Big, Balanced Bass | FiR Audio Radon 6 Review

While the company was founded five years ago in 2018, FiR Audio’s founders have been pushing innovations in the IEM market as part of 64 Audio for years. Their most recent innovation, Kinetic Bass, has been a major highlight of their Frontiers Series, and Radon 6 is the latest in the series, aiming to provide an engaging blend of accuracy and musicality that’s equally comfortable in the living room and on the stage. Is Kinetic Bass just a gimmick? Does Radon 6 offer more than just some fancy sounding tech for prospective buyers?

Build and Design

The basic design language of FiR Audio stands out from much of the IEM world, as rather than going with an acrylic molded shell, it uses an aluminum shell with clear 64 Audio roots, and spices it up a bit. The shell is lightweight and ergonomic, and I found it easy to get a good fit with a variety of eartips. The Radon 6 package includes a set of standard foam eartips and a set of Symbio Hybrid tips, which is basically like if someone stuffed a foam eartip inside of a silicone one. 

Radon 6 is a 6 driver tribrid – one dynamic, four open balanced armatures, and one EST. While the faceplate looks pretty typical, flip the IEM around, and you’ll notice that the dynamic driver has a unique venting system. The dynamic driver hits your ear directly adding to the physical sensation that accompanies good bass, and delivering a sound that’s somewhere in between typical dynamic presentation and bone conduction.

FiR Audio Radon 6 Review

FiR Audio has also developed their own pressure management system for IEMs called Atom. The version that Radon 6 uses is called Atom XS, and uses small modules that can be changed out using an allen wrench. There are four color-coded options: red is 10dB of isolation, black is 13dB, silver is 15dB, and gold is 17dB. While I found it difficult to actually see the differences in the aperture size for each module, I preferred the red, and I felt it provided the strongest sense of the openness and realism that are key characteristics of Radon 6.


It seems that lately there are basically just two different types of tunings: 1. Small variations on a common target curve (e.g. Harman Neutral or Diffuse Field), 2. Experimental tunings that excel at one thing in particular. Radon 6 largely falls into the first category, but there’s an experimental element to it as well, as FiR’s open Acoustics System and Kinetic Bass alter the sound experience while sticking close to a familiar, Harman-esque tuning.

Radon 6’s bass is one of the biggest highlights. The bass feels accurate, with strong texture and a great delivery of detail in low end instruments, but what really sets it apart is the Kinetic Bass system. It’s a simple idea – a dynamic driver with a large vent aimed directly at your earlobe – and the results are spectacular. Kinetic Bass offers a natural sense of impact, rumble, and depth to the bass without any need to exaggerate or over-emphasize the bass. So you get the best of both worlds: bass that is powerful and physical, but that also remains accurate and lifelike.

FiR Audio Radon 6 Review

The mids should be thankful for this bass innovation as it enables powerful midbass and subbass extension without needing to create the sort of bass shelf that overpowers the midrange. The mids offer strong detail, natural timbre, rich layering, and excellent vocal and instrumental delivery.

At the top, you get a treble which lends an open, airy feeling to the sound, with excellent definition and clarity, while avoiding fatigue. There’s a crispness to the highs as well, with an incredible sense of resolution. It seems like the more open nature of the design, with the Atom XS system and vented dynamic driver helps alleviate potential treble fatigue as well, allowing Radon 6 to deliver strong treble presence without feeling too bright or sharp.

While the balanced armature midrange and EST treble are well tuned, it really does seem like the key element that elevates Radon 6 from “really well tuned IEM” to “unique, exceptional flagship performance” is the Kinetic Bass. It’s not just about the bass performance itself, but the way that this sort of bass tuning makes room for the other positive aspects of Radon 6’s performance.

FiR Audio Radon 6 Review

The soundstage is another highlight here, and the width is exceptional, but it doesn’t offer quite as much depth as width. Likewise the imaging feels very strong left to right, and the overall imaging presentation is three dimensional and holographic, but the front to back imaging comes up just short in the depth. The Atom XS modules definitely have an impact here, as most of my impressions were gathered with the more open Red and Black modules, but Silver and Gold did seem to bring the width in a bit while adding to the depth.

To get some bass reference tracks, I turned to LoFi Girl’s “Study lofi” playlist, and found “Snowflakes” by Pandrezz. There were three main elements of the song that really stood out: the kick, the bass, and the muted snare. The kick has a low physical punch to it, while the snare hits up high, but evokes a similar physical reaction somewhere near the crossover of the highest open BA driver and EST. Radon 6’s Kinetic Bass gives the bass an incredibly deep, textured rumble that feels like it’s vibrating your entire skull. Sure there are melodic elements as well, and they’re nicely layered, adding width and depth to the sound, and Radon offers clear detail and a three dimensional feeling. Really though, we’re not on this playlist for the melodies. We’re here to get our ears pummeled by bass, and Radon 6 delivers quite the pummeling.

Often IEMs with excellent bass and some low end emphasis come up short when it comes to older recordings or classic rock, but this isn’t the case with Radon 6. From the vocal presentation, to the delicate piano, Radon 6 provides a lifelike delivery with an open, spacious feeling on David Bowie’s “Life on Mars.” There’s a great sense of the dynamics of the song as well, both in the presentation of the vocals and in the delivery of the band as a whole, building to the final chorus. The largely acoustic nature of the recording lets Radon 6 demonstrate its effectiveness for simpler instrumentations and natural sounds.

FiR Audio Radon 6 Review

Likewise, with a classical piece like the “Finale” of Stravinksy’s Firebird Suite, Radon 6 delivers rich details and character in each instrument, with textured bowing in the strings, and the fast stabs of the brass. The bass gets to flex its muscles in the powerful slam of the timpani in the climax of the piece, with Radon 6 giving an incredible display of dynamic range, along with incredible coherence and cohesion as each piece of the band has a clear sense of separation while feeling like a united whole.

Comparison: Campfire Audio Trifecta, Empire Ears x Astell&Kern Odyssey

Seeing how the technology underlying Radon 6’s bass performance is a key aspect of its sound, I wanted to compare with other IEMs that have offered some degree of innovative design or low end delivery. To accomplish this we brought in the Campfire Audio Trifecta, famed for its triple dynamic driver configuration, and the Empire Ears x Astell&Kern Odyssey, which uses a bone conduction driver for bass, and offers a tuning that’s not too different from Radon 6 overall.

FiR Audio Radon 6 Review

In the overall tuning, Trifecta is clearly aiming for a bit more warmth than the other two. Odyssey really has a big “wow” factor, with just that extra bit of sizzle, and a more vivid overall presentation, while Radon 6 feels a bit more natural, with less obvious sense of deliberate emphasis in certain ranges. 

All three have some unique soundstage and imaging characteristics. Trifecta has an absolutely huge soundstage, and an imaging presentation that feels very over-ear headphones. Radon 6 gains some extra width and air from its more open design, but doesn’t provide the same level of spatial sensation as Trifecta. Odyssey feels the most like it’s just a really great IEM soundstage, with good width and depth and strong imaging, but nothing that stands out in particular, or at least not that stands out the same way that Trifecta and Radon 6 do.

In the bass, Radon 6 hits somewhere in between the two. Where Trifecta has a bigger, rounder midbass and Odyssey has a mix of punch and deep rumble, Radon 6 is neither as round and warm as Trifecta, nor quite as emphasized into the subbass as Odyssey. Trifecta definitely flirts with bloat a bit more than the other two, but Odyssey’s bass can also bleed up a bit too, with Radon 6 having the most controlled bass of the three.

FiR Audio Radon 6 Review

As you delve deeper into the subbass, there’s an almost unreal sense to the depths that Odyssey can plumb. Radon 6 has some strong low bass sensation, but without the extreme depth. There is a slightly stronger sense of texture in Radon 6 that makes some low bass instruments feel alive, and the specific way it delivers the low bass through the Kinetic Bass port gives me a feeling all around the back of my head, while Odyssey’s powerful subbass feels more localized.

When you put it all together, Radon 6 really falls in the middle: Odyssey provides the most vivid, exciting sound, and Trifecta is warmer with a more relaxed overall presentation. Radon 6 offers a more natural sound that’s more organic than Odyssey, but without moving into the lush, warm territory of Trifecta, and is more technical than Trifecta, without quite matching the insane prowess of Odyssey.

The Bottom Line

As a relatively new brand building premium, flagship level IEMs, FiR Audio needs to not just build a great product, but also provide some sort of differentiation that helps them stand out in an increasingly competitive market. WIth Radon 6 – and the Frontiers Series as a whole – FiR Audio delivers not just excellent sound, but also a true innovation in the Kinetic Bass system.  The combination of a great tuning and design, and a new elevation of the IEM listening experience with Kinetic Bass, Radon 6 is a clear standout in today’s flagship IEM market.