FiR Audio Radon 6: A New Frontier

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. 

Continue to ATOMic tuning…



Picture of Guy Lerner

Guy Lerner

An avid photographer and writer 'in real life', Guy's passion for music and technology created the perfect storm for his love of portable audio. When he's not playing with the latest and greatest head-fi gear, he prefers to spend time away from the hobby with his two (almost) grown kids and wife in the breathtaking city of Cape Town, and traveling around his native South Africa.


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