Home » THL Recommends » In-Ear Monitors (Universal-Fit) » FiR Audio Radon 6: A New Frontier

FiR Audio Radon 6: A New Frontier

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. 

Continue to Radon and Xenon…



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.


Leave a Reply

Your email address will not be published. Required fields are marked *

Recent posts