I’d like to extend a special thanks to Bogdan Belonozhko and his incredible team at FIR Audio for their continued support, enthusiasm and insight, without whom this and so many other reviews would not have been possible.
Space…the final frontier. Those four simple words, made famous in the opening credits to one of my all-time favourite TV shows, Star Trek, literally sparked my love for all things fantastical, technological and adventurous from a very young age.
This same spirit epitomises what FIR Audio set out to do almost three years ago now, with the debut of its Frontier Series IEMs: Ne4, Kr5 and Xe6. Since then, Rn6, a fourth Frontier derived from Xe6 as a neutral(ish)-tuned counter to its co-flagship’s thick warmth, completed the set, which raised the bar – in my opinion – for every other IEM competing in the increasingly-crowded $3,000+ ultra-high-end IEM market.
What sets the Frontiers apart from many of its competitors, however, is FIR’s expertise in designing, making and maintaining custom IEMs for the professional audio industry – some of the world’s foremost musicians, touring and mastering/recording engineers. The same resources are available to audiophile customers wanting custom creations of their own.
While the custom IEM option is certainly not unique to FIR, what makes FIR’s customs special, particularly when it comes to the Frontier series, is that design innovations like Kinetic Bass and ATOM venting seem to be optimised for custom shells, elevating what are already high-performance IEMs even higher.
In this review, which should ideally be read partly as an addendum to my full Xe6 and Rn6 reviews, I’ll cover some of the benefits (and potential pitfalls) of switching from universal to custom Frontiers, while also exploring FIR’s latest-and-greatest custom IEM innovation: full metal shells.
Recap: the FIR flagships
Since the Frontiers aren’t exactly new anymore, I expect many of you would have either heard of, heard, or owned/own a pair, and so just want to get to the meat of whatever it is I’m attempting to write here.
Still, it’s probably a good idea, to set the context, to recap the highlights of the Frontier flagships, Xe6 and Rn6, just so that we’re all on the same page when I start discussing the changes I hear when going custom with each of them.
Xenon 6
In three short years, Xe6 has become one of the most popular high-end flagship IEMs, which, given its unapologetically warm, thick and full tuning, is quite remarkable. The ‘party trick’ here is how this IEM defies conventions by exposing top-tier technical performance despite the warm wall of sound, like an orchestra playing in pristine detail and space inside a smokey auditorium.
There are reasons for this, of course, not least being FIR’s Kinetic Bass driver – an open chamber exposing the bass dynamic driver through pseudo ‘bone conduction’, in combination with an array of open BA drivers for bass through treble, capped off with an electrostat driver for upper treble air.
All of these drivers interplay with FIR’s open acoustic structure to deliver one of the most unique sounds of any IEM, which can then be further shaped by the chain (cables and sources), and fine-tuned with a set of four ATOM modules that attenuate bass and treble in different measures.
In my full Xe6 review, I describe Xe6’s alluring sound profile thus:
It’s hard for me to sum up Xe6’s tonality like I would most other IEMs. Is it a U or a W, for example? Depends on the track, sometimes it’s both. It can also be a V, with the mids taking a back seat, and it can be a reverse J, with everything subservient to the bass and lower mids with a touch of added air up top. Tonally, Xe6 is like a chameleon, and although warm, thick and bassy are a given, they’re not always going to define what you actually hear once the music starts to play.
Radon 6
A surprise ‘spinoff’ from Xe6, Rn6 was only revealed months after Xe6 was already established, and then only in limited quantities, with the same driver configuration and overall design as Xe6 but with a markedly different tuning direction. Gone is the thickness and warmth, replaced by a sometimes-cutting clarity that somehow stays on the right side of ‘natural’.
Despite its equally-impressive tonal and technical performance, Radon’s ‘Achille’s Heel’ was and remains its proximity to Xe6. Those coming down on it the hardest seem to harp on about how ‘normal’ it sounds compared to its distinctively-coloured brother, and that this ‘failure to be different’ is a mark against any IEM with a multi-kilobuck asking price.
Of course there’s always the flipside, with those turned off by Xe6’s midbass and lower midrange ‘blanket’ praising Rn6 for its clarity, refinement and true-to-life sound. To me, it’s an IEM that retains a blush of colour while bringing the Frontier sound about as close to neutral as we’re likely to get from FIR, which I describe as such:
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 ATOM module.
Two sides of the same coin?
Even today, I read debates about whether Xe6 and Rn6 are simply two sides of the same coin, or whether they are, in fact, two distinct, unique IEMs. I tend towards the latter, choosing Xe6 for a ‘flavour’ that doesn’t always work perfectly for everything, but still sounds amazing with most music, if you know what I mean.
Rn6, on the other hand, is an IEM I can trust to present almost any music in an engaging, accurate and refined way, especially now that I’ve fine-tuned its performance with upstream additions like PW Audio’s majestic Orpheus Shielding cable (Xe6, meanwhile, is permanently tethered to Eletech’s sublime Ode to Laura).
Tweaks aside, the Frontier flagships still represent the high-water mark for FIR Audio, and are, in my opinion, as relevant today as they were on release day. But that’s not the whole story, because both of these IEMs are also made in two different guises, and it’s only when I switched from the universal versions to customs that I discovered just how groundbreaking they both really are.
Continue to Customising Frontiers…
