FiR Audio Neon 4

General Information

The Neon 4 is for the lover of smooth, creamy sounds. Which it achieves without sacrificing resolution. The Neon 4’s highlight lies in its lush, upper mids and trebles. As well as a stellar sense of space and positioning from its ATOM XS module. Place these characteristics on a snappy, speedy bass foundation for an immersive, detail-oriented listen.

The Custom-fit IEM comes in a durable acrylic, with an array of elegant color and design options. The Universal-fit version features a machined aluminum shell and gorgeous sapphire crystal glass faceplates.

The Neon 4 is equipped with 3 balanced armature drivers, a 10mm dynamic driver for lows, fed through the Kinetic Bass port.

Along with the rest of the Frontier Series, the Neon 4 comes in a Universal-Fit and a Custom-Fit version.

USD 2299


1x 10mm Kinetic Bass Dynamic Driver
1x OpenDriver Balanced Armature Driver for mids
1x OpenDriver Balanced Armature Driver for high-mids
1x OpenDriver Balanced Armature Driver for highs (with Sound Reflector)

Freq. Range: 20-20kHz
Impedance: 22ohms

Machined Aluminum Shells (UIEM)
Sapphire Glass Faceplates (UIEM)
ATOM XS Interchangeable Modules (UIEM)
Leather Protective Case (Audiophiles)
ree Custom Artwork & Premium Faceplates (CIEM)
Internal ATOM and ATOM X Modules (CIEM)
Aluminum Protective Case (Musicians)

Latest reviews


100+ Head-Fier
Middle Child Syndrome
Pros: Tremendous bass reproduction
Smooth and easy listen
Cons: Vocals feel extremely recessed
Veiled and dark sound signature
Treble is lacking



Thank you to @Damz87, MiniDisc Australia ( and Fir Audio themselves for arranging this Australian tour of the Fir Audio RN6, XE6 and NE4.

As the beneficiary of a trio of Fir Audio IEMs as part of the Australian tour, I was conversing with the previous reviewer and hearing some of his thoughts regarding this lineup of IEMs. One of the comments that I had found myself making was that the Neon 4 was the red-headed stepchild of this family. Being the least expensive out of the Radon and the Xenon, my expectations inevitably led to the idea that this would be the least amazing out of these three rather expensive IEMs. However, this remains a review, and I endeavoured to shed my preconceptions in order to make a determination as to whether the Neon 4 deserves your well-earned dollar, or is even something worth looking at. And so, would the Neon 4 end up being that forgotten child or perhaps the golden child?

The Factual Stuff

The Neon adopts a 4-driver setup with a “Kinetic Bass” 10mm dynamic driver coupled with three balanced armature drivers. These are housed within a machined aluminium shell that has been polished to a very handsome sheen and combined with a sapphire glass faceplate.

The review tour Neon came with a handsome leather case, a variety of eartips, ATOM modules which provides the end-user with the ability to alter the pressure relief system and a cleaning brush.

What are ATOM modules? Well the RN6 features a pressure relief system that utilises a number of modules to alter the amount of noise isolation and therefore impacts the sound signature of the RN6. The modules are:
  • Gold = 17dB isolation;
  • Silver = 15db;
  • Black = 13dB; and
  • Red = 10dB.
The included cable is 8 wire, finished in black and terminated in 4.4mm. There is no apparent information relating to its materials and other specifications.

The Opinion Stuff​


The following review was largely conducted using the silver module


The Neon 4 provides a rather healthy bass boost that provides a distinctly punchy and impactful sub and mid-bass response. The Kinetic Bass driver relates to the open setup of the driver, pushing sound directly into your ear. The result is a physical sense of bass that is unlike any other IEM in the market, with the exception perhaps, of those utilising bone conduction drivers.

“THE PLAN” from the TENET soundtrack has an ever-present bassline that extends deep and hits rather hard, the Neon reproduces this bass with much gusto. The sub-bass extension and boost presents itself in a wholly engaging and physical manner.

“Second Life” by Slander is a bombastic EDM track with very prominent mid-bass. The Neon generates a physical punchiness to the mid-bass in this song that is almost harrowing. The pressure exerted and the prominence of the mid-bass provides a significant sense of drama that is wholly addicting.

The quantity of bass is one thing and in this regard the Neon delivers in spades, however what about the quality? The Neon reproduces these bass frequencies with significant speed and preciseness that almost makes you forget about the generous amount of boost that Fir has achieved when tuning these IEMs. The bass can present itself as potentially boomy at times, but this does not arise in a manner that distorts itself into being an ear-bleeding experience. It remains detailed, textured and readily dissectible instead of being an indiscernible mess. Out of curiosity, I added even more bass via my Chord Mojo 2 and the result was hugely impressive. The DD managed to maintain its composure and reproduce bass in a detailed manner with little to no distortion. This was definitely not an EQ profile that would be listened to on a regular basis but rather a demonstration of the technical prowess of this DD and the seemingly endless pile of bass from which it could draw upon.

Overall, the bass on the Neon is definitely the most prominent aspect of this IEM. It imbues a tremendous sense of physicality that forces you to be engaged with the music. There is a sense of warming up the entirety of the frequency response curve and thus this is hardly an IEM for acoustically focused music but the sheer novelty of the bass is something to behold.


The folly of the Neon (and perhaps the Radon and the Xenon) is that the glorious bass comes at a cost. The midrange of the Neon sits behind the that generous mid-bass bump leading to some recessed vocals. This is most prevalent with songs with male vocals and hip-hop such as “Ballin’” by DJ Mustard & Roddy Rich. It feels as though you are seated in front a drum set with the rapper sitting behind it. Even in less aggressively produced basslines such as Bruno Mars’ “24K Magic” presents the same issue. There is a veil going on here and the staging of the songs become rather odd in their presentation.

Moving on to female vocals, “Billie Bossa Nova” by Billie Eilish provides a warmed mid-section but higher register female vocals do not suffer the same fate as males. Whilst not forward in the presentation, it is distinctly not as veiled as the aforementioned songs. In terms of instrumentation, the Neons do not do anything that could be construed as “neutral”. “Tank!” by the Seatbelts has a gorgeous mix of instruments and the reproduction of these by the Neon leaves me wanting. The trumpets, the cello and the bongos seem to be resonating from one singular location and lacking any sense of uniqueness in their reproduction.

Perhaps the only potential benefit I could give to the Neon is its rather smooth reproduction of the mids, there is not sense of shoutiness or sibilance from upper register vocals.

Overall, there is a distinct sense of loss in the mids compared to the Radon and the Xenon which manage to balance their coloured tuning well. The Neon, despite having somewhat less bass than its two cousins presents a distinct veil that is quite unforgiving to the midrange.


Moving to the upper ends of the frequency response, the treble region on the Neon is rather smoothed out. “Reckoner” by Radiohead is a distinct song by virtue of its constant percussion which on a brighter IEM has a sense of sparkle. The Neon, provides a minor sense of tingliness when these percussions hit but over the result is rather underwhelming.

“You & Me (Remix)” by Disclosure/Flume is a favourite test track of mine due to the rather disorientating synth in the chorus that seems to tickle the eardrums with a rather good treble tune and seems to gouge out the eardrums with a bright IEM. The Neon did none of these things and the synth seemed to come and go without an afterthought.

However, moving away from these specific tests to really wring out an obvious sense of sparkle, the treble remains distinctly smooth and rather easy going. Over the course of several hours of listening, the NE4 remained restrained enough to not generate any fatigue. The NE4 is more akin to the XE6 in its treble tuning compared to the RN6 but ultimately it is even more limited in this respect. Whilst it was perfect for a relaxing listen to tunes for hours on end there was a loss of engagement in my experience and the prevailing sense that this is a dark IEM and that it doesn’t seek to excite but rather lull you into a comfortable listening experience.


The aforementioned tuning profile of the Neon lends itself to diminished technical performance. And whilst I believe tuning is not the be-all end-all of a IEM’s ability to resolve, image and separate music on a grand stage, it is rather critical portion of making these abilities abundantly obvious. On the Neon, I believe that these are rather good in terms of their resolution and ability to produce microdetails, it simply requires a far more critical listen to discern these features. “Rush Over Me (Acoustic)” Haliene provides an extremely well recorded vocal line and a very raw pianist recording, wherein creaks, pushes of the pedal and fingers glancing over the keys becomes rather present in the mix with highly resolving and well tuned IEMs. These details are still present with the Neon but unlike say, the MEST MK3, these details are not very clear.

In terms of imaging, I pulled out Precogvisions favourite “Fine” by Taeyeon with its overlaid vocal lines in the bridge. The result with the Neon is a clear discernment of different vocal lines but the ability to image them precisely is rather muddied.

Soundstaging is a rather divisive aspect of IEMs considering the IE part of IEMs. However, there are some gems out there that seem to present an out-of-head experience. The Neons staging capabilities are rather excellent, with songs such as “One-Winged Angel” by Nobuo Uematsu presenting in a rather grand manner. The stage is nicely wide and there is a sense of ‘faux’ depth which I say due to the rather recessed nature of the mids.

Dyanmic swings with the Neon are rather spectacular with the same song presenting in a bombastic nature that is almost harrowing to listen to. Swings in volume, both macro and micro seem to jump out you.


The Neon is a strange beast, the bass is reigned in from its cousins but so too are the mids and treble. The result is a rather dark sounding IEM that suffers from a loss of perceived detail, sparkle and engagement with vocals and certain instrumentalization. It is helped by its technical performance and its highly addictive bass, but alas, is not saved by it.

Treble sensitive individuals, or those looking for one of the bass experiences at this price should look to the Neon 4 but should understand its caveats.


One thought coming to my mind here namely lessons learnt after multiple DAPs, DACs and Amps plus headphones and IEMs is synergy! Hoping for the one and only holy grail Setup is maybe just a nice wish unless buying according synergy transducers and I don't believe even the best sources are an exception here. There's a reason why people are having multiple devices in parallel or reducing inventory and keeping only the ones with right synergy.

Shanling M6 Ultra

I would characterise the M6 Ultra (M6U) as a smooth, slightly warm source with an increased sense of presence in the mids and a strong note weight.

The Neon and the M6U do not really play nice with the increased warmth and note weight muddying things up further with the Neon. The M6U seems to heighten the already dark sound signature of the Neon and moves it into muddiness. Perhaps more suited for the enjoyer of much darker sound signatures, the M6U seemed to turn the Neon into what I have termed the LCD-2C of IEMs. I would now like to note that I did not enjoy the LCD-2C for sounding as if there was a cushion over the driver.

I would give this combo a miss unless you really need nothing but bass.

Chord Mojo 2

I would characterise the Mojo 2 as a very, very slightly warm neutral tonality with a more natural reproduction of instruments and voices with no DSP enabled.

This was a far better combo that the M6U especially with the bonus of DSP functionality. This is where the Neon became much more enjoyable to me as I turned up the mids and treble and reign in the bass to present a more neutral picture. This really revealed to me that the Neon was not in my wheelhouse. With no DSP, it presented a rather decent reproduction of music but in my opinion was still do dark for my tastes.

I would recommend this purely based off DSP functions.


vs RN6 and XE6​

Yes, yes. I understand that these two older cousins are far more expensive than the Neon but it remains to be said that the leap between the Neon and the RN6/XE6 is absolutely night and day. Whilst all three take a very unique approach to tuning with slight variations, the RN6 and XE6 both work "in spite" of such a tuning. They remain technically proficient in the face of a rather coloured tuning profile that is unlike a lot of IEMs in the market where as the Neon seems to simply miss the mark. The RN6 takes a more airy approach in the upper mids and treble creating a sense of space. The XE6, whilst more confined than the RN6 presents music with a certain bombastic excitement. And then the Neon provides the experience of listening to a drum set with a whole bunch of vocalists and instruments behind it.

Putting aside price, which is not exactly fair, both the RN6 and XE6 blow the Neon out of the water for me.

vs MEST MK3​

(noting that this is off memory and notes)
The MEST MK3 whilst have what I would term a 'warmed' sound signature remains much more neutral than the Neon 4. Apart from this, the MK3 manages to present music in a much more balanced manner. Mids are more forward in the mix compared to the Neon, the treble is executed far better and the technicalities of the MK3 simply beyond reproach. With greater perceived resolution and imaging capabilities, the MK3 presents a much more enjoyable experience both in terms of tonality and sheer resolution.

Considering the closeness of price here, I would go with the MK3 all day.

Quality of Life & Value

The Neon like the XE6 and RN6 is a rather angular shell that is quite deep, posing an issue for smaller ears. Thankfully the shell is some form of polished aluminium and is far lighter than the XE6.

The various atom modules provide you with the ability to alter the level of isolation of the XE6 which is vented, whilst altering the tuning.

For 2299 USD, I cannot really justify the Neon's pricetag when compared to a number of options both below and at the same price point. I do not believe that the Neon, apart from potentially the sheer power of the 10mm DD has anything to offer up against its competitors in this price bracket.


The Neon 4 is the most 'sensible' of the FIr Audio IEMs that I have tried. However, in being sensible (ie smoothing things out and playing it more safe) it seems to lose a certain je ne sais quoi that was present in its older (and much more expensive) cousins. Overly dark with a recessed midrange and without leaning into the same level of tremendous amounts of bass as its more expensive cousins, the Neon 4 doesn’t stand out in any regard.

It remains competent, technically proficient and a rather easy listen but there is not much to dissect with its rather unsophisticated listening experience. In providing a taste of the what the Fir Audio TOTLs have to offer, the Neon seems more like a stepping stone rather than just a good IEM. For the price, I would probably go with a MEST MK3.



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