FiR Audio Frontier Series (XE6, KR5, NE4) Introduction and Comparison.

Sound Analysis.

I tested and analyzed XE6, KR5, and NE4 sound performance paired up with a neutral LPGT source while playing a variety of test tracks, such as Agnes Obel “The curse”, Sandro Cavazza “So much better” (Avicii remix), C-Bool “Never go away”, Ed Sheeran “Shape of you”, Alan Walker “Darkside”, Galantis “Hunter”, Iggy Azalea “Black widow”, Indila “Boite en argent”, Dua Lipa “Love again”, Counting Crows “Big yellow taxi”, Bob Marley “Jamming”, David Elias “Vision of her”, and Michael Jackson “Dirty Diana”.  All 3 pairs arrived to me already burned in, with over 50hrs on each.  Also, I was using Xelastec eartips for a better isolation and a more secure fit in my ears.

First of all, let me start by making a general comment about the bass.  I found the Kinetic bass to trigger a very different ear sensation, like a pair of sub-woofers over your ears pumping the air, simultaneously making you hear and feel the bass without any pressure inside your earcanal.  It’s not a gimmick, and this sensation makes you feel like being in a room with sub-woofers surrounding you.  The bass has a textured rumble, deep extension, and a noticeable weight with a powerful slam.

Another thing to note, as I already mentioned, the ported Kinetic driver opening of XE6 is bigger which also relates to its bigger bass impact.  And, you do need to pick a pair of eartips that will give you a more secure fit, the reason I’m using Azla Xelastec and Crystal tips.  Otherwise, under the shell weight, especially with heavier SS XE6, there will be a bigger gap and more sound leakage.  Yes, each of the Frontier Series IEMs has some sound leakage because you are dealing with an open driver.  I suspect, CIEM will have less sound leakage due to a custom fit which can also affect the bass response.

Below is my detailed analysis of each pair of IEMs as I hear it.  I also tested 3 pairs of included Atom XS modules to share how they affect the sound tuning and which one I preferred in each pair up.


XE6 has a fuller body sound with a natural detailed tonality.  The sound signature is closer to L-shaped, probably better described as a reversed J-shaped since its elevated bass doesn’t exactly overpowers the upper mids and treble, giving them room to breathe, though bass still dominates the tuning and more forward in presentation.  With a deep, textured sub-bass extension and rounded slower speed mid bass impact, the warmth of the analog bass texture extends over a fuller body lower mids, making a seamless transition without muddying the sound.  Mids/vocals are smooth, warm, laidback (not as forward), organic, with a good clarity and natural retrieval of details.  Treble is also smooth, though still well defined and also with a natural level of clarity.  When you start listening to XE6 and hear its bass and smooth organic tonality, you almost expect the sound to be thick, dense, less detailed, and not as coherent.  But it proves you wrong, especially when you hear vocals and non-synthesized instruments.

Soundstage is wide open, literally making you feel like listening to open back headphones.  The layering and separation of the sound is not on the highest level, these IEMs are not intended for critical micro-detailed listening.  XE6 has a pure analog open sound, big speaker like visceral bass, smooth organic clear vocals, and natural detailed treble extension.  But what surprised me the most was the natural coherency of DD/BA/EST tuning.

Atom XS comparison w/XE6:

  • gold – deep powerful bass, natural warm thicker vocals, natural clear treble.
  • silver – the same powerful deep bass, natural warm vocals with a little more clarity, and a touch more sparkle in treble.
  • black – deep powerful bass which is a little lower in sub-bass quantity relative to golden/silver, natural warm thicker vocals that are a little more forward due to bass being a touch less intense, and treble which is closer to silver, being natural clear with a touch more sparkle.

Silver Atom XS was my favorite module with XE6.

vs FiR Audio M5 – M5 bass has less mid-bass weight and not as deep sub-bass.  M5 bass is more articulate, faster, and less analog in comparison to a more powerful and more analog impact of XE6 bass.  Also, M5 mids have less body, and sound more revealing and more detailed in comparison to warmer, thicker, more analog mids/vocals of XE6.  Also, M5 treble has more sparkle and air.  In general, these are two differently tuned IEMs.



KR5 has a more balanced W-shaped sound signature with a natural revealing tonality.  Powerful articulate bass with a deep elevated sub-bass extension, fast punchy mid-bass impact; overall, a layered powerful bass that has weight and impact of analog dynamic driver and a speed and accuracy of faster BA bass, faster than XE6.  Mids are detailed, layered, natural, more forward, with just enough body and natural micro-details without getting too analytical or sterile.  Treble is crisp and clear, well extended, packing extra energy without being sibilant or harsh.  It does add more clarity to the sound, thanks to the mid-treble boost.  The overall sound is more energetic, more forward, brighter, still analog, but with higher level of detail extraction and a lot crisper treble relative to XE6.

The soundstage is very big.  While the sound is as open and expanded as XE6, due to a brighter and more revealing tonality without a thicker bass, the sound opens up even more, with a huge expansion in all 3 dimensions, reaching holographic level and nearly 3D imaging.  Layering and separation of the sound is on a high level as well, part of a more revealing nature of the tuning.

Atom XS comparison w/KR5:

  • gold – powerful articulate bass, natural revealing mids with a good extraction of details, crisp airy treble.  3D holographic soundstage
  • silver – bass has a little less weight, especially not as deep sub-bass, mids/vocals sound a little brighter and more forward, and treble has more sparkle.
  • black – bass remains the same as with silver, but perception of mids is a touch more elevated and slightly more forward.  Treble is the same as in silver.

Gold Atom XS was my favorite module with KR5.

vs Fir Audio M5 – here the comparison is closer, and some will probably find KR5 to be an upgrade to M5.  Right away you will notice a bigger and more holographic soundstage expansion.  M5 soundstage is big, but switching to KR5 feels like you are wearing open back headphones.  Bass is noticeably bigger and bolder as well, with more weight and deeper extension of sub-bass and more powerful impact of mid-bass.  The soundstage and the bass are the two most noticeable changes.  Upper mids and treble between these two are quite similar.



NE4 has a balanced W-shaped sound signature with a natural detailed tonality and a more relaxed presentation of the sound.  In a way, tonality of NE4 felt like a scaled down crossover between XE6 and KR5 because it does have a smooth natural tuning leaning toward XE6, but not as warm or with the same powerful bass impact as XE6.  And it is detailed and less colored like KR5, but not as revealing, resolving, or layered as KR5.  Also, the soundstage is wide, but not as wide as KR5, more like XE6.  The bass is very powerful, with a deep sub-bass that has more mid-bass impact, actually, a very strong mid-bass punch.  Lower mids are a little north of neutral, with a bit of an extra weight which gives the sound plenty of natural body, while upper mids are being clear, detailed, natural, a little smoother and not as layered or micro-detailed.  Vocals have a natural detailed clarity, on a smoother side and with more laidback presentation.  Treble is a bit reserved.  Treble is clear and has a good natural definition, but not as much sparkle or air as KR5, more like XE6, maybe even a little smoother.  As a result of this tuning, NE4 brings more focus and natural organic details to the mids and vocals.

The soundstage is wide open, similar to XE6, and not as holographic as KR5.  I think the smoother details of the sound and stronger mid-bass keeps the soundstage within a natural expansion boundary, less exaggerated and not as 3D.  The layering and separation are just OK, not on the same level as KR5, but similar to XE6; NE4 is also not tuned for a critical listening.  The sound is not congested or veiled, everything is nicely separated and easy to pin point in the mix.  Just that due to a lack of extra air in treble, I sense less “air” between the layers of the sound.  This does improve as you step through Atom XS modules, especially with black module, but it doesn’t reach the same level as KR5.

Atom XS comparison w/NE4:

  • gold – balanced sound sig with a natural clear tonality, powerful bass with more mid-bass impact, clear natural mids/vocals, and clear natural treble.
  • silver – still the same balanced sound sig, but mid-bass impact is a bit leveled off which gives mids a little more room to breathe with slightly more forward presentation and a touch more crunch in treble.  But the most noticeable change here was wider soundstage.
  • black – a refinement of “silver” tuning with mids being as forward yet more detailed and with a better layering and separation of the sound, and with treble having a more noticeable improvement in retrieval of details and airiness.  The sound has a wider soundstage, similar to silver module, and due to the improvement in treble and mids, the separation and layering is better which results in improvement of vertical sound dynamics, making the sound to be less compressed and more expanded.

Black Atom XS was my favorite module with NE4.

vs Fir Audio M5 – here, the difference is quite noticeable, not too many similarities.  M5 does have a wider soundstage due to its more revealing and airier sound.  The bass of NE4 has more weight with a deeper sub-bass and bigger mid-bass punch.  The mids of M5 are more revealing, less colored, more micro-detailed, while NE4 is smoother, more natural, with fuller body.  And M5 treble is brighter, crisper, and airier, while NE4 treble is smoother and more reserved.



When it comes to IEMs, it is not easy to reinvent the wheel.  Still, some manufacturers do try in order to stand out from the crowd, but not too many can come up with something more original.  In my opinion, FiR Audio actually succeeded in making that happen because I don’t recall seeing any other open back bass driver design until now.  And, it is not just a visual eye candy or a marketing gimmick.  It does work as advertised where you both hear and feel the bass, and integrates nicely with 3 different FiR Audio IEM models, complimenting each one’s original sound tuning.

Based on my testing, out of XE6, KR5, and NE4, I found XE6 to have the warmest tonality with bigger bass impact and thicker fuller body analog sound tuning.  KR5 is the most revealing with the fastest bass, more detailed and less colored mids, and crisper treble, as well as having a wider soundstage.  NE4 takes from both of these IEMs, with a bass that not as elevated as XE6, but still having a strong mid-bass impact, not as thick lower mids as XE6, but still with fuller body than KR5, and with the smoothest less extended treble which puts more focus on organic natural vocals.

I’m looking forward to spend more time with these, probably focusing next on XE6 in a more detailed write up and comparisons when I receive the official review sample.

4 thoughts on “FiR Audio Frontier Series (XE6, KR5, NE4) Introduction and Comparison.

  1. Out of these 3 FiR Audio IEMs, which one do you prefer? To me, it would be the KR5 w/ Silver Atom XS because it seems to be the least colored IEM.


    1. Quite a few people mentioned to me that since they want less colored, more transparent tuning, KR5 would be the way to go, as an upgrade to M5. I prefer XE6 because it offers something different to complement the rest of the IEMs I have and use daily, but some might find it on a warmer and a smoother side of their preference.

      Liked by 1 person

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