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FiR Audio Frontier Series NE4 – NEON 4 IEMs – Exceeding All Expectations

FiR Audio Frontier Series NE4 – NEON 4 IEMs – Exceeding All Expectations

FiR Audio NE4 IEMs are a pair of Universal IEMs that can also be bought as customs, priced at 2299 USD, and designed with a superb sonic quality for both musicians and audiophiles. They aren’t the priciest IEMS I review on Audiophile-Heaven, by a good margin actually, but as we’ll explore today, they’re actually exceeding others easily, and are also different in tuning from the iconic VxV that I reviewed previously. This means that FiR Audio NE4 will be compared with the best of the best, including Ambient Acoustics MAD24 (3500 USD), CTM Clear Tune Monitors Da Vinci X (2400 USD), Unique Melody MEST MK2 (1500 USD), Lime Ears Aether R (1400 USD), FiR Audio VxV (999 USD), Final Audio A8000 (2400 USD), and Campfire Ara (1300 USD). 



FiR Audio is a growing company from the USA, with a rich product offer. They have everything, from fairly affordable IEMS, all the way to super flagships that use complex driver setups. The company makes both universal IEMS and Custom IEMS, so you can get a version that will always be a good fit for your ears. FiR Audio is one of the best companies to order from, they have outstanding warranty, and still having VxV, I can say that they have some of the best build quality levels out there. 

It should be noted that I have absolutely no affiliation with FiR Audio, I am not receiving any incentive for this review or to sweeten things out. I’d like to thank FiR Audio for providing the sample for this review. Every opinion expressed is mine and I stand by it. The purpose of this review is to help those interested in FiR Audio Frontier NE4 Neon 4 IEMs find their next music companion. 


Product Link

You can grab one from www.amazon.com here: https://amzn.to/3Rybfh7

If you’re in the UK, you can grab one from www.amazon.co.uk here: https://amzn.to/3SqBfw8

And if you’re from Europe, you can grab one from www.amazon.de here: https://amzn.to/3SIczil


Build Quality/Aesthetics/Fit/Comfort

The build quality of Ne4 is insane, as you’d expect from an IEM costing 2299 USD, but they’re also quite different from most IEMs out there. Although most IEMs use the same idea of having a single shell with some ventilation, FiR Audio made that ventilation different, and added kinetic bass drivers on NE4. The universal has a one-year warranty, while the Custom version has 3 years of warranty. 

We have machined aluminum casing, with a sapphire glass faceplate. The tech behind FiR Audio Neon 4 has one Open Driver Balanced Armature for Bass, 1 Open Driver Balanced Armature for mids, and one Open Driver Balanced Armature for highs, this one also having SoundReflector. There is also one 10mm kinetic dynamic bass driver, which is fed into FiR Audio’s Kinetic Bass Port, that large ventilation you see on the inner part of the IEM. 

What I appreciate the most about FiR Audio’s Kinetic Bass technology is that you both feel and hear the sound of that driver. Basically, the driver is ported to the side of the IEM facing your ear, conducting the bass to your ear, but it is also feeding sound to your ear. Thanks to this clever design, you don’t need specific tips with NE4, and any tips should work just fine. I find this perfect because it keeps the sonic signature and tuning more consistent when using NE4 and helps everyone hear the same thing when using them. 

The company also has their Atom Venting mechanism, which is a sound pressure relief system, so you never ever get any kind of driver flex with FiR Audio IEMs. It works as intended, and there are even flavors of it, with the universal versions using the easily replaceable Atom XS modules, that can change the level of bass and passive noise isolation NE4 offers. This whole tech helps you listen for longer periods of time, and at safer levels, with less hearing loss. Also, this helps towards the IEMs not needing specific tips, and they stay very consistent in sound regardless of the insertion depth, or other personal factors, NE4 staying very similar across listeners, despite different biology and anatomy of the ear. 

We also have something named Rigid Technology, which is new and what it basically means is that NE4 uses a series of technologies to improve the reliability of Ne4. First off, the 2-Pin connector is better and tighter than most connectors on the market, and also removable, so it can be serviced if it breaks. There’s also a Rigid Snap Screen, which is the dust filter at the tube bore, and although at first it looks a bit too different from what you see on other IEMs, it is easily replaceable. CIEMs also come with RCX or rigid coaxial, which is rated for 5000 connections, and is a new standard for aftermarket cables. Also, for CIEMs, there’s the Rigid 3D shelling, which makes them more reliable in time, and FiR audio has shells 20% thicker than the industry average, to help you have a better experience for longer with their IEMs. 

We also have the Open Acoustics System, which is basically a name for the tubeless design FiR Audio developed for their IEMs. This is magical, because instead of using tubes that can depreciate sound, they have a Sound Reactor module. This is something unique to FiR Audio, at least at this moment, and having a tubeless design is not new, but having specific components to pretty much gather all of the sound and then pump it is pretty cool. The Sound Reactor is a piece that uses natural acoustics to shape the sound, and it will inherently be more natural than what IEMS with filters and dampers will sound like. There’s also a tiny piece named the Sound Reflector that basically is a way for the treble driver to be employed right in the sonic tube of Ne4, and to have a miniature acoustic chamber that reflects its sound for the least fatiguing and most natural sound. 

I’m happy to say that NE4 made me write a lot, it is good for companies to challenge the existing standards, and FiR Audio is one of the best companies to experiment and develop new IEMS. The comfort of wearing NE4 is excellent, they have an ergonomic design, the subsonic driver has good contact with my ears regardless of the tips I tried, and generally they are a pleasing pair of IEMs to use. 

The default cable isn’t quite as interesting as some aftermarket options such as Plussound Copper+, STE AG W16 or Effect Audio EVO 1, but it does a very fine job for a default cable. Most surprising part is that the default cable actually has a superb sound, and even though it is not quite as ergonomic and good looking as aftermarket options, it sounds super good, and I noticed very little improvements using aftermarket cables.


Sound Quality

Starting with the overall sonic signature, NE4 is truly unique in how raw and impactful its bass is, how sublime the midrange clarity and precision is, and how clean and crisp the treble is. Truly, it is a U-shaped signature, which grows stronger in the sub lows and the upper ranges of its treble, plus works well for contemporary music, regardless of whether we’re talking about metal, rock, EDM, Pop, or even low-fi and indie music. NE4 has one of the widest soundstages out there, and while VxV surprised me by how enjoyable and natural it is, NE4 surprises me by how clean and explosive, but also wide and holographic it can be. One surprising detail I noticed is that aftermarket cables do not improve the listening experience too much, and even if you’re crazy enough to go for cables that are 1000 USD+, the default cable of NE4 will be able to keep up, at least sonically. 

To drive FiR Audio Ne4, I’ve been using a comprehensive selection of DAPs including iBasso DX320, Astell & Kern SE180, Astell & Kern SP2000T, iBasso DX170, Lotoo PAW 6000, Dethonray DTR1+ and FiiO M11 PRO. I’ve also dabbled a bit in portable dongle DACs, as NE4 is rather easy to drive, but the quality of the source plays a role in the final sound of FiR Audio NE4. I noticed that Ne4 can safely be driven from basically all sources, and although it has a somewhat low impedance of 22 OHMs, I noticed some minor hissing with most sources I tested NE4 with. This hissing won’t be audible with music playing, and with Astell & Kern SE180 it was the lowest, and it was quite a bit higher with sources such as Dethonray SG1 Pegasus

The bass of NE4 is as impactful as you can imagine a live concert bass to be. The sub-low end reverberates throughout your head while listening to NE4, with all the width, depth, thickness and impact you hear coming from multiple 20″ large woofers during a concert. Of course, a more colored / warm source like Dethonray SG1 Pegasus can help with this feeling, and a more neutral source like iBasso DX320 can bring it to more natural levels, but it will always be well extended, punchy and NE4 has punches for days to kick you back into shape whenever you’re feeling low and down. The entire bass is rich, they have a full presentation, and never run out of substance. Even on rock songs, you can hear the imposing presence of bass guitars, but not in a bad way, they blend really well with the rest of the mix, and NE4 makes many detail-centered IEMs seem too neutral and bright, as what I’m hearing from NE4 is what I’d consider the ideal quantity of low end a song should have. Bold and raw, deep and powerful, this is how the bottom end starts a great piece. There’s a certain warmth and sweetness to the low end that transfers to the midrange too, but this is different from your typical dark, lush or smooth IEM that has just some extra bass, NE4 has a really controlled bottom end that has a specific sweetness to it. 

FiR Audio was not joking when they said that they can fine tune NE4 to be a masterpiece of detail and resolution, and quite honestly, they have about the same level of detail and resolution as Audeze LCD-5 and HIFIMAN HE1000 V2, or rather somewhere in between. NE4 was tuned to be very rich, natural and to sound organic, but never be fatiguing, and all the tech FiR Audio implemented to keep those IEMs fatigue-free are doing their magic, as the textures are always there, guitars are super juicy and have a really dynamic and colorful presentation, but are never fatiguing, and even songs that have been horrendously recorded can be tasted and enjoyed with a glass of wine, or well, in NE4’s case with a strong coffee, or an energy drink. Energetic, peppy and ready to kick is how I’d describe the midrange of Ne4. Although the bass quantity and the treble quantity is slightly higher than the midrange, you never hear the voices in song to be distant with NE4. In fact, the mids of NE4 are present and they develop into a full-fledged soundstage, with extreme width and depth, giving a very holographic presentation, especially when you remember that you’re using an IEM. The stage can be compared to most open-back headphones, being between HIFIMAN HE1000 V2 and Audeze LCD-XC. The instrument separation has that accurate render that you’d expect from an IEM, but NE4 has the dynamics of a speaker rather than the compressed presentation you fear you’re getting with IEMs when going mini. 

Progressing forward to the treble, FiR Audio was not joking about being able to eliminate all the fatiguing parts of the treble, and NE4 comes with the advantage of having super clean and strong treble, but all that energy can be found in the main treble body, and the upper treble rather than the lower treble or the upper midrange, so NE4 has a rare, truly airy and well extended sound that’s neither metallic nor harsh, but rather natural, clean and airy. There’s so much treble extension that you truly can feel like you’re not wearing IEMs, and NE4 is quite sensitive to source material, easily revealing both mastering and mixing differences, but being able to somehow make everything sound pleasing and enjoyable. It always applies this signature it has over songs, so regardless of whether you’re listening to a really bright or a really dark recording, it always ends up having a good presence on both the bottom and the top end, and the midrange always ends up being fairly detailed and clean. 

Once again, NE4 shows a surprisingly dynamic and punchy presentation that gives an immediate feeling of vividness and color, it is always controlled and keeps you coming back for this energetic, and punchy signature. I would say that as long as you’re not looking for a relaxing and smooth signature, NE4 should be perfect for you. In fact, as we’ll learn later in this review, this signature grew on me so much that right now NE4 is the IEM I use the most personally, as I really love and enjoy its signature. You can say that NE4 is one of the most engaging, full, rich and sweet-sounding IEMS in the whole world. 



FiR Audio Frontier Series NE4 (NEON 4) vs Lime Ears Aether R (2299 USD vs 1400 USD) – We start with a pretty fiery comparison, Aether R being one of my favorite IEMs so far. The comfort is slightly better on NE4 though, because it has a somewhat smaller body and more ergonomic design. The default package is considerably more impressive on Aether R, but the most essential part of the package, the cable, is better on NE4. Passive noise isolation is about the same between them, and both are about as hard to drive, but Aether R is slightly more sensitive to hissing and source noise. We have a more natural, cleaner and more U-Shaped sound on Ne4, which sounds more vivid, more colorful, wider, more holographic, and has better instrument separation. Lime Ears Aether R is thicker, richer, and somewhat more natural, but has a rolled off treble by comparison, and isn’t quite as peppy and impactful as NE4. NE4 has a wider soundstage, with a more holographic presentation. Driving NE4 is somewhat easier than Lime Ears Aether R, and Ne4 is good with a wider selection of sources. 

FiR Audio Frontier Series NE4 (NEON 4) vs Final Audio A8000 (2299 USD vs 2400 USD) – I really wanted to mainly place NE4 against more pricey competitors, because as I already figured it is a high-quality IEM, it will mainly make sense if it outdoes hard to beat enemies, so A8000 is a perfect competitor. Now, Ne4 is a different IEM, with better comfort, and an improved ergonomic, making A8000 seem large by comparison. The default cable is slightly better on A8000, but the tips aren’t quite as nice as the default tips of NE4. We’ve got a different sonic signature, with NE4 sounding much stronger in the lows, having more impact, and being much less fatiguing and more natural, while A8000 is a really bright and revealing sounding IEM. To put it this way, A8000 can really highlight some details that NE4 highlights less, but it comes at the cost of the bass being much less impactful for A8000, while NE4 is the ideal U-shaped signature IEM. The passive noise isolation is better on NE4, it is a bit easier to drive and it is less sensitive to hissing from the source. NE4 also has a slightly better soundstage, with a wider and more holographic presentation, although instrument separation is about the same between them. 

FiR Audio Frontier Series NE4 (NEON 4) vs FiR Audio VxV (2299 USD vs 999 USD) – Both of those IEMS being designed by Fir Audio, it is interesting to notice that both have excellent ergonomics and should be comfortable for all ears shapes and sizes. The package is better on NE4. The sonic presentation is extremely different, with NE4 being much stronger in the bass and treble, more V-Shaped, more aggressive, and more revealing, with much more detail, at the expense of making VxV sound much more relaxing and natural, smoother and more musical. Indeed, NE4 isn’t a particularly relaxing IEM, but it has beautiful musicality for guitars and individual instruments, the whole mix sounding usually vivid and engaging. The source sensitivity is about the same between NE4 and VxV, both have good soundstage, but both instrument separation and soundstage width is considerably higher on NE4. Passive noise isolation is slightly better on NE4 as well. VxV sounds like a smooth, musical, rich and natural IEM, while NE4 sounds V-Shaped, energetic, impactful, colorful and vivid. 

FiR Audio Frontier Series NE4 (NEON 4) vs Campfire Ara (2299 USD vs 1300 USD) – Starting with the comfort, Ara is slightly more comfortable than Ne4, as it has a smaller body, better ergonomics, and is easier to fit with smaller ears. Build quality is excellent on both, but the default cable of NE4 is better than the default cable of Ara. The sound and sonic signature is considerably bossier, with more impact and a better bottom end on NE4, which has much more bass, making Ara sound quite bright and thin, especially in direct comparison. Both IEMs have outstanding speed and resolution, NE4 provides more finer detail, while Ara is airier and has a lighter overall sound. Ara is more relaxed, while NE4 is more aggressive and forward. For rock, metal, pop, EDM, and electronic / commercial music in general, NE4 is more colorful and vivid, while Ara is still in my top 10 favorite IEMs, having a better price / performance ratio as it is 60% the price of NE4. Soundstage is wider on NE4, instrument separation is also a bit better on NE4. Those are fine differences, and you’d need them side by side to really appreciate the differences, as otherwise they can be quite similar, especially if you’re trying to compare from memory. The passive noise isolation is slightly better on NE4, and the source sensitivity is much higher on Ara which can get hissing much more than NE4. Ara sounds neutral, clean and precise, while NE4 sounds U-Shaped, engaging, vivid and colorful. 

FiR Audio Frontier Series NE4 (NEON 4) vs Unique Melody MEST MK2 (2299 USD vs 1500 USD) – We have a similar level of comfort here but being able to wear tips with lower level of stickiness makes me prefer NE4 for daily usage, as they simply come through as more comfortable. The build quality is also slightly better on Ne4, as they have metallic shells and a smaller body that fits better on all ears. The cable included is better on Unique Melody MEST MK2, has a soldier build, and it is more ergonomic. Sonically, they are not quite the same, with NE4 having a considerably more natural midrange and upper bass / lower treble, but also better resolution, and a richer sound. I prefer the overall clarity of NE4, and the treble impact, but also the bass, which goes lower, with better impact. The soundstage has about the same width and instrument separation is about equal between them, which puts both Mest MK2 and NE4 at super levels. MEST MK2 is slightly more sensitive to source hissing, and is also slightly harder to drive than NE4, requiring better sources to sound good. Passive noise isolation is about equal between MEST MK2 and NE4. Unique Melody MEST MK2 sounds colored in the midrange, with a stronger lower midrange and upper bass, and less treble extension, while Ne4 is also U Shaped but with a more airy and more balanced midrange presentation. 

FiR Audio Frontier Series NE4 (NEON 4) vs CTM Clear Tune Monitors Da Vinci X (2299 USD vs 2400 USD) – We need more detailed battles, and this comparison begs to ask a serious question, on which is more detailed. First off, the comfort is better on NE4, which has a smaller body, and a more ergonomic build, also they are easier to wear, working better with literally any set of tips, while you need to fiddle a bit with Da Vinci X to get a good comfort. The cable of NE4 is much better than the cable of Da Vinci X. The overall build quality is comparable and excellent on both, but the signature is actually quite different, with NE4 having a much stronger sub bass and bass quantity, much stronger impact, and a higher number of lows, while Da Vinci X sounds sensibly brighter and more fatiguing. The maximum detail level is actually about equal, with Da Vinci X resolving more detail in the midrange and treble, but NE4 resolving bass nuance and finer details much better. The better impact and bass on NE4 lead to a much better presentation for rock, metal, EDM, Pop, and unless you’re an avid detail addict, I would consider going with NE4 instead of Da Vinci X, the price also being in the advantage of Fir Audio’s creation. The soundstage is wider on NE4, instrument separation being about the same. Both are really easy to drive and about as sensitive to source hissing / impedance. Passive noise isolation is about equal between them. 

FiR Audio Frontier Series NE4 (NEON 4) vs Ambient Acoustics MAD24 (2299 USD vs 3500 USD) – We have two titans here, both with good tech and strong companies behind, so it is interesting to first notice that the comfort of NE4 is higher than the comfort of MAD24. NE4 is smaller, more ergonomic in shape, and has better overall construction quality, having metal and sapphire in the build, compared to mostly resin and plastic in MAD24. The accessory setup is slightly better in NE4 too, as they have a more modern transport case, and a better default cable. The sonic performance is quite different, and although NE4 has a considerably lower number of drivers, it also has a better overall resolution, a richer, more coherent sound, with better fluidity for the midrange, and a stronger overall impact. The sub bass has better extension, and the dynamics are also better on NE4, the signature being more energetic, with a higher quantity of bass and treble, and a recessed midrange. I generally prefer the sound of NE4 for rock, metal and most music, although if you’re easily fatigued, MAD24 is smoother, and has a thicker, more meaty sound with a stronger presence for voices, and a lower treble extension and lower treble presence. Both IEMs are pretty detailed, but the ultimate crisp detail can be found in NE4, while MAD24 is more of a rich and musical, smooth and relaxed presentation, where NE4 can be considerably more aggressive, more engaging and more uplifting as well. The soundstage is wider on NE4, while the instrument separation is also better on NE4. NE4 is slightly harder to drive than MAD24, responds more to source quality, and has lower sensitivity to hissing compared to MAD24, which is really sensitive to source quality. Passive noise isolation is about equal between them. 


Value and Conclusion

I’ve spent so much time with FiR Audio NE4 that they basically became my new favorite IEMs. They cost quite a bit, but they’re an IEM you won’t forget, they are to me now what my favorite IEMS have been to me in the past, they are perfect. The price point is high, but the performance is higher, and they have no inherent flaws or disadvantages, so for a technologically advanced product, I feel happy to report that they’re fully worth their asking price, and you won’t feel like you’re paying too much for a product not worth its asking price. 

Even better, the overall quality, even compared to what else is available on the market regardless of the price range, is so good, that FiR Audio NE 4 will be part of Audiophile-Heaven’s Hall Of Fame, as one of my favorite IEMs ever created. 

At the end of the day, if detail, but also impact is your thing, if you enjoy outstanding instrument separation and if you want the best IEM experience you can get for a V/U shaped signature, and if you can afford it, I fully recommend FiR Audio NE4, or Neon 4 from their frontier series, as one of the best IEMs I have tested to date, and my personal favorite sonically up to this date. 


Product Link

You can grab one from www.amazon.com here: https://amzn.to/3Rybfh7

If you’re in the UK, you can grab one from www.amazon.co.uk here: https://amzn.to/3SqBfw8

And if you’re from Europe, you can grab one from www.amazon.de here: https://amzn.to/3SIczil




  • Fir Audio Frontier Series Neon 4 (NE4) IEMs
  • Audio cable 
  • Leather transport case 
  • Warranty
  • Instructions

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Full Playlist used for this review

We listened to more songs than those named in this playlist, but those are excellent for identifying a sonic signature.  I recommend trying most of the songs from this playlist, especially if you’re searching for new music! The playlists are different for Spotify, Tidal and Youtube, and based on the songs I enjoy and are available on each!




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  1. Gerald

    This is an amazing review, thank you so much for all your effort and hard work, George! Loving your work!

  2. […] good and I never felt like I’m draining Hiby R6 III too fast, and in fact, at least with FiR Audio NE4, I was still above 85% after two hours of music listening, browsing, in Class A, over the 4.4mm […]

  3. Charles

    Thanks for review. I found it more accurate than others. I now have the neon4 and it is end game for me. I was able to hear the kr5 before purchasing , but the Ne4 is the one that sounds more like the xe6. I now using optional red module with ne4, which opens up Soundstage more and evens out the bass. It trounces both Mest2 & Indigo for me.

    1. George Dobrescu

      I’m really happy to hear you’re having such fun, and I hope you’ll also get a dream source to pair with it and to complete your experience!

  4. Q Mann

    Thank you for improving audiophile-heaven all the time, I’ve been an olde reader and I noticed how you keep improving everything for us, thank you, George!

  5. Mick

    Amazing review! You’re so eloquent with your words, and actually do touch on things that matter, that you’re the only reviewer I really read nowadays.

    In fact, you even managed to convince me, George! I ordered a pair of Ne4 just now, hoping they’ll sound as good as you describe them!

  6. Joshua Moreno
    Joshua Moreno

    Thank you for the detailed review of the Fir Audio Frontier Series NE4 IEMs. It sounds like they are a great option for audiophiles and musicians alike. I appreciate the honest opinions expressed in the review. Thanks again for sharing!

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