FIR M5 Review: First Class

FIR Audio M5 Review: First Class

Everyone, it is time for us to take a trip down the rabbit hole. FIR Audio is a new IEM brand founded in 2018. Though while the FIR brand may be new to the competition, the founder himself is not a newbie in the industry at all. Bogdan is one of the four Belonozhko brothers who are all acoustic engineers and musicians. He is also the ex-CEO of 64 Audio (formerly known as 1964 Ears), one of the leading UIEM/CIEM companies. FIR Audio is another chapter of his work that pursues the same high-quality standards as 64 Audio did, yet with differentiation. Today’s review will be dealing with the M5, FIR’s latest flagship IEM.




FIR M5 is available in both universals or custom-molded IEMs. All FIR products come in the same box with the FIR logo sitting in the upper front. The golden stripes and dots that spread from the logo are filling the front side of the box, giving the packaging a simplistic yet stylish look. The model number is labeled with a black-gold sticker at the bottom front of the lid, which in this case it is labeled as M5. Once the lid is removed the IEM reveals itself along with its accessories. Other than the earpieces, M5 follows with a quality 3.5mm stock cable, a leather case, a cleaning tool, sets of foam tips and silicone tips, a warranty card, a user guide, and some FIR stickers. The leather case feels very nice in the hands and well-built. The overall offerings from the packaging may not appear so exceptional, yet the quality cable and the premium case do their job to make the deal pleasing enough. 




M5 is available in either UIEM and CIEM. In the case of CIEM, FIR provides various design customization free of charge. FIR’s universal shell is identical throughout the line-up, using a whole CNC-machined, anodized aluminum. The sandblasted surface is fine and smooth with a matte black coating that gives a simplistic yet sexy look. The faceplates are done in a deep, vibrant red color that goes along with its body. Interestingly enough, FIR uses MMCX connectors for their connection standard – an extruded form to be exact. This reminds me of oBravo’s MMCX-OB connectors. Though the difference is that the extruded portion of the connector will be covered by the plastic cover from the cable’s side. Alongside, FIR Audio’s extruded MMCX connectors are fully compatible with ordinary MMCX cables. 



FIR Techs: Direct Bore, Tactile Bass, and ATOM

M5 consists of a tribrid driver setup, sporting a 10mm dynamic driver for the lows, 1BA for mids, 1BA for mid-highs, direct 1BA for highs, and direct EST (electrostatic) driver for the ultra-highs. One of the key structure from M5 is FIR’s Direct Bore Structure, where EST & BA tweeters are installed right in front of the nozzle, enabling the sound to be pointing straight into the ear canal. Alongside, both BA and EST tweeters are vented (spoutless) that allow the drivers to carry maximum details as well as creating a natural expansion. The Direct Bore Structure also decreases muffling and distortion, aiding the sonic accuracy even further.


The dynamic driver is tuned just as finely as the other drivers were. This 10mm bass driver is taken with an opposite approach – called Tactile Bass Technology. Unlike the upper frequencies’ Direct Bore Structure, Tactile Bass Technology is an acoustic structuring where the dynamic driver uses the entire inner chassis as a transducer, producing a richer and fuller bass response. This also causes natural resonance within the chassis to let the listener physically feel them, hence the word “Tactile”.


Last but not least, M5 features what is called ATOM Vent System, a pressure-releasing system that is unique to FIR IEMs. ATOM stands for ‘Air Transferring Open Module’ which is a simplified version of 64 Audio’s APEX system. FIR introduces that the team has tested a number of nano-thin membranes and foam materials to create ATOM, resulting in super compact filter size, lower vulnerability to air volume, improved sound presentation & soundstage, and most importantly, relieved ear fatigue.




The stock cable is made of 8-braided Silver-plated Copper OFC wires. Mildly interesting that the outer sleeves are brown despite it being a silver-plated cable. M5 uses MMCX termination for the cable connection, yet male sockets are fully compatible with ordinary MMCX. However, the female connectors from the cable are incompatible with most other MMCX IEMs due to the extruded plastic housing covering the female connectors. Well, I would not stress much about that since the earpieces themselves have no problem connecting to other MMCX cables. Though unless you are planning to match an alternate/upgrade cable, I recommend sticking with the stock cable as the extra layer of plastic cover providing better durability. Besides, M5’s stock cable does a flawless job bringing out the intended performance, so feel free sticking with it unless you really want a cable upgrade. 



Sound impressions: Lows

It is easy to make little attention to the dynamic driver from an EST tribrid IEM since the fancy tweeters, right? Well, that would be a bad, bad idea because M5 produces one of the finest and realistic bass response I have experience from an in-ear.  Though M5’s bass quantity scales close to slightly v-shaped IEMs, so it is not a basshead IEM. “So what is the big deal?” you might ask. It is about the quality, not the quantity. The name “Tactile Bass” makes itself evident as the reaction speed of the bass is lightening-fast with reverbs that deliver life-like vibrations. Through the natural sound formation that happens inside AND through the chassis, lows display a mellow atmosphere with deep and thick pigments to their colors. This leads the bass to become large, inundant, and heavy, but at the same time showing extreme speed, cleanliness, and accuracy.  


The tone is neutral with a mildly warm temperature. The ultra-low details show an evident presence with great clarity and tightness. Also, ultra lows would not get overpowered by the upper lows whatsoever. The sound flow along with the bass quantity is outstandingly leveled, showing a steady, reference-style characteristic. Upper lows make strikes that are adamant and neutral. The bass always stays organic, hence they are in no way stiff or metallic in their texture. The solid, thick core of the bass is gently overlaid with soothing reverbs – the end result being dense and tight lows that are fatigue-free and friendly to the ears. 



Sound impressions: Mids

While mids are closer to the ears than the lows, it also shows an impression where mids are on top of the lows rather than it simply being bulged out beyond the lows. Mids are full-bodied with a mild warmth going on. Even though vocals show a thick density, they always seem to be having much airiness and breeziness throughout the mid-range. It scales large and openly, showing an even stronger breeziness compared to the lows. It is sizably impressive that M5’s mids show such openness while having the vocals to sound so moist, thick, and warm. Furthermore, mids are also where M5’s “special-made” creaminess really kicks in. It is a type of creaminess that feels so relaxing and soothing but also pouring out such refined resolution and texture details.


Okay, there might be a fair amount of IEMs that have already been providing such vocals, though M5 is still unique compared to all those. This deep, super-thick creaminess is carried out in a strongly transparent, open-field atmosphere. Plus, it even exudes a glimpse of coolness beyond the lower mids. This is very unusual (surely in a good way) as such “seriousness” is usually carried out based on a closed-field atmosphere with strong warmth going on. It is also common for such IEMs to have that particular stuffy atmosphere in the background of the sound. M5, meanwhile, sounds amazingly relieving, transparent, and clean. Transparent as a glass of water, clean as a brand-new phone screen with its protect film just peeled off. The sound flow in the mids is just as perfectly stable as the lows, not causing a sibilance or turbulence. M5 works out perfectly with both male and female artists as well as showing great stability throughout different genres.



Sound impressions: Highs, etc.

Highs are inspiringly rich. While there are flagship IEMs that show richness driven by skillful finesse, there are also those that show richness driven solely by resolution. M5, in that sense, fits in the latter case. The treble’s Direct Bore Structure along with its vented drivers sure serve a resolution that is on an entirely different level. M5’s trebles show extreme purity and resolution. There is basically zero coloration that gives the treble to ooze a pure air-like atmosphere. The tiniest rustles and details that were unheard from my other IEMs start to drag my attention as I listen to the same tracks with M5. Trebles are expressed “just as it should be” approaches very close to the ears. However, this is where it gets more interesting – even while trebles approach closely to the ears, they also create a life-like staging as they spatially fill the headroom. This special presentation makes the trebles sound immaculate while consisting of a frighteningly good balance. A good balance in terms of both timbre and the overall quantitative balance among all ranges.              


One interesting characteristic I would like to mention has to do with its staging. While the soundstage shows predominant downwards depth, the focal point of M5’s mids and highs are placed a bit higher from the center. As said, lows are well preserved and stretch all the way down to the rock bottom. The Tactile Bass tech does a nice job doing that. Anyhow, such upper-end staging makes the treble sound buoyant, transparent, and even airier. Perhaps FIR M5 is so far the best when it comes to generating a highly natural, opened-air headroom from an in-ear. The separation is spectacular, needlessly to say.  



Comparisons – Faudio Project Y

Faudio Project Y is another great IEM that desires a very similar tuning direction as the FIR M5 does. The similarity between these two IEMs is not only limited to the overall sound signature but also the tone, texture, and even the style of the headroom formation. However, the Tactile Bass equipped on FIR M5 shows its superiority in the low-ends. Although not by a drastic difference, FIR M5 shows a deeper, meatier, and fuller bass reproduction along a bit more sub-bass. Though I would like to note that the low-ends on Project Y is purposely tuned to be flat and rather linear. In the case of Project Y, lows show nice extension and ultra-low presence. However, it is the quantity that is highly controlled to keep the low-end atmosphere as clean/neat as possible. So if your taste of bass lies very close to the reference target, Project Y is no worse selection at all, if not even better.


The Upper-mid transition on Project Y is just slightly smoother than FIR M5. Project Y snakes through the sibilance area seamlessly and smoothly, while FIR M5 leaves a mild crisp as the vocals transition towards the trebles. This does not escalate into a sibilance whatsoever, hence it is difficult to necessarily call either one to be better than the other. In fact, this upper-end crisp adds an adequate edge to the sound, serving the music to feel higher in analyticity. Also, while both IEMs work out nicely with female and male vocals, FIR M5 tends to do slightly better with male vocals and Project Y for the female vocals. FIR M5 provides better pushing force for the mids, breathing in liveliness to the vocals. Project Y, on the other hand, handles the vocals more slowly and carefully, giving some extra feminine touch to the voicing. Keep in mind that all these “vocal matters” are rather insignificant in their differences and should not affect your decision too so much. Still worth mentioning, however. In conclusion, this comparison ends up in a complete draw. They are identical in their tiers along with their sound signature being extremely similar. However, all the small bit of differences are what that impacts the final decision of the end-user.



Comparisons – 64 Audio Tia Fourté

If we are going to review FIR M5, we of course have to bring up the mother brand – 64 Audio. I actually liked it when they used to be called 1964 Ears, but anyway. Tia Fourté is 64 Audio’s pre-flagship IEM that served as a matrix or the basis of the FIR M5. Both IEM fully utilizes the internal chassis as a soundbox along with a fully vented BA driver. So now, time to dive into the topic. The overall sound signature of FIR M5 is fairly similar to Tia Fourté – but with clearer differences compared to how things were with Project Y. Putting it simply, Tia Fourté has a more raw feeling as well as emphasizing more of its “internal headroom”. Highs are more passionately and forcefully pushed up, whereas FIR M5 is just as airy but focuses more on presenting them calmingly. Mids on FIR M5 are bolder and thicker. The surface of the texture also feels to be lightly oiled, giving an extra smooth impression. Meanwhile, Tia Fourté stays very neutral in thickness and with an “unedited” texture expression, blatantly revealing what the music has to got to show. FIR M5 carries a bit more bass quantity, though the difference is not night and day. The ultra-low extension is pretty much in the same tier.


Headroom-wise, FIR M5 feels fuller, bolder, and more up-close in its staging. Sounds like FIR M5 completely won in this field, right? Not really, however. Tia Fourté has its very unique staging formation that is already enough to convince someone to grab them. While FIR M5 goes full force in presenting maximum resolution and clarity, Tia Fourté utilizes its internal chamber to present the sound in the most realistic way possible, hence the opened-up headroom. The charming point is that Tia Fourté never gets to the ambiguous in defining where the staging “ends”, yet it also does not feel to be secluding the end-point of the upper-ends either. This is why FIR M5 might appear superior in terms of staging but not definitely since it is a matter of staging style. In conclusion, by using a metaphor, if FIR M5 is having the music to be “realistically played right in front of the listener”, then Tia Fourté is to have the music to be “realistically stretching out from the listener’s head”.




There are IEMs that deliver eye-popping impressions from the very first meeting that diminish faster in satisfaction due to the intense characteristics. There are also those that leave more discrete and subtle impressions which eventually provide longer, enduring satisfaction. M5 is a perfect example that applies to the latter case. To sum up, M5 shows adequate emphasis for all three bands with extra treble finesse and vast imaging. Also, its charms and unique highlights are brought on in a neutral, fresh manner that does not stale so easily. All FIR technologies work out as a perfect assembly within its ergonomic shell, where the end result is a first-class performance brought within great comfort. I am confident enough to call M5 as a complete representation of what FIR is capable of delivering through an in-ear monitor. For those who are looking to experience the pitch that FIR could provide, or especially looking for a tube-less flagship CIEM which is super rare of its kind, M5 will be the choice that would not disappoint you.




Thanks to FIR Audio for providing the review opportunity in exchange for an honest impression/feedback.

I am not affiliated with FIR Audio and none of my words were modded or asked to be changed.

FIR Audio M5
Ultra natural, reference sound signature
One of the highest clarity/resolution
Clean, neat yet bold bass response
Well-built and comfortable metal chassis
Tubeless design also available in CIEM
Not meant for bassheads
Would've been better to add more options for plug termination by default