FIR Audio M4: the sound hyperrealism

Hi friends!

I am glad to inform you that today we continue our acquaintance with the line of in-ear monitors from the American brand FIR Audio! Today our guest is the second oldest model, if you count from top to bottom from “M5”, which has already caused noise in the audiophile environment - FIR M4.

Like all IEM / CIEMs of the FIR brand, the M4 has a hybrid design: here, as you might guess from the model name, there are four drivers (1DD + 3BA). In addition, there is an integrated Atom-X module inside and a unique "Tubeless Design" enclosure design. This is a patented FIR Audio technology in which they have managed to eliminate acoustic tubes as well as separate driver chambers. In such solutions, the most accurate calculation is necessary for the correct location of all audio components inside the IEM / CIEM, otherwise re-reflections and resonances cannot be avoided. But the FIR company with honor bypassed all the "pitfalls" and gave an excellent result, and for that it has a special respect.

I understand that with the current, not quite healthy pursuit, organized by a number of brands and their marketers, for the number of drivers in IEMs and the desire to "stick more inside a small box", in a small IEM case, the number four may seem modest, but I assure you , do not jump to conclusions. After all, the recipe for good sound is not in the number of drivers, but in quality, skill, technical literacy, implementation and, which is very important, taste and understanding, the feeling of sound by the manufacturer himself. And the FIR M4 proves it convincingly!

Well, if after this review you will be interested in other FIR Audio developments, then on our website you can also get acquainted with their M5 and VxV models.


Text by Alexey Kashirskey aka Hans Barbarossa


3D-printed metal shells

4-driver tubeless system (1 x dynamic driver, 3 x balanced armature drivers)

Range: 10Hz to 20kHz

Impedance: 6.4ohms

Сable 1,2m, with MMCX connectors

Unlimited Sound: CIEM or IEM?

Before starting the review itself, it is worthwhile to dwell on the fact that in-ear monitors of the FIR Audio brand can be ordered in both universal (IEM) and custom (CIEM) versions - the choice is up to the buyer. The exception is the VxV model, which is produced exclusively in the IEM body.

Well, for those who have not yet encountered CIEM, I can assure you that the procedure for ordering individual CIEM is not at all difficult. You need to go to the website, register, go to the "Designer" menu, select the desired model, its design (appearance, connectors, cable length) and pay for the purchase. Then you go to the hearing center, make impressions of the ears there and send them to the manufacturer. After that, look forward to the arrival of your exclusive CIEMs.


In our case, the M4 model is made in a universal design. And now it's time for us to go directly to the acquaintance with this four-driver miracle!

Appearance kit and ergonomics

M4 comes in a small black cardboard box. On its front side, in gold embossing, the FIR Audio company logo is depicted in the form of protruding bunny ears, from which sparkling sun rays scatter in all directions. Nice, perky and tasteful, well done!



In the box we find IEM encrusted in a foam base with a removable cable (MMCX / 3.5 mm) already installed, a stylish black leather case-washer with an embossed brand logo, intended for storing and carrying in-ear monitors, instructions, a warranty card and interesting colorful stickers ...

Inside the case neatly fit 4 pairs of silicone and one pair of foam tips, as well as a brush for cleaning sound pipes.




In general, the kit is from the category "everything is here and a little more."

The elegant black M4 IEM shells, including the aesthetic champagne faceplates, are made of aluminum. On the left faceplate, we again see perky protruding bunny ears, on the right - the name of the model "M4".

Everything looks very nice and stylish - this approach in design is very close to me personally.

The elegant teardrop-shaped headphone housing is lightweight, durable and extremely comfortable. It is smooth and tactile to the touch. The straight sound pipe is covered with a metal mesh that protects the IEM from moisture and sulfur. On the upper side of the shell there is a connector for a removable cable. Next to the connector are two tiny holes: an integrated Atom "Air Transfering Open Module" and a compensation hole for setting up a dynamic driver. It is pertinent to recall here that the M4 uses "Tubeless Design" technology: there are no acoustic tubes and separate chambers for drivers.

The ergonomics of the headphones are great. Wearing expected behind the ear.



Coffee-colored braided cable made of silver-plated copper litz wire. It is glossy, elastic, MMCX connectors, with a 3.5mm TRS jack and a splitter in the same style. The cable length is 1.2 meters. If you wish, you can replace the cable with any other with MMCX connectors, although personally I find it very pleasant.


As I mentioned earlier, the M4 has a hybrid design and is built around four emitters: three (BA) and one (DD) with an integrated Atom module. Here it is necessary to clarify what the Atom-X is - it is a metal cylinder-valve that acts as an acoustic filter for fine-tuning the sound of headphones. It also releases the air lock that forms between the earpiece and the eardrum. This way, the pressure on the eardrum is reduced and our hearing is not exposed to any risks. In the universal IEM shell, the valve is built into the headphone structure. We have the same case.

Perhaps the only thing I would find fault with is the MMCX connector. In my experience, such a decision often caused disconnections, although, of course, I understand that the company wanted to please many audiophiles who like to play with their collection of cables. But then why wasn't the more reliable 2-pin connector chosen? Moreover, FIR Audio has its own wonderful RCX connector / connector that they install in their CIEMs, and personally I really like it. I think that soon the universal version of their in-ear monitors will move completely to the new RCX. However, these are just my quibbles and it is worth seeing how the MMCX connection behaves this time.


Well, the kit, appearance, workmanship and ergonomics of these IEMs evoke extremely positive emotions in me, but, of course, we gathered together mainly to experience the main magic of the FIR M4 - let's move on to the sound!

Sound impressions

The listening was carried out on the equipment: MyST DAC 1866OCU V.2, Lotoo paw Gold, iBasso DX220 (AMP7), iBasso 220 MAX, QLS QA-361, iFI micro iDSD BL and iFi ZEN DAC + ZEN CAN.

Initially, FIR M4s were burn-in for 40-50 hours.

With all sound sources the M4 sounded good, their "voice" varied slightly depending on the sound source and the tips used.



I highly recommend choosing tips responsibly, as they make a significant contribution to the sound image of the M4.

There is another important feature of the M4. The sound of these IEMs is decisively dependent on the power of the sound source. The better the audio path and the more solid the amplifier, the more M4 is able to show itself in all its glory.


The sound of the FIR M4 is clear, well-balanced, open and unusually melodic. This is a light U-shaped frequency response, with a neatly accentuated subbass area, and light, elegant emphasis in the high-frequency register. These IEMs demonstrate excellent dynamic range and stunningly convey volume, and in it the localization of apparent sound sources in space: higher-lower, further-closer - clearly and scrupulously building a virtual "sound stage".

This is realized so skillfully and at the same time artistically that you no longer just listen to music, but begin to see every sound in the enchanting three-dimensional image that appears in your head. The immersive effect is such that at times it seems that you can touch this or that musical instrument and even the sound itself flowing from the instrument.

I called this sound magic the M4s do "sound visualization!" When musical images are built, as if in a picture of hyperrealists, with crazy detail, amazing volume, extreme harmony, layering, giving out excellent melody at the output. This is somewhat reminiscent of the sound of a studio monitor with an AMT tweeter. Precise, clean and neutral, with a slight elegant coloration in the lowest and highest registers. Moreover, the Highs here in some places are served by a "spectacular spark", which, like a sparkler, flares up, illuminating the space around itself, and scattering into small specks-stars, sharply fades away, falling into the darkness. Incredible beauty!



Low frequencies are transmitted tightly, accurately and quickly, with good texture and excellent articulation. There is a crisp clap, a tight, biting beat, and a textured nimble bass. It should be borne in mind that the lower case is not very forced, it takes more quality than quantity. The rolls of the drum set blows, like artillery shots, scatter on both sides of the listener, accurately conveying the force of the blow. The density and speed with which the M4 is working out lowercase is simply amazing.

The bass is fast, punchy and extremely naturalistic. It is presented in a lively and temperamental manner in a neutral manner. There is not even a hint of rumble and booming, but there is precision in the reproduction of timbres combined with excellent balance.

The mids are clear, like a mountain stream, neutral and smooth, with excellent texture and excellent resolution. The M4s showcase excellent detail and astounding visualization of sound images in a space with detailed, holographic sound delivery, where no detail escapes the listener.

This is a well-balanced and at the same time emotional performance, where all the elements of the composition are presented with extraordinary precision, large and versatile, with amazing smoothness and informational content. Strings and wind instruments sound clean and distinct, and the vocal parts are transmitted smoothly, naturalistic, very beautifully and moderately expressive. This is a fairly harmonious, spacious and very musical manner of performance.

And here it is simply necessary to return to one of the most important advantages of the M4 - the transfer of the volume of virtual space. Sounds, as if by the wave of a magic wand, as in a three-dimensional image, are scaled and lined up, both in the head and beyond, into a multifaceted harmonious canvas, on which, with the help of sound and imagination, we can build our idea of the spatial form of a sound wave. so to speak, to revive what was heard. And this is just an amazing quality - aerobatics!

High frequencies sound quite clear and intelligible, refined, with good articulation and enviable correctness. This manner of HF processing is a bit like the transfer of this register by an isodynamic or AMT driver. There is a slight accent in the form of a light crumbly spark with a slight brightness.

On the one hand, in this case there are no exquisite after-sounds, on the other hand, it is this manner that gives the overall sound of originality, expression and charm. It is worth noting the fact that with a generally rather comfortable manner, in some poorly mixed and overly bright compositions, such a feature can lead to minor problems and unobtrusive sibilants. Although, in all honesty, I want to say that it still sounds effective, beautiful and comfortable.

In fact, I noticed that this property of the M4 directly depends on the quality of the sound source. If we take a better path and a more powerful amplifier, everything is flawless with the Highs, only the advantages of this frequency range are audible: its peculiar, euphoric manner, which definitely catches me.

By the way, the selection of the sound source also has the most direct impact on the transfer of volume, width and depth of the virtual "sound stage".



In terms of genre preferences, in my opinion, FIR M4s are quite tactful: they play interestingly as classical music, instrumental, jazz, electronics and rock. In principle, things are also pretty good with brutal genres, but it depends more on the quality of the mastering of the compositions. Well, these IEMs play classical music and jazz just great!


M4 - amazing in-ear monitors! FIR Audio mixed in one cauldron exceptional technical competence, impeccable taste and brilliant ideas, and on top they also clearly seasoned it all with a miracle potion. As a result, we have before us “TOTAL IEM” - a model that, in my opinion, deserves the closest attention of all who dream of an exceptional sound.

Such an exquisite audio signature, in my opinion, is able to satisfy the needs of the most demanding music lovers and audiophiles.

You can order the FIR M4, like any model in both (CIEM) and universal (IEM) versions, on the official website for $ 1899.

Yes, the price is not small, but that is how much the sound costs, from which it takes your breath away, and the imagination is turned on to the fullest.

As you probably already understood, I recommend these headphones for purchase without the slightest hesitation.


Sound, ergonomics, design, workmanship, kit.


MMCX connectors are not the best solution in my opinion.

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