Bellos Audio X4: Viva Quartet!

Winter greetings to all lovers of top-notch sound!


Writing about new projects is always exciting. Although, to be honest, it is difficult to apply the word "beginner" to the Bellos Audio brand, because it was created by brothers Vlad and Bogdan Belonozhko (Bellos Brothers), who have 20 years of successful experience in creating various audio products.


And when I finally received the flagship CIEM-monitors X4 from Bellos Audio, I was on the one hand extremely intrigued, knowing the sensitive approach of the brothers Belonozhko to the production and customization of their products, and on the other - a little skeptical, realizing that these in-ear monitors are focused to a greater extent on professionals in the music industry. But all my doubts were dispelled immediately after the first acquaintance with Bellos X4.


Indeed, the company mainly specializes in the production of professional in-ear monitors. Moreover, in the search for new solutions, Bellos Audio engineers resolutely discarded traditional principles and assembled CIEM almost from scratch.


Their latest In-Air Canal technology is an unusually comfortable silicone-covered tip sound tube structure. The CIEM "X" series also incorporates developments we are already familiar with from FIR Audio products: ATOM Venting, Rigid RCX connectors, convenient 3D-printed enclosures, Removable Faceplates for quick replacement of internal components.


Bellos X4 have a hybrid design. Each CIEM houses four drivers of two types: one dynamic driver (DD), three open-back armature drivers (BA) and a built-in 4-way crossover. How does it all sound? Let's find out directly in the review.





Text: Alexey Kashirskey







3 Balanced Armature drivers

1 Dynamic Driver

Frequency Response: 20Hz – 20kHz

Impedance: 16Ω at 1kHz

Sensitivity: 116 dB/mW

Crossover: Integrated 4-Way Crossover

Isolation: -17dB (internal ATOM)




Ordering customized (CIEM) earphones


To order your CIEMs, you go to, register, go to the "Custom In-Ear Monitors" menu, select the model you want and place your order. Then you go to the hearing center, take ear impressions and send them to the manufacturer. You can then eagerly await the arrival of your exclusive in-ear monitors.



Appearance, kit and ergonomics



The Earphones come in a modest cardboard box of white color with an immodest inscription made in USA. Also on the front side there is a brand logo in the form of a butterfly and a photo of the CIEM.




Inside we find a black metal case with the Bellos Audio logo and the name of the lucky owner of the earphones on the lid. We open the case and take out the X4 CIEM with a replacement cable (RCX/3.5mm TRS jack), a pair of spare silicone tips (one of them is already on the CIEM) and a brush for cleaning the sound conduits.





Everything you need and nothing extra, with a professional touch.


The earphones acrylic shell is 3D printed and hand sanded. It has a tactilely pleasant matte black rough surface. The build quality and appearance are beyond praise - we are looking at a custom shell made from an individual ear mold.





And now is a good time to discuss the company's know-how - In-Air Canal technology: a versatile, open, short sound pipe with silicon tip. If you've ever used custom in-canal monitors (CIEMs) before, you know that when you open your jaw, your ear canals change shape, at which point the CIEMs lose their seal, causing discomfort in your ear.




Bellos Audio have found a solution to this very unpleasant problem. The In-Air Canal is a patented design that provides complete sealing of the aperture (entrance) of the ear canal without having to reach beyond the second bend of the ear canal. Using specialized 3D printing software, an impression of each CIEM Shell is designed to fit perfectly and provide unparalleled comfort, thanks to the new elastic oval silicone tip. The ear canals then remain filled with air only, and any change in their shape does not affect tightness or comfort. I can confidently say that In-Air Canal technology works, and Bellos X4 are one of the most comfortable in-canal monitors ever.




But back to the X4. The shell itself is small in size, extremely light and very comfortable, where every curve, every twist and every bulge perfectly follows the shape of the ear. The front panel (faceplate) is removable and attached to the base with three tiny screws. This solution allows for quick replacement of internal components. The faceplate itself bears the brand's silver logo. This elegant minimalism looks insanely stylish.




At the bottom of the earphone is a tiny hole, the very same built-in ATOM Venting module for relieving air congestion (the pressure of air in the closed ear canal exerted on the eardrum). The ATOM Venting also acts as an acoustic filter to fine-tune the CIEM sound and expand the soundstage.


On the inner side of the shell there is a short sound pipe, through the opening of which we can see the open BA driver. The sound pipe is fitted with a specially designed, extremely elastic silicone tip, which, besides its primary task, with the help of an internal stopper protects the drivers from earwax and also serves as a sound signal splitter. To tell the truth, I have never encountered such a comfortable and convenient tip.




On top is the RCX cable connector, a patented proprietary connection specifically designed for in-ear monitors and rated for 5000 connections. The twisted Satin Black 8-core 26x8 Awg cable is made of pure copper. It is extremely lightweight, flexible and good-looking. RCX connectors, L-shaped TRS 3.5 mm jack plug, splitter is made in the same style. The cable length is 1.2 meters. I suppose you can choose other connectors and cable lengths when ordering. It is intended to be worn exclusively behind-the-ear.




Another important point is the production time of your individualized earphones. Order fulfillment takes only five days! Friends, it's just a holiday!


As you already know, the model has a hybrid circuit and is based on a 4-way crossover and four drivers of two types: one dynamic (DD 6mm/Low) and three armature open type (Open BA Driver / 1 Ultra-high, 1 High, 1 Mid/Low).



So, well, we've got the kit, design and technologies sorted out, now let's move on to the most delicious part - go ahead and analyze the sound.




Sound impressions


Sound equipment: MyST DAC 1866OCU V.2, Lotoo paw Gold, iBasso DX240, DX300, iBasso 220 MAX, QLS QA-361, iFI iDSD Diablo, iFi Gold BAR & iFi xDSD Gryphon.

Before listening, the Bellos Audio X4  were burn-in for 80 hours.



I would label the sound of X4 as balanced, sustained in neutral-warm tones, with good transmission of the emotional component, high resolution, charming, velvety, expressive middle, smooth, going in line with the entire frequency range bass and a slight unobtrusive "sparkle" in the high-frequency range.


It is a smooth and sweet-voiced style where the focus is on the midrange and the lower and upper registers clearly interact with it, adding a balanced and melodic character to the sound.





The sound picture is painted with contrast, smoothness, sprawling stereo panorama, good instrument separation, texture, timbre, and meticulous rendering of fine nuances. Here, dynamics, euphony and neutrality combine to create exquisite sound images that shimmer to form a skillfully assembled, impressive audio landscape.




The bass is clear, collected, with articulate punch and good velocity characteristics. It is delivered in an extremely linear manner. There are no questions about the quality and quantity of its processing, it is in line with the rest of the frequency range. This is a well-crafted, comfortable and delicate performance. The focus is shifted a little towards the midbass, which takes on a fullness rather than size, displaying a smooth, charming mannerism and naturalistic rendering of textures. It's a bit leisurely, but precise and collected. The sub-bass area has a slight slump and complements the overall picture rather than fully participating in it.



The Mids in the X4 are the star of the whole show: smooth, smooth, harmonious and extremely natural. In the midrange, each musical image is endowed with its own tangible foundation. The register is at once solid, velvety and extremely detailed. Drive, emotion and dry neutrality are perfectly combined here. Every timbre, every vibration of the voice or the trembling of a string is conveyed naturally and deeply, naturally, smoothly and sonorously, without a hint of synthetics. Everything sounds true and clear, technical and extremely melodic.



High frequencies are reproduced accurately and harmoniously. Quantitatively, they are neither too much nor too little - there is no need for more, as, to my taste, the delicacy of the treble is only to the benefit of the whole picture. The register is transmitted quite clearly, with a little unobtrusive "sparkle", but without excessive sharpness and distortion. It diligently contributes to the overall work, only slightly embellishing the final sound of the headphones. It's an attractive and correct manner, with good articulation, delivered in an easy, graceful and comfortable manner.




The X4's soundproofing is average, no worse or better than most earphones.




In terms of musical genre preferences Bellos X4 are not capricious. They play both instrumental music, jazz, electronica and any kind of rock with their expressive "coloring". I am sure that this model will be perfect for instrumentalists, vocalists and audiophiles alike.






In my opinion, the Bellos Audio designers have done their job brilliantly - CIEM have turned out just right! X4 is a model with a stylish, austere design, good build, extraordinary comfort and neutral, detailed and extremely melodic sound.


In my opinion, such an sound signature can satisfy the demands of a wide range of music lovers and professional musicians. Here we should also add the production of the order in just five days (after receiving impressions) and a two-year warranty on the product.


The X4 CIEM can be ordered from the official website for $999. Considering the unprecedented ergonomics of these in-ear monitors, their excellent appearance, the level of assembly and, most importantly - high quality and attractive sound, I consider the cost of these CIEMs to be fully justified.





Sound, ergonomics, design, build quality, materials, speed of order fulfillment, price



No (not at this price)

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