Bellos Audio X4

Bellos Audio, founded by Vlad and Bogdan Belonozhko, known as the Bellos Brothers, stands out in the pro audio industry for its innovative approach and dedication. With more than two decades of combined expertise, Bellos Audio is more than just another player in the audio market. It is a response to the increasing demand for high-quality audio products.

The company was born out of a partnership with FIR Audio with the aim of overcoming the challenges in the pro audio sector. The Bellos brothers embarked on a journey to understand and address these challenges, drawing on their extensive experience. They chose to break with conventional wisdom and start afresh, which enabled them to develop unconventional solutions and carve a distinctive niche for themselves in the industry.

This resulted in the X series, a series consisting of 3 different custom IEMs, namely the X2, X3 and X4. The latter represents the top model from Bellos Audio and I will now take a closer look at it in this review. Incidentally, this is my very first custom IEM, so I was all the more excited about the findings, especially with regard to wearing comfort. I had my ear impressions taken by a hearing aid acoustician who used the 3D scanning method. Both of my ears were scanned completely in around 15 minutes using a scanner, resulting in what is known as an STL file (a standardized 3D format) for each ear. I sent these two STL files to Vlad Belonozhko by e-mail and the production of my Custom X4 began. The advantage of the 3D scanning process is that you have the data digitally and no longer have to send ear impressions by post. In addition, the filling material in the ears is somewhat uncomfortable with the conventional method.



According to Bellos Audio, the X4 is equally suitable for musicians and audiophiles and should offer an exceptional sound experience. With an additional ultra-high driver and the company's own in-air canal technology, the X4 is said to offer an unprecedented level of clarity, detail and realism. In the following, I will shed light on how well this model achieves this.

The 4 in the name of the X4 stands for the use of a total of 4 drivers. 1 DD driver in the 6mm size is responsible for the bass range. The remaining BA drivers cover the midrange to super high frequencies.

Now we come to the groundbreaking technology that only Bellos Audio IEMs offer. Called In-Air canal technology, it enables the most comfortable custom IEM listening experience in the world. So comfortable that you feel like you have nothing in your ears! A perfect seal is maintained even when the wearer's jaw moves. Comfort and optimum sound quality are guaranteed. I will write a few more sentences about how it actually wears later. First, I would like to talk about the other technologies.

ATOM VENTING: A pressure relief system that improves the soundstage and reduces listener fatigue by dissipating air pressure in the sealed ear canals for a more immersive listening experience.

3D PRINTING: Bellos Audio 3D-printed matte shells: Thanks to patented 3D printing technology with nanometer precision, these custom IEM shells offer a comfortable, grippy fit and a matte finish that enhances both aesthetics and functionality.

RCX CABLES: A proprietary cable connection designed specifically for custom IEMs, offering exceptional durability with 5,000 connections and a standard 2-year warranty.

REMOVEABLE FACEPLATES: A revolutionary design feature that allows for quick and efficient repair of IEMs without the need to cut open the device, as the faceplates are secured with alloy steel screws.

MODULAR DRIVERS: Customized IEM enclosures designed to accommodate pre-assembled driver packages. This facilitates easy installation and removal of drivers without damaging the enclosure and ensures versatility and durability.

I was very excited the day UPS rang my doorbell and I held the parcel from the USA in my hands. Accordingly, I unboxed it quickly. As Bellos Audio mainly serves the pro sector, the packaging and presentation of the X4 is relatively simple without a lot of fuss and glitter. The packaging contains a black aluminum box engraved with the Bellos Audio logo and the name of the owner for whom the custom IEM was manufactured. In addition to the X4, the round aluminum box contains the connection cable, silicone ear tips in three different sizes (the middle size is pre-assembled), a cleaning brush and a sticker with the Bellos Audio logo. The connection cable has a 3.5mm plug for unbalanced operation. It is very flexible and soft and does not produce any microphonic effects. I would have preferred a balanced 4.4 mm connector. According to Vlad, as the audiophile sector is now becoming increasingly aware of Bellos Audio's IEMs, the company intends to offer a more appealing presentation in the future and perhaps also offer differently assembled cables or a choice of connectors. Instead of the RCX connector, you can now opt for the popular 2-pin connector on request, which makes it easier to change aftermarket cables.



The IEMs are very well made and, thanks to their non-slip and scratch-resistant outer layer, offer long-lasting pleasure without the housing leaving traces of use after a short time. Here you can see that these IEMs were designed as workhorses for the Pro sector. The silver Bellos Audio logo is engraved on the outside. On the inside, the initials of the owner for whom the X4 was specially manufactured. The nozzle, which is not really a nozzle at all, is a world first. It is oval-shaped and has a very shallow depth at the end of which the BA driver for the ultra-high frequency range is mounted. The very shallow depth of the end piece (which is no ordinary nozzle) means that the silicone eartips supplied fit perfectly. All the other eartips I have here slip off. You need eartips whose round connecting piece protrudes slightly from the rest of the casing. I can imagine that the eartips from Ortofon could fit here, for example. However, I didn't experiment any further because the eartips supplied fit perfectly, are super comfortable and I'm absolutely delighted with the sound of the X4. But one thing at a time!



Now we come to the most important thing, namely the comfort of the X4. I first turned the right IEM from the back to the front in my ear canal and then applied a little pressure from the outside of the housing and voila it fits like a glove! Then I did the same with the left side and the result is perfectly fitting IEMs like I've never experienced in my life. At first you notice them a little in your ear but after a few days you get so used to them that you even forget you have an IEM in your ear. There is absolutely no pressure and it is so comfortable. This is truly one of the biggest wow effects since I started listening with IEMs. I haven't had any other custom IEMs made yet, but it is known that with other custom IEMs, a movement of the jaw, e.g. when chewing, briefly loosens the seal and this leads to sound impairment. But I also often have this with universal IEMs when I eat something while listening. With the X4, there is actually no such impairment! You can chew, eat and the part still sits bombproof without loosening the seal. Ingenious!



So the X4 has already mastered the most important criterion of a custom IEM with flying colors! Now we come to the second most important criterion (at least for me) for the X4, namely the sound quality. And here I can already anticipate that it has exceeded my expectations! With an IEM that is primarily intended for musicians with a neutral tuning, you might initially think of a dead boring presentation, but this is by no means the case here. After hearing the first notes of the X4 on my iBasso DX320 MAX Ti, it immediately reminded me of the Custom Art FIBAE 7U. Just like the latter, the X4 offers a neutral tuning with a slightly warmer basic tone with enough punch at the bottom and smooth but very high-resolution trebles. Incidentally, the X4 is very easy to drive even unbalanced on the DX320 MAX Ti and you don't need more than gain level 1.



The bass range sounds very balanced and easy to hear from low bass to mid-bass. It places a slightly higher presence on the mid-bass range, making the overall presentation appear somewhat fuller. By using a DD driver, it sounds crisp with sufficient slam at all times, despite having slightly less quantity than a FIBAE 7U. It may not be the fastest and most detailed DD bass in the IEM range, but it is one of the most balanced where you won't miss anything in the long term without a direct comparison.

From the bass, I would now like to move on to the most outstanding feature of the X4 and that is clearly the stage imaging. An IEM in the 1000 USD class with this brilliant spatial imaging, the ingenious left/right separation and razor-sharp instrument separation is second to none. The IEMs I recently tested from Oriveti, which are in the same price range, can't even begin to achieve what the X4 conjures up here. Is it because of this super-short nozzle? I suspect that it also has to do with the fact that the sound is not bundled in a tube before it reaches the ear canal. In any case, great cinema at this point!

The bass is perhaps the weakest attribute of the X4, but everything else is at a very high level. Just like the mids. No boring neutral tuning, but a slightly warmer basic tone involves the listener in a carpet of sound with a great timbre. Acoustic instruments sound fantastic, as does the vocal reproduction, which is also perfectly centered in terms of stage technology, neither too direct nor too far away.

For me, the X4 is an absolute hit when it comes to the comfort of an IEM. I can't think of a better IEM in this respect. I will be testing other conventional custom IEMs in the near future to see how they perform. But on paper, it's already clear that only the X4 is immune to sound restriction caused by jaw movement. And who likes to sit on the sofa for hours with an IEM without eating anything? In terms of sound, the X4 also impresses me with its very coherent tuning and, above all, this grandiose stage presentation, which I never expected. This makes it the most comfortable all-rounder IEM I know! My clear recommendation for the price of 999 USD, which I think is abs