Bellos Audio X4
- Configuration: 1x DD / 3x BA
- RRP: $999
- Purchase: HERE
Introduction
The Bellos X4 first grabbed my attention when I saw a post in the Watercooler thread – it wasn’t even whatever was being said about them, and I can’t actually recall the comments – I was drawn to the minimal matt-black finish with a subtle but eye-catching logo. I had never heard of Bellos Audio before, but then established the link to Fir being a sub-brand that appears to focus more so on professional audio… curiosity spiked further, I proceeded to look up some reviews and the few that were out there in the wild were all incredibly positive. It would be fair to say that Fir Audio are well-loved and respected in this community, and I personally once-upon-a-time owned and loved the KR5, with all of this in-mind, I reached out to Bellos and spoke directly to Vlad who provided me a discount in exchange for a review.
A Bit About Me...
I worked in the consumer electronics industry for a large part of my career and have been passionate about music and technology for as long as I can remember. Even as a small child, I would ask my mum to put records on the turntable (Abba, Supertramp, and Planxty if anyone is curious).
My music preferences are very varied—anything from classical to techno, indie rock to jazz, and everything in between. In my early teens, I was a big fan of bands like The Cure and The Smiths (still am all these years later). I was bitten by the dance music bug in the early 90s, becoming passionate about genres like techno, house, trance, and IDM. I amassed a huge collection of records and CDs, DJing at various parties and occasional pirate radio station slots. Although it remained a hobby, I still own thousands of records, and my trusty Technics 1210 turntables are still going strong 30 years later—a testament to Japanese engineering!
I am not a professional reviewer, just an enthusiast who loves music and the devices we use to listen to it. Over the last few years, I have become obsessed with IEMs and related gear. I've bought and sold many, and kept a select few—ranging from the $20 Moondrop Chu to kilobuck sets like the Aroma Jewel, Oriolus' infamous 'Traillii,' UM Mentor, and various beloved single DDs. Through this exploration, I like to share my thoughts with the Head-Fi community, hoping they might be useful to others. However, remember that this is a highly subjective hobby, and your mileage may vary.
While I've been fortunate to own and try a variety of the TOTL sets on the market, I honestly enjoy lower-priced sets as much - especially as the gap continues to close, many much cheaper sets now offering significant value and further driving diminishing returns.
Bellos X4 Specifications
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)
Unboxing & Accessories
A rather understated affair – the X4 arrives in a small, simple box and upon opening you are immediately greeted with a metal puck style case and Bellos sticker. Not at the level of parent company Fir Audio, nor indeed many other sets in this price region but I suppose to be fair, the target market here has been audio professionals who I assume are less fussy than me and many other audio enthusiasts about these things!
From an accessory perspective I’ve nothing to complain about – you get a nice metal case, a cleaning brush and selection of tips which are all stored in the bottom of the case as per Fir Audio sets.
Cable
The universal differs somewhat to the system used to connect to the customs in that they use a standard 2-pin as opposed to the RCX used for customs. The connection feels pretty secure, but they do disconnect with relative ease. The cable itself matches the IEM aesthetic beautifully with a matt-black finish and while not the slimmest, it is quite light and with good ergonomics. It has a rubberish feel and coils in a nice compact bundle when not in use. Mine came with a 4.4mm connection which I assume is standard.
Design & Fit
A subjective statement here but I think these look and feel absolutely fantastic. I typically prefer a more understated design, and really love a matt-black finish so these tick both boxes. They feel incredibly robust and I expect they can take a bit of a beating – not that I ever treat my equipment badly, but with a set like this I feel confident bringing out and about to work, commuting, etc where they can be thrown in and out of bags without even scuffing, let along being damaged… this of course important too for professional use while touring and on-stage. In addition, when ordering the X4 you have the option to personalise your set to include text on both the inside of the shells and top of the case - I went for quite simply my initials which you will see below... 'DC'
I suspect most will choose the custom fit, and at time of purchase for me there wasn’t an option to choose a universal, but I requested directly via Bellos. I had some trouble finding tips to get a good fit, and after rolling numerous in my collection, I ended up using my trusty Symbio F – a go-to for many IEMs with smaller nozzles. With the Symbio, I get a wonderful fit with good isolation and due to the light weight of the X4, they are incredibly comfortable with absolutely no pressure build due to the excellent ATOM venting system.
Listening Impressions
Important to emphasise again here that my set is the universal version of the X4, not the custom that I suspect many will go for – I have yet to get ear measurements and as such had to go universal.
What immediately struck me with the X4 was a full-bodied and natural sounding presentation, heavily underpinned by a solid foundation of really excellent bass – perhaps not ‘bass-head’, but they must only be a smidgen below that level as there is ample in both sub and mid bass. The next striking element is the sense of imaging – while very distinct and pinpoint, it falls short of being
pristine and as such I get zero fatigue in longer sessions, the X4 goes in a much smoother direction. I can completely understand how these would be perfect for audio professionals who need to be able to clearly hear each component, but at the same time not suffer with fatigue during extended listening – likewise for audiophiles, where the benefit is also applicable. On the flipside, if seeking that absolute crystal-clear and pinpoint resolution, I would suggest looking elsewhere – the X4 are not the last word in resolution, but this has the benefit of the smoother tuning, so it really depends on what you are in the market for. What you get with the X4 is a set that will play any genre incredibly well, be it old or new recordings… I’ve often discovered how a more resolving set won’t handle lower-quality or older music too well, not an issue here with the X4.
The majority of my listening has been with the Sony NW-WM1AM2 and Aune M1p – the X4 are easy to drive and sound great regardless of source, not a fussy IEM by any means.
Bass
Hugely authoritative low-end with deep rumble and wonderful mid-bass slam that hits with a solid ‘large’ impact, plenty of quantity within all levels of the lower frequencies. The quality and again resolution takes a slight step back in favour of quantity, where impact definition for example has a softer edge to the slam – this being under somewhat focused scrutiny. Bass impact resonates in that sweet, central spot in my head and feels like it expands out to pretty much fill my entire skull, giving a nice visceral sensation.
Mid-range
Both male and female vocals sound authentic to my ears, and I wouldn’t say there’s a bias towards one or the other – they sit slightly forward, central and have ample weight that provides a realistic full-bodied presentation. Instruments in this region sound clear, natural and with a captivating warmth. There is a lushness in the delivery that I find can just bring a smile to my face, giving that warm and tingly feeling when the music calls for it. In spite of the warmth and lushness, we still have that clarity and as such never any sense of congestion in busier tracks.
Treble
The treble extends well and assists with an overall clear presentation. In my many hours of listening over the last month or so, I have had zero issues with any harshness. The ultra-high BA driver certainly captures the uppermost frequencies and delivers with ease, yet has a somewhat polite nature in that it never offends or overextends, even where tracks have more energy in this region... yet still crisp and sufficiently airy.
Technical
As noted, resolution is probably average or perhaps above at this price point, but I don’t see that as a negative – more a choice, as there are trade-offs both for lower and higher resolution in my experience, it really depends on what you are looking for. The soundstage is quite large, with a good sense of space expanding mostly in width, along with an airy overall presentation – within this, the imaging is clear and distinct along with very good layering.
Test Tracks
Joshua – Come On
This features on the truly wonderful Rae & Christian ‘AnotherLateNight’ from the early 00s, one of my favourites from this excellent series, and the further ‘Late Night Tales’ that came along after. This is a great example of how X4 presents across the FR – the bass is absolutely delicious when it makes an entry (impossible not to bring a smile to my face, and foot tapping!), vocals and instruments rendered with great accuracy and highly engaging. This is a relatively speaking older recording, yet sounds fantastic on the X4 – absolutely one of the selling points of this set.
Marine Eyes – Cocoon (modern classical)
While I can comfortably listen to, and very much enjoy modern classical on the X4, it is for genres like this that I would reach for a more resolving set as I do like the pristine detail – there are often subtle nuances that are best captured and as such more captivating with a more resolving set. That said, the lush and warm mids certainly provide an immersive experience and one could argue allows a more relaxing experience perhaps versus the type of focus that arises from those more detailed sets.
Aukai – Azure (modern classical)
Pretty much a rinse and repeat of my findings with the previous track, except for in this case the excellent low-end provides a really captivating sensation for the kick drums and occasional dips into the sub-bass region. Perhaps I’d ‘prefer’ a set such as Turii Ti here, but again there is nothing wrong and I could happily listen to this entire album and love every minute with the X4.
Keno – Flingair (downtempo)
This features on the excellent ‘Around the Corner’ from 2018 and is a real feel-good upbeat downtempo album… very reminiscent of the likes of Bonobo. A while since I’ve listened, and a pleasure to revisit for the purpose of this review. The X4 yet again demonstrates the ability to wrap me in a warm and engulfing embrace, a perfect match for this music – everything just sounds ‘right’ where there is ample bass; sub-bass is deep and visceral, mids are lush and captivating, and the highs sufficiently crisp to render a good sense of realism in percussion. It’s a mostly wide presentation in terms of soundstage.
Clark – Frau Wav (IDM)
Taken from the excellent ‘Body Double’ which is a recent reissue of the classic ‘Body Riddle’ from 2006 (I can’t believe how many years have passed since this was released…) on the legendary Warp label. Clark is a prolific producer of electronic music, and Body Riddle is one of my favourites – but they are all excellent. He is a master of producing complex, but captivating music, a hallmark typically being wonderful percussion. This sounds vast and at times even cavernous, especially how it evolves to a beautiful beatless segment around halfway through. For anyone that knows me, they will know IDM is one of my favourite genres and a key test for any IEM, X4 passes here with flying colours… 10/10.
FD – Top2Bottom (D&B)
Another important test genre, and one that quite a few IEMs can fail at for two reasons typically – not enough sub-bass, or too much upper energy. No such problem here… that DD digs deep and represents the lows perfectly – no issues up top either, but sufficient energy to ensure percussion is rendered well. X4 is a great choice for this genre.
The Beloved (indie rock)
Many will know The Beloved from their work of the early 90s, especially the wonderful ‘Sweet Harmony’. Possibly lesser known is their work from the 1980s, where the style was much more like The Smiths, Echo & The Bunnymen and others of that ilk. This features on the 1986 album ‘A Hundred Words’ and while the vocals certainly stand out as an obvious link to what they would become later on, they are otherwise unrecognisable being an indie rock band as opposed to the chilled electronic vibe they developed later on. Anyway, an interesting test of a completely different genre and a much older album. It does sound obviously ‘old’ where it sounds flatter and less dynamic but the X4 does as good a job as one could really expect and again being not ultra-resolving, this means also more forgiving of an older recording which I often find higher-end sets do a really bad job of due to how highly resolving they are. Leaving aside the flaws of an older recording, the X4 attributes are all immediately apparent, most obviously the excellent imaging.
Comparisons
An obvious set to compare is the FA19 that I recently reviewed, the new 10x BA flagship from FiiO which also retails for $999.
The FA19 is more resolving, and also leans neutral with more energy up top. The bass difference is apparent in terms of ‘BA’ versus ‘DD’ – while the FA19 perhaps digs a touch deeper in sub-bass, the obvious slam of the X4 DD is noticeable. You do get more detail with the FA19 due to the more resolving tuning across the 10x BAs, but this also means less forgiving for some genres. I find the FA19 better suited to modern and well-produced recordings for the most part, and a set I love to listen to ambient or modern classical music with – also excellent for female vocals.
Conclusion
I feel like the X4 is the sort of set that could accompany me on a mountain trek or some other outdoor excursion – knowing that they can comfortably take a bit of a beating, they are light and comfortable for hours of listening, and importantly, I know I can throw absolutely any genre at them and they will perform with ease, offering a warm and embracing experience… Speaking of which, I wrote a lot of this review while on holiday in the mediterranean, an area near where we were staying had beautiful clear water where an abundance of sea-life, rocks, seaweed etc was clearly visible, and with wonderful heat from the sun – it made me think of the analogy here with the X4 whereby you’ve got that embracing warmth, yet still excellent clarity to hear every nuance of the music... back in Ireland now sadly with pretty terrible weather!
The X4 is a solid all-rounder, adding a new element for me in as far as how incredibly robust they feel. The Fir DNA is evident in this offshoot brand and the only negative I can call out is the challenging fit with the universal – for this reason I knock off half a mark to conclude with a 4.5/5 review. Overall though an easy recommendation at this price point and my only regret is not getting impressions done so as to go custom… perhaps I still will at some stage.
