Bellos Audio X4: An Engineer’s Perspective – A Custom In-Ear Monitor Review

Select Comparisons

64 Audio A6t ($1299)

What mainly separates the A6t and X4 is delivery. The A6t is a harder-hitting IEM with punchier highs and more elevated lows, while the X4 is gentler and refined. Tonal differences aside, this disparity is down to technical performance too. The A6t has limited dynamic range, meaning it’s punchy all the time. The X4 is far more capable of setting its energy level in accordance with the track, making it a more accurate engineer’s monitor. Imaging is the same. The A6t’s stage stays within the head, while the X4 easily spans outside it. I feel the A6t is more ideal if you’re a stage performer looking for a more vibrant, exciting in-ear to grip your attention, while the X4 is for the engineer looking for a wider, macro and less-biased view of the mix they’re working on. Lastly, it shouldn’t come as a surprise that I consider the X4 the far comfier custom with its In-Air Canals.

64 Audio A18t ($2999)

Against the X4, the A18t also comes off more v-shaped; lifted lows (and low-mids), plus sharper highs. It also doesn’t have as much upper-mid presence as the X4, which tames, say, the upper registers of the piano, the electric guitar or the tenor sax compared to the kick drum or hi-hat. In imaging, the two are quite close. I venture to say the X4 has a bit more width, and its stage feels less full because of its comparatively relaxed lows and low-mids. You’ll hear more texture across 100-1000Hz on the A18t, because it pushes those frequencies a bit further forward. But, the X4 wins out on sheer top-end extension with its airier, blacker background. You can’t go wrong with either, in my opinion. It’ll come down to whose tone you find easier to work with, even if the X4’s far lower price and comfier In-Air Canals give it an inherent advantage.

JH Audio Layla ($2199)

The Layla and X4 deliver music in a very similar way; relaxed and unforced in a surround sound setting. Both excel at even, out-of-head imaging that instantly lets you know when you’ve placed an instrument too far forward or too far back. Where they mainly differ is tone, especially up top. Compared to the X4, the Layla is far more relaxed in its low- and upper treble. The former gives it almost-diffuse transients, where cymbals, hi-hats and sibilants don’t have as much of an edge as they normally should. They come off slightly out-of-focus. And, it’s also light in air. There isn’t as much light illuminating the stage and the outlines of instruments within it. Again, like the A18t, this is a matter of preference. The Layla is stronger if you prefer a mellower, more diffuse sound, and the X4 is more ideal if you prefer tighter, better-outlined instruments and a stronger sense of air.

JH Audio Sharona ($2499)

Of the in-ears here, the Sharona is most like the X4 tonally and technically. Like the Layla, these two have that laidback, unbiased, macro view of music in common. But, the Sharona’s tonality is much more akin to the X4’s. The main differences I hear are heavier lows and calmer high-mids on the JH. In a way, it’s the X4’s earthier, less dainty sibling. Technically, the Sharona is notably ahead. It resolves textures to a higher degree, and it’s got a blacker, deeper background, which makes its notes more 3D. This is partly due to its deeper stage too. So, if you have the cash, the Sharona is the stronger mastering IEM, simply due to how much detail it’s capable of extracting. But, the X4 is one heck of a second option at less-than-half the cost, along with tech like In-Air Canals and ATOM, which, I can say from experience, come in really handy when you’re mixing for long stretches of time.


Bellos Audio’s X4 is the engineer’s in-ear. At $999 MSRP, not only are you getting a monitor that performs far above its price tag, but also an experience tailor-made for the working pro. From its 5-day turnaround, to its nanometer-precise build, peerless comfort, robust connector system and repairability, it’s astounding that sound quality is just one of the many boxes it deftly ticks. While IEMs are often far down a musician’s shopping list, and a grand is more than many are willing to spend, if you’re gonna splurge, ‘might as well do it on the one that’ll give you the utmost for your money. As their flagship, the X4 is a perfect personification of Bellos Audio’s ethos: No needless frills or bells-and-whistles; just an exceedingly capable and reliable tool that makes you better at what you do.



Picture of Deezel


Church-boy by day and audio-obsessee by night, Daniel Lesmana’s world revolves around the rhythms and melodies we lovingly call: Music. When he’s not behind a console mixing live for a congregation of thousands, engineering records in a studio environment, or making noise behind a drum set, you’ll find him on his laptop analysing audio gear with fervor and glee. Now a specialist in custom IEMs, cables and full-sized headphones, he’s looking to bring his unique sensibilities - as both an enthusiast and a professional - into the reviewer’s space; a place where no man has gone before.


Leave a Reply

Your email address will not be published. Required fields are marked *

Recent posts