Sound impressions
With a rated sensitivity of 116 dB/mW and an impedance of 16Ω at 1kHz, X4 is very easy to drive. They’re about as sensitive as the FIR Frontiers, if you’re familiar with those, which means you can drive X4 off just about any device, including a phone, with no external amping required.
I put X4 though my usual playlist of test tracks, which covers a wide range of genres but avoids aggressive music like hard rock and metal. Testing was done primarily with HiBy’s RS8 (reviewed here), but also the new HiBy R8 II (reviewed here), to get a sense of how X4 adapts to different source tunings.
Tonally, I hear X4 to have a relaxed, warm-tilted tonality, with weighty but well-controlled bass, a smooth, neutral midrange, and laid-back highs with just enough sparkle and a slight mid-to-upper treble bump to keep things from sounding too flat. While the tuning is steered towards fatigue-free monitoring and mixing, as an audiophile it’s exactly the type of tuning that appeals to me most, especially for longer listening sessions.
Despite its smaller-than-average dynamic driver, X4’s bass delivery goes to show that size doesn’t always matter when it comes to low frequency performance. With a lifelike, accurate instrumental timbre, X4 also has plenty of punch to reproduce both the kick of a drum and the drop of a synth. This is a physical but also clean-cut bass that underpins the mids and highs but doesn’t intrude on either, and as such probably won’t be enough to satisfy die-hard bassheads.
For instance, listening to the kick drum in the intro of the Eagles live rendition of Hotel California feels like I’m hearing them in a studio – clean and accurate but without the live stadium boom. Then, switching to the faster electronic drums in Alphaville’s Sounds Like A Melody, X4 keeps pace with the beat while delivering a deep and satisfying punchline throughout.
There’s an ever-so-slight attenuation in the sub-bass, possibly a factor of the reduced isolation of the In-Air Canal design, but more likely a tuning tradeoff that purposefully places more focus on midbass fullness, and infuses the lower midrange with a hint of warmth too. I can feel the extra note weight in Feist’s Tout Doucement, for example, which maintains plenty of detail in the bass notes despite the jazz-lounge thickness.
The midrange presents with the same smooth and effortless delivery as the bass, and despite an audible rise through the upper midrange, keeps vocals and instrument fundamentals close to neutral.
Male vocals are as chesty as you’d expect, but perhaps not as delineated away from some of the lower frequency backing instruments. Neil Diamond’s chesty drawl in The Jazz Singer’s Hello Again is as real and present as you’re likely to hear it, but lacks some of the contrast it might enjoy from an IEM with a larger bass-to-midrange cut.
Female vocals are similarly smooth, but there’s some resonance from the upper frequencies that gives a few recordings, like Ethel Cain’s Sun Bleached Flies, a slightly drier sheen, and make others, like Hannah Frances’s Keeper of the Shepherd, sound crisper than I’d like.
Still, on the whole I’d characterise the midrange as rich, lush and expansive. Yes, there’s an occasional edginess somewhere around the upper midrange, but I suspect it’s more a factor of certain recordings – combined with X4’s revealing tonality – rather than any wonkiness in the tuning.
Treble, to me, is one of the nicer parts of the X4 package. It extends very well, and offers just enough sparkle to keep things interesting while coming off as more relaxed.
There’s plenty of information in the treble, with the fine steel guitar strums in Nils Lofgren’s Keith Don’t Go sounding sharp and articulate as always, but it’s not a biting sharpness. There are also zero sibilants in Missy Higgins’ cover of Shark Fin Blues, a track that can be as deadly to the ear as the subject matter with the wrong IEMs.
X4 is by no means a dark-sounding IEM; on the contrary, it has the ability to come off as a touch bright with some music, but mostly because of the vocal crispness I mentioned earlier. Overall, the measured balance of X4’s tonality makes it, for me, the consummate all-rounder. It has a gentle, easy-listening sound that draws you into almost any type of music, revealing just enough to make things interesting, but never too much to fatigue.
Technically, X4 is almost as impressive as its tuning. While I consider X4’s stage to be expansive, it’s wider than it is deep and not particularly tall.
The stereo separation in my go-to stage test, Yosi Horikawa’s Bubbles, passes with flying colours, but the dropping balls are mostly arranged in a long, wide row, perfectly imaged and separated, but only moderately layered. Then, listening the psychedelic synths in Lana Del Rey’s magnificently trippy Venice Bitch gives the different musical elements a sense of precise separation with very little if any overlap, which renders them flatter than I’m used to.
Still, X4 easily manages to keep up with busy passages by virtue of its excellent sense of organisation, so a track like Daft Punk’s Contact, which crescendos in a crazy overload of sound effects and musical overlays, never descends into chaos. It’s quite remarkable how well X4 articulates complexity and keeps instruments and vocals separate from each other, but then, this is an IEM designed to do just that.
There’s a decent amount of resolution in here too, though don’t expect X4 to compete with detail monsters and all-BA flagships, so detail addicts beware. That’s not to say X4 is blunted when it comes to detail retrieval; far from it. But it’s an IEM that doesn’t push details too far forward, and never in your face. In my opinion, it’s this characteristic that gives it the relaxed presentation I spoke of earlier.
While X4 is also reasonably dynamic, it doesn’t have quite the same refinement of the super flagships like FIR’s Frontiers. As such I find it to be a more pleasant listen at slightly lower volumes than my usual, especially with poorer recordings.
While it might seem that I’m not exactly singing X4’s technical praises, it’s actually a very solid technical performer, more so than its price suggests, and I’d wager more than enough for taking out on stage or into the mixing studio. But technical performance is, for me, secondary to what it offers the enthusiast listener: that smooth, rich tone that casts a warm glow on most recordings and adds a touch of romance to the music I listen to.
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