I analyzed U18s sound performance paired up with LPGT while playing a variety of test tracks, such as Agnes Obel “The curse”, Sandro Cavazza “So much better” (Avicii remix), C-Bool “Never go away”, Ed Sheeran “Shape of you”, Alan Walker “Darkside”, Galantis “Hunter”, Iggy Azalea “Black widow”, Indila “Boite en argent”, Dua Lipa “Love again”, Counting Crows “Big yellow taxi”, David Elias “Vision of her”, and Michael Jackson “Dirty Diana”. By force of habit, I let U18s play for about 4 days in a loop before I started analyzing the sound. I used stock SpinFit eartips and stock cable in my analysis.
U18s has a fuller body warmer detailed tonality. The sound is smooth, natural, and quite detailed, not revealing like in U18t but rather clear and detailed in upper mids and treble. The lower frequency range has a fuller body with a warmer tonality and surprisingly good bass impact for BA drivers. But you have to pay close attention to which apex module you are using because they leave a noticeable effect on tonality and signature. In most of the 64 Audio IEMs with removable apex I prefer to use M15 because it has the perfect balance between bass impact and soundstage expansion, keeping in mind “15” referring to 15dB isolation. However, when I started to listen to U18s with a default M15 module, I found a lack of definition in lower mids.
As expected, going between MX, M15, and M20 changes the soundstage expansion, with MX and M15 being wider due to less isolation and M20 being narrower. But in terms of tonality, upper mids and treble sounded quite similar, while bass and lower mids did change. MX gave bass a more neutral quantity, making signature more balanced, with more focus on natural detailed mids and natural clear treble. Not your typical tia airy sparkle, but instead, a smoother well-defined treble. Moving up to M15, bass gained impact and rumble, but the decay of bass notes extended and blended in with lower mids. It wasn’t bleeding into mids, but rather blending in a way that caused bass to lose its articulation and definition.
Then, I decided to switch to M20 and had a Eureka! moment. I did notice a trade-off with soundstage width shrinking down a bit. It was still above average but less expanded in comparison to MX and M15 modules. The sub-bass was as deep and had the same amount of rumble, maybe even a little more than when compared to M15. Mid-bass punch was stronger and faster, not basshead overwhelmingly strong, but just enough to tilt the scale of balanced sound sig into a slightly L-shaped territory. But the biggest benefit was a better separation of bass from lower mids. With M20 I hear the decay of bass notes to be shorter, giving bass more control and better definition. And with that, lower mids gained more clarity.
Now, with all this said, I still consider overall sound signature to be balanced (W-shape) because regardless of the bass impact it comes through with a noticeable quantity of deep velvety sub-bass rumble and punchy mid-bass impact, mids/vocals are not recessed, despite being natural, organic, and better than expected layered, and treble is well defined, clear, and actually extended without being too bright, crisp, or too airy.
I hear the overall soundstage to be above average, and as already mentioned, it gets wider with MX and M15 modules. But still, you get more depth/height rather than width when analyzing U18s. Typically, I find positioning and imaging of sounds to be better when tonality is more revealing. Don’t get me wrong, I don’t find anything wrong with accuracy of instruments and vocals placement when listening to U18s. But it was easier to pin-point sounds in less busy and more instrumental tracks while got a little more complicated in busy multi-layered tracks where I had to focus harder to zero in on some instruments. I do want to add, this was relative to M20 module, while switching to MX gave instruments and vocals more room to breathe. It was easier to pin point everything, but I was missing bass impact with MX, a trade-off you have to keep in mind.
In more details, bass is very responsive to apex module selection and I think many will prefer to go either with MX or M20, or maybe I’m just projecting my own preference. MX will give you a neutral bass impact, you can still hear the rumble and the punch, but the impact scaled down. M20 gives you a nice authorative slam, not an overwhelming basshead level but enough to cut through any serious EDM track with a strong rhythm. When you are listening to less aggressive music with natural instruments and no kick drums, bass comes into play with a deeper rumble to give instruments more natural fuller body tonality. And as I mentioned before, I found stronger impact with M20 to give bass more control and better articulation.
Mids and treble are natural, smooth, detailed, balanced, never falling behind the bass even with M20 module. You get a better definition and more forward presentation with MX module which puts more focus on mids. With M20 presentation of mids is less forward but still with enough focus. Mids/vocals are clear and natural, there is some layering, not as much as you would hear in more revealing tuning like U18t, but still enough to appreciate the expansion of vertical dynamics where the sound never felt compressed. Treble is clear and detailed, not crisp or sparkly but extended and with a natural airiness.