I would like to thank Stealth Sonics for providing the demo units for this tour and Jackpot77 of Audio Primate for getting me on board.
Stealth Sonics is a fairly new player in the IEM market-based in Singapore, I've not heard about them until recently when Jackpot77 of Audio Primate introduced me to their lineup. The U4 is their midrange offering featuring 4 balanced armature setup in a 4-way crossover. Their design is quite bold and unlike anything I've seen before, with swappable faceplate.
In the box:
Build quality and accessories:
Let me preface this a little, oftentimes, we associate quality with weight, if something is reassuring the buyer it's solid and that he got his money worth, which often isn't the case but it definitely is something we think about.
Having said that, the U4 is light, very light. It feels as if there's nothing inside. The build itself is solid and doesn't feel like it will break, but the sheer weight of the U4 makes them feel cheap. It's understandable this is to help with comfort but it doesn't scream quality.
The case albeit big, is well made, has more than enough space to fit all the accessories inside and the addition of the carrying pouch means you can use that when you don't need the whole case.
The cable is nice and light doesn't tangle much and has barely any microphonics.
The swappable faceplates, while they don't differ sonically, it gives at least a bit of customisation to those who like/dislike carbon fibre.
Fit and comfort:
The U4 is on the larger side, and while light, can prove a bit difficult to use for people with smaller ears. However, for others it's very comfortable, the almost nonexistent weight makes them disappear after a while even though they stick out of the ear a fair bit.
A warm, relaxed and smooth signature. Focusing on bass and fatigue-free listening.
When first listening to the U4 I thought it has a dynamic driver inside, the bass is impactful, rich and woolly. Unlike most BA IEMs which have quite a dry and "quick" presentation, the U4 gives the bass a slight resonating quality which helps make the bass more natural and fun to listen to. Technically the bass has a very good extension with good detail and texture.
The midrange is smooth and has quite a natural warmth to it, instruments sound full without adding too much thickness or significant loss in detail. The detail is still there but you have to listen to it. On songs like "Fleetwood Mac - The Chain" the vocals (especially female) are sweet and inviting rather than being perfectly accurate tonally. The overall timbre again while not being perfectly accurate helps the U4 maintain it's smooth and musical presentation.
The treble is the only drawback of the U4 to me, while it has a decent amount of clarity and air it feels lacking in extension. This isn't as big of an issue due to the generally relaxed nature of the U4 but should be noted. Otherwise, the treble follows the bass and midrange in its smooth and non-fatiguing presentation and warmth. For me, it lacks a bit of bite especially when it comes to cymbals.
Imaging and soundstage:
The imaging is good but separation feels a little lacking which can partially come from the presentation of the U4. The smoothness can blend the instruments together a little too much at times. The stage has decent depth and average width, bass extension and presentation largely help with the former.
The Stealth Sonics U4 is definitely an interesting IEM, what it loses technically it gains with natural and pleasant frequency response and presentation. I would love if Stealth Sonics could make them smaller and improve the fit especially for people with smaller ears. I can definitely recommend the U4 with the caveat of knowing what to expect. I'm quite looking forward to more IEMs from Stealth Sonics.