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If you want a wired in-ear monitor that leans into a bright, pop-forward tuning with strong passive isolation and a mic for calls, choose FEDAI TRN CS4; if you need a lighter, aluminum-built IEM with tunable nozzles, a thicker silver-plated cable and a bassier, smoother signature, choose Kefine Delci 10mm.
• FEDAI TRN CS4 — biggest strength: A 10mm dual-magnet dynamic driver paired with a silicon-crystal composite diaphragm, tuned toward pop with even frequency distribution and a soundstage that stays wide and dynamic.
• FEDAI TRN CS4 — biggest trade-off: The housing is polycarbonate rather than metal, and the included cable uses a 0.75mm 2-pin connector, so you are locked into that pin standard if you ever want to upgrade.
• Kefine Delci 10mm — biggest strength: A 10mm DLC+PU hybrid diaphragm in a dual-cavity structure, wrapped in CNC-machined aviation aluminum that keeps each earbud down to about 5.3g.
• Kefine Delci 10mm — biggest trade-off: The 0.78mm 2-pin interface and interchangeable nozzles reward tinkerers, but that same modularity means more small parts to keep track of.
• Pick the TRN CS4 if you want a simple, mic-equipped everyday IEM with heavy passive noise isolation.
• Pick the Delci 10mm if you want a lighter, more premium-feeling build with tuning nozzles and a beefier cable.
The TRN CS4 is built around a single 10mm dual-magnetic-circuit dynamic driver with a silicon-crystal composite diaphragm. What that combination tends to deliver in practice is a relaxed, atmospheric low end, a transparent midrange and strong high-frequency resolution. FEDAI describes the overall tuning as pop-leaning, and the frequency distribution as even — which is a polite way of saying nothing jumps out and stabs you in the ear. For someone who listens to vocal-driven pop, acoustic sets and general streaming, that is exactly the right target.
The physical design is where the CS4 makes its case for daily use. It uses imported eco-friendly polycarbonate for a glossy, translucent shell, and FEDAI notes that this rigid material helps suppress internal sound-wave reflection, giving the tone a warm, mellow character. The fit is described as ergonomic and snug, and the isolation numbers are the real headline: roughly 26dB of passive noise reduction when worn properly without music playing, and up to about 30dB while you listen. That is genuinely useful on a bus, a train or a shared office. The detachable 0.75mm 2-pin cable has a slot-protection design that guards the pins from breakage, and a mic option is available on this version.
Who should buy it: commuters, students and office listeners who want one wired IEM that seals out the world, handles calls and doesn't demand fiddling. Who should skip it: anyone who wants a metal-bodied earphone, or who already owns cables terminated in 0.78mm 2-pin and wants to reuse them. With 23Ω impedance and a 20Hz–20kHz range, it's easy to drive from a phone or a basic dongle — no amp required.
The Delci's driver is the interesting part. Kefine takes a 10mm dynamic driver and builds it from two materials: Diamond-Like Carbon for high-definition clarity up top, and PU for a lush, balanced low end. The result, per Kefine, is a smooth, non-fatiguing signature with real high-frequency energy and deep sub-bass extension. A dual-cavity driver design optimizes airflow inside the shell, which is what gives the Delci its wide soundstage and its impactful, rich bass. Kefine calls the presentation "atmospheric," and the numbers back up the intent — 108dB sensitivity, 20Hz–20KHz, and a low 26Ω impedance.
Then there's the tuning flexibility. The Delci ships with interchangeable nozzles, and Kefine includes six pairs of eartips in two styles: Bullet tips for bass and Bowl tips for transparency. Between the nozzles and the tips, you get real room to nudge the sound toward thump or toward airiness without buying anything extra. That is unusually generous for a wired IEM.
The build is the other half of the story. Each earbud is CNC-machined from a single block of aviation-grade aluminum and weighs only about 5.3g — roughly half what a die-cast metal earphone would weigh. The gunmetal anodized finish is described as scratch-resistant. The cable is a 1.2m dual-color design made from 164 high-quality copper wires, silver-plated, with a universal 3.5mm plug and a detachable 0.78mm 2-pin interface so you can swap it later. A hard-shell carrying case is included, and the warranty runs two years.
Who should buy it: listeners who want a light, premium-feeling metal IEM, care about bass depth, and enjoy tuning their sound with nozzles and tip rolling. Who should skip it: anyone who wants a mic for calls — this version is wired audio only — or who prefers a set-and-forget earphone with no extra pieces to manage.
Side-by-Side: Which Should You Choose?
• Best for passive noise isolation → FEDAI TRN CS4. Its 26dB (up to 30dB with music) isolation figure is the more commuter-friendly of the two.
• Best build quality and lightest fit → Kefine Delci 10mm. CNC aviation aluminum at about 5.3g per earbud versus a polycarbonate shell.
• Best for bass depth → Kefine Delci 10mm. The dual-cavity design and DLC+PU diaphragm are explicitly aimed at deep sub-bass extension.
• Best for tuning flexibility → Kefine Delci 10mm. Interchangeable nozzles plus six pairs of eartips in two styles give you more ways to shape the sound.
• Best for calls and voice chat → FEDAI TRN CS4. A mic version is available; the Delci is a straight wired earphone.
• Best cable out of the box → Kefine Delci 10mm. A 164-core silver-plated 1.2m cable is a more substantial stock cable than a basic 2-pin.
• Best for easy driveability → Kefine Delci 10mm. At 26Ω versus the TRN CS4's 23Ω, both are phone-friendly, but the Delci's 108dB sensitivity means it gets loud with very little power.
If I were buying for myself, I would take the Kefine Delci 10mm. In my opinion, the combination of a DLC+PU diaphragm, a dual-cavity bass design, CNC aluminum at 5.3g, a 164-core cable, tuning nozzles and a hard case is simply the more complete package for someone who listens critically and likes to adjust things. The TRN CS4 remains the smarter pick if your priority is blocking out noise on a commute and taking calls — its isolation and mic option are real advantages. But for pure sound-shaping flexibility and build, I'd go Delci. Check the current price on Amazon before you commit, since both are wired IEMs competing in the same space.
The Delci 10mm is the more bass-focused design on paper. Kefine pairs a PU portion in the diaphragm with a dual-cavity structure specifically to create impactful bass and deep sub-bass extension. The TRN CS4 is tuned toward pop with a relaxed low end rather than a boosted one.
No. This version is listed as a wired earphone with a 3.5mm jack and no mic. The FEDAI TRN CS4 is available with a microphone, which makes it the better choice if you take calls or game with voice chat.
Both are easy. The TRN CS4 is rated at 23Ω with 20Hz–20kHz, and the Delci is 26Ω with 108dB sensitivity and the same frequency range. Higher sensitivity means the Delci reaches higher volume with less power, but neither needs a dedicated amplifier.
Yes, but the connectors differ. The TRN CS4 uses a detachable 0.75mm 2-pin cable with slot protection, while the Delci uses a detachable 0.78mm 2-pin interface on its 164-core silver-plated cable. Make sure any replacement cable matches the correct pin size.
The FEDAI TRN CS4. FEDAI states it isolates around 26dB when worn properly without music, and up to roughly 30dB while playing. The Delci's aluminum shell is lighter and more premium-feeling, but the CS4's isolation is the more commuter-oriented spec.
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