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We compare products from their published specs and features; the verdicts below are our independent editorial opinions.
If you want a musician-grade wired in-ear monitor with four drivers per earbud, swappable MMCX cables and a metal shell that survives daily abuse, choose BASN Metalen 4; if you need a lighter, ergonomic dual-driver IEM that plays nicely with USB-C phones and tablets out of the box, choose KZ Duet.
• BASN Metalen 4 — biggest strength: four hybrid drivers per earbud (2 balanced armature + 2 dynamic) in a CNC-machined, electroplated metal shell, with two detachable MMCX cables and a full accessory kit.
• BASN Metalen 4 — biggest trade-off: it's a wired-only, 3.5 mm design with a bulkier metal build and a spec sheet aimed at stage and studio users, not casual phone listeners.
• KZ Duet — biggest strength: a 10 mm + 8 mm dual-driver hybrid setup with precision crossover, up to 36 dB of passive noise isolation and a USB-C to 3.5 mm adapter with built-in DSP and 4 EQ modes.
• KZ Duet — biggest trade-off: a plastic enclosure with fewer drivers and no detachable cable system, so it's less of a long-term upgrade platform.
• Buy BASN Metalen 4 if you're a singer, drummer, bassist or detail-chasing listener who wants maximum driver count, metal durability and cable flexibility.
• Buy KZ Duet if you want an easy, comfortable everyday IEM for gaming, travel and USB-C devices without fussing over adapters or cables.
The Metalen 4 is built around driver count and control. Each earbud carries two balanced armature drivers and two dynamic drivers — four per side, a hybrid array that BASN says adds definition, detail and enhanced bass while keeping the frequency response balanced. The rated range runs from 16 Hz to 25,000 Hz with 16 ohm impedance and 108 dB sensitivity, which tells you this is a low-impedance, easy-to-drive IEM that a phone or a small interface can push without strain. That combination — armatures for articulation, dynamics for low-end weight — is exactly what a bassist or drummer wants when they need to hear their own instrument clearly inside a loud mix.
The design story matters just as much. The shell is CNC-crafted metal with electroplating, which BASN frames as corrosion resistance and protection against surface wear — a real consideration if your gear lives in a gig bag, gets shoved into a pocket between sets, or sits on a drum riser. The earpiece shape is a rounded tip, ear placement is in-ear, and the finish is Gloss Black with a matching metal carrying case. Noise control is handled through sound isolation rather than active circuitry.
What really separates it is the kit and the MMCX detachable system. You get two cables: a 4.9 ft OFC silver-plated audio cable and a fiber cable with an inline volume mic. Both detach at the MMCX connector, so a damaged cable is a replacement rather than a death sentence for the whole pair. Add S/M/L tips plus memory foams, a T-shirt clip, velcro strips, a cleaning brush, a 1/4" adaptor and a 12-month warranty, and you have a package that reads like a working musician's toolkit. Controls cover call, voice and music functions via touch on the wired controller.
Who should skip it? If you mostly listen from a USB-C phone with no headphone jack, or you want the lightest possible thing in your ears for a commute, the metal build and dual-cable setup are more than you need. This is the pick for someone who treats IEMs as equipment.
The Duet takes the opposite approach: fewer drivers, smarter integration. It uses a 10 mm plus 8 mm dual-driver hybrid arrangement with precision crossover technology. KZ's claim is specific and sensible — deep, resonant bass without muddiness, with vocals and instruments coming through cleanly. The 8 mm driver size is listed in the measurements, and the overall tuning is pitched as a balance between gaming and musicality rather than a flat studio reference.
The headline feature for most buyers is connectivity. The Duet ships with a USB-C to 3.5 mm adapter with built-in DSP and 4 EQ modes, and KZ lists compatibility with a long roster of USB-C devices — iPhone 15/16/17, iPad, Galaxy S24 through S20, Flip and Fold, Tab S10+ and S9, plus Google, Motorola, OnePlus, Nothing phones, tablets and laptops. That adapter is the reason this is a "convenient for travel" IEM: you can plug into a modern phone that has no 3.5 mm jack without hunting for a dongle.
The 3.5 mm jack is still there for anything with a standard headphone output, so it covers both worlds. Noise control is passive — sound isolation and passive noise cancellation, with KZ claiming up to 36 dB of noise blocked. For a train, a plane or a noisy gaming setup, that's the number that actually matters. Fit is handled by an oblique angled earpiece designed to match the ear canal naturally, with two sets of ear tip sizes included, which KZ says keeps them in place during exercise or travel. The enclosure is plastic in Black, keeping the weight down, and the warranty is listed as 1.
Who should skip it? If you want a metal shell, detachable cables you can upgrade, or the maximum driver count for critical listening, the Duet's plastic body and fixed cable make it a closed system. It's a superb everyday companion, not a modular platform.
Side-by-Side: Which Should You Choose?
• Best for stage and studio work → BASN Metalen 4. Sound isolation, inline volume mic cable, T-shirt clip and 1/4" adaptor point straight at performers.
• Best for USB-C phones and tablets → KZ Duet. The included USB-C to 3.5 mm adapter with DSP and 4 EQ modes is the deciding feature.
• Best for durability and repairability → BASN Metalen 4. CNC metal shell with electroplating plus detachable MMCX cables you can swap or upgrade.
• Best for comfort and light weight → KZ Duet. Plastic enclosure, oblique angled fittings and two tip sizes aimed at staying put during exercise.
• Best for gaming → KZ Duet. The tuning is explicitly framed as a balance of gaming and musicality, with up to 36 dB of isolation to cut room noise.
• Best accessory package → BASN Metalen 4. Two cables, memory foams, cleaning brush, velcro strips, clip, adaptor and a metal case.
• Best for plug-and-play simplicity → KZ Duet. One 3.5 mm jack, one adapter, no decisions to make.
In my opinion, the BASN Metalen 4 is the one I'd buy if audio quality and long-term ownership are the priority. Four hybrid drivers per side, a metal shell that resists wear, and MMCX cables that can be replaced or upgraded make it the more serious piece of gear — and the included kit means you're not buying accessories on day one. The KZ Duet is the smarter choice if your phone is USB-C and you want a comfortable, isolating IEM that just works for gaming, travel and daily listening. Check the current price on Amazon for both before deciding, since the value calculation shifts depending on what's in your bag already.
how to clean in ear headphones
Remove the ear tips first and rinse or wipe them separately, then use a soft dry brush on the nozzle and mesh to lift out earwax and dust. The BASN Metalen 4 actually includes a cleaning brush in the box, and its MMCX cables detach so you can work on the earbuds without dragging the cable around. Never push liquid into the nozzle or the driver housing.
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Start with the medium tips, insert at a slight angle and twist gently until the seal feels snug but not painful, then swap to small or large if the seal breaks or your ears ache. The KZ Duet uses oblique angled fittings designed to match the ear canal and ships with two sets of tip sizes; the BASN Metalen 4 includes S, M and L tips plus memory foams, which often seal better in noisy rooms.
how to open in ear headphones
There's nothing to unscrew on either model — "opening" usually means removing the ear tips and, on the BASN Metalen 4, unplugging the MMCX cable from the earbud. Grip the connector body firmly and pull straight out rather than wiggling the cable, and never pry open the driver housing, which is sealed on both IEMs. The KZ Duet's cable is not detachable, so leave the shell alone and clean only around the nozzle.
how to ear headphones
If you mean which way they go in, the cable typically routes over the top of your ear and down your back, with the left and right markings matched to each side. Both the BASN Metalen 4 and KZ Duet are in-ear designs with rounded or angled tips, so a shallow insertion with a good seal beats jamming them deep. If one side sounds thin, the tip isn't sealed — try a different size before blaming the driver.
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