We compare products from their published specs and features; the verdicts below are our independent editorial opinions.
Updated: 2026-09-23 · 8 min read · Independent comparison
If you want a warmer, bass-forward in-ear monitor with a metal build and two cable options in the box, choose BASN Metalen 4; if you need a tunable, all-balanced-armature monitor for critical studio and stage work, choose KZ AS24. That's the short version. The longer version comes down to one question: do you want to shape your sound with your gear, or with a switch?
• BASN Metalen 4 — biggest strength: A four-driver hybrid setup (2 balanced armature + 2 dynamic drivers per earbud) that leans into enhanced bass and a balanced, "original" tuning, wrapped in a CNC-machined aluminum shell.
• BASN Metalen 4 — biggest trade-off: Wired 3.5 mm only, and the tuning is fixed — you get the sound signature BASN designed, not one you dial in yourself.
• KZ AS24 — biggest strength: An all-balanced-armature array with dedicated drivers for lows, mids, and highs/ultra-highs, plus an 8-level tuning switch so you can adjust the sound to the job.
• KZ AS24 — biggest trade-off: It's built for analytical listening and stage/studio monitoring, so listeners who want a big, easygoing low-end thump may find it less forgiving of poorly mastered tracks.
• Who BASN Metalen 4 is for: Musicians and everyday listeners who want a comfortable, noise-isolating hybrid IEM with strong bass and a durable metal body.
• Who KZ AS24 is for: Studio engineers, mixing hobbyists, and stage performers who want to tune their monitor and hear every layer.
The Metalen 4 is a hybrid design, and that's the whole story of its sound. Two balanced armature drivers and two dynamic drivers sit in each earbud, which is a combination chosen to bring both definition and low-end weight. The dynamic drivers handle the bass response, while the balanced armatures add detail. BASN describes the result as balanced and "original," and in my opinion that's a fair way to frame a hybrid: you get the punch and warmth of a dynamic driver without losing the clarity an armature brings to the mids and highs. If your listening leans toward drummers, bassists, and rhythm-forward music, this is the design you want to start with.
The build is where this one earns its name. The shells are carved from CNC aluminum alloy and then given a hard oxidation treatment, which is the process behind that finely textured, natural metal finish. That matters for real-world use. A metal shell resists the scuffs and cracks that plastic housings pick up in a gig bag, and it feels substantial without being described as heavy. The rounded tips and ergonomic shape, paired with both silicone and foam eartips, are aimed squarely at comfort and noise isolation. Foam tips in particular tend to seal deeply and cut down external noise, which is exactly what you want when you're tracking or playing live and can't afford to hear the room.
So who should buy it? Anyone who wants a wired, durable, bass-capable IEM they can use for practice, performance, and casual listening without thinking too hard about it. Who should skip it? If you want to fine-tune your frequency response, or you specifically want an all-armature analytical monitor, this isn't that product. The Metalen 4 gives you one well-chosen sound, not a menu.
KZ AS24: Who It's For
The AS24 Pro is the opposite philosophy. Instead of mixing driver types, it stacks balanced armatures — a lot of them. The design uses 31736 high-frequency and ultra-high-frequency array drivers for bright, clear treble, 29689 mid-frequency drivers for the middle of the spectrum, and a 22955 low-frequency driver for the bottom end. That matrix is the point: each part of the frequency range gets hardware dedicated to it, and the stated frequency range runs a full 20 Hz to 20,000 Hz. If you mix or master, that separation is useful, because it lets you hear what's happening in one band without it smearing into the next.
The manufacturing is genuinely interesting. KZ builds the acoustic chamber with DLP 3D printing at a claimed 0.01 mm error margin. In plain terms, that means the internal shapes that guide sound are made precisely enough to support a more deliberate acoustic design. It also explains the 19-ohm impedance and 116 dB sensitivity — this is an efficient, easy-to-drive monitor, which matters if you're plugging into a phone, a laptop, or a small interface rather than a dedicated amp.
Then there's the feature that defines the AS24 Pro: an 8-level tuning switch. Instead of swapping physical damping filters, you adjust a built-in electronic filter to change how the monitor sounds. KZ positions this as more precise and wider-ranging than traditional damping tuning, and the practical payoff is that one pair of earphones can be tuned to suit different jobs, different ears, or different tastes. That's a real advantage for anyone who can't decide between a neutral reference sound and something with more low-end emphasis.
The fit is designed around ear-canal data, so it's meant to sit snugly and securely, and the combination of resin and metal construction with silicone tips is aimed at strong isolation. KZ's own framing is that the seal is good enough to block out the world around you — which is exactly what a stage or tracking monitor needs to do. The silver-plated cable is there for conductivity and anti-oxidation, and KZ emphasizes that every part is serviceable rather than disposable.
Who should buy it? Producers, engineers, and performers who want to tune their monitor and prioritize clarity across the whole range. Who should skip it? Casual listeners who just want a warm, forgiving sound out of the box and don't want to think about switches.
• Best for bass-forward listening → BASN Metalen 4. The two dynamic drivers per earbud are there specifically to deliver enhanced low-end response.
• Best for critical mixing and detail work → KZ AS24. Dedicated armature arrays for lows, mids, and highs make it easier to isolate problems in a mix.
• Best for adjustable sound → KZ AS24. The 8-level tuning switch lets you change the signature without buying new gear.
• Best for a durable metal shell → BASN Metalen 4. CNC aluminum alloy with hard oxidation treatment is built to survive gig bags and daily handling.
• Best for cable flexibility → BASN Metalen 4. Detachable MMCX plus two included cables means easy replacement and easy switching between monitoring and normal playback.
• Best for easy driveability → KZ AS24. At 19 ohms and 116 dB sensitivity, it doesn't demand much power.
• Best for a simpler wired setup → BASN Metalen 4. One 3.5 mm connection, a volume-control cable included, no tuning decisions to make.
• Best for a secure, isolating stage fit → KZ AS24. The fit is engineered from ear-canal data with silicone tips for a snug seal.
If I had to pick one, I'd buy the KZ AS24 Pro. The 8-level tuning switch is the deciding factor for me — it means the monitor adapts to the work instead of the other way around, and the dedicated armature array for each frequency band is exactly what I'd want for critical listening. That said, if your priority is warmth and low-end weight rather than analysis, the BASN Metalen 4 is the more enjoyable pick, and its aluminum build and MMCX detachability give it real long-term practicality. Match the tool to the job. For studio and stage detail, I recommend the KZ AS24; for bass-forward everyday listening with a rugged metal body, I recommend the BASN Metalen 4.
FAQ
how to fit in ear headphones
how to clean in ear headphones
Wipe the nozzles and eartips with a dry cloth after use, and remove the tips periodically to clear any wax buildup. Neither the BASN Metalen 4 nor the KZ AS24 lists a waterproof rating, so keep liquids away from the housings and the MMCX connectors. The BASN's detachable cable makes it easier to clean the earpieces without stressing the connection.
how to open in ear headphones
There's no user-accessible opening on either model — the BASN Metalen 4's aluminum shells and the KZ AS24's 3D-printed acoustic chambers are sealed at the factory. Never pry them apart, because that would damage the drivers. What you can service is the outside: swap eartips, and on the BASN, detach and replace the MMCX cable if it wears out.
how to ear headphones
If you mean getting the left and right pieces oriented correctly, the key is the cable: the connector with the "L" marking goes in your left ear, and the one marked "R" goes in your right. On the BASN Metalen 4, route the cable over the top of your ear so the MMCX connection sits behind it. On the KZ AS24, push the bud in and twist slightly until it locks into the canal for a stable fit.
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