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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 planar-magnetic in-ear that pulls apart dense recordings with speed and detail and can run balanced from a 4.4mm source, choose Letshuoer S12; if you need a stage-ready reference monitor with stronger sub-bass, passive isolation and a friendlier 3.5mm setup, choose NFACOUS NM20.
• Letshuoer S12 — biggest strength: a 14.8mm planar magnetic driver with 102dB/mW sensitivity, so it reaches reference listening levels from small dongles and portable players while staying quick and detailed. Biggest trade-off: it ships with a 4.4mm balanced plug in this version, which not every phone or laptop jack will accept without an adapter, and it has no noise control at all.
• NFACOUS NM20 — biggest strength: a single dynamic driver with a beryllium-plated diaphragm, dual acoustic chamber and NF ACOUS's Clutter Trap air-pressure tuning, plus 25dB of passive isolation — genuinely useful for stage and studio work. Biggest trade-off: 32 ohm impedance and a warm, bass-forward voicing mean it is less of a neutral microscope than a planar set.
• Who the S12 is for: listeners who want detail retrieval, a wide stage and a balanced cable path.
• Who the NM20 is for: musicians, engineers and audiophiles who need isolation, low-end weight and a cable that survives real work.
• My shorthand: S12 = analysis. NM20 = monitoring.
The S12 is built around a single 14.8mm planar magnetic driver, and that choice defines everything about it. Planar diaphragms move as a flat surface rather than a cone, which is why the S12 is described as having high detail retrieval, potent bass, crisp mids and clear treble. Its 16 ohm impedance and 102dB/mW sensitivity mean it does not need a powerful amp to get loud — a phone with a decent dongle, a tablet or a small DAC/amp combo is enough to drive it to reference levels. The claimed frequency response runs 20Hz to 30kHz.
Physically, this is a well-finished piece of hardware. The chassis is milled in a 5-axis process, with no hard edges across the seams and one continuous curve around the outline. It is lightweight enough to live in an everyday bag, and the matte finish adds some resistance to ear wax. Two vent holes on the sides of the shell relieve pressure inside the ear, which is the kind of detail that matters if you listen for hours at a time. The 0.78mm two-pin cable is detachable and woven from 128 strands of silver-plated monocrystalline copper — thick, soft, shielded and low impedance — and the earhook sits on the ear without twisting inward because the connector protrudes slightly from the shell. In this configuration the cable terminates in a 4.4mm balanced plug.
Accessories are generous: foam, standard and clear tips in S, M and L, a faux-leather case, a manual and a warranty card.
NFACOUS NM20: Who It's For
NF ACOUS started in 2014 building stage-customized in-ear monitors, and the NM20 reads like a product from a company that knows working musicians. It uses an integrated, electronically tuned dynamic driver with a beryllium-plated diaphragm, sitting inside a dual acoustic chamber design that manages air pressure. The company's Clutter Trap Technology balances pressure between the front and rear of the driver, which is the engineering behind its claim of a reference-class sound. Below 100Hz, the tuning is deliberately boosted — this is a monitor with real low-frequency weight, not a thin, clinical one.
The numbers tell you what to expect: 32 ohm impedance, 108dB sensitivity, and a frequency range of 20Hz to 40kHz. That higher impedance means it draws less current from a given source, and the 108dB sensitivity means it still gets loud easily from a phone or laptop. Crucially, it offers 25dB of passive sound isolation, which is the single most important spec for anyone monitoring on a stage, in a booth or on a noisy commute.
The shell is high-strength polycarbonate with a frosted surface, dressed with CNC-carved anodized aluminum parts — light, but with enough texture to feel considered. The nozzle is slightly curved to follow the second bend of the ear, reducing pressure on the crus helix, with a small protrusion that adds support on the concha. The 0.78mm two-pin connector has been redesigned for durability and easier connection while staying compatible with traditional cables. In the box: a storage box, four pairs of tips in XS, S, M and L, a 5N OFC cable, and a gold-plated 6.35mm-to-3.5mm adapter — a clear signal that a headphone amp or mixing desk is part of the intended workflow.
Buy the NM20 if you monitor, mix, or play live and need isolation plus low-end information you can trust. Skip it if you want maximum treble air and detail above all else, or you prefer a balanced 4.4mm connection straight out of the box.
Side-by-Side: Which Should You Choose?
• Best for detail retrieval and instrument separation → Letshuoer S12. A planar driver is the reason to pick it.
• Best for isolation in loud rooms → NFACOUS NM20. 25dB of passive isolation versus none on the S12.
• Best for balanced 4.4mm listening → Letshuoer S12. The supplied cable terminates in a 4.4mm plug.
• Best for plugging into a mixing desk or amp → NFACOUS NM20. The included 6.35mm adapter and OFC cable are built for that.
• Best for easy driveability from small devices → both. 102dB/mW at 16 ohm (S12) and 108dB at 32 ohm (NM20) are both efficient.
• Best for a wider treble ceiling → NFACOUS NM20 on paper. It is rated to 40kHz against the S12's 30kHz.
• Best for long-session comfort → a draw. The S12 uses pressure-relieving vents and a matte shell; the NM20 uses an anatomically curved nozzle. Both are designed for extended wear, just differently.
If I had to pick one, I would buy the NFACOUS NM20. In my opinion, its combination of 25dB passive isolation, sub-100Hz tuning, an amp-friendly adapter and a durable redesigned two-pin connector makes it the more versatile reference monitor for real work — stage, studio or a noisy desk. The S12 is the better pick if critical listening and detail are your priority and you have a 4.4mm source. But as a single do-everything monitor, I would take the NM20.
what is studio monitor headphones
Studio monitor headphones are headphones designed to reproduce audio as accurately as possible rather than to flatter it, so you hear what is actually in a recording. The NFACOUS NM20 fits this description with its reference-class tuning, dual acoustic chamber and 25dB of passive isolation. The Letshuoer S12 plays a similar role from a planar-magnetic angle, prioritising detail retrieval.
what are reference studio headphones
Reference studio headphones are a subset of studio monitors built to a neutral, repeatable standard so mixes translate to other systems. NF ACOUS describes the NM20's cavity design as providing a reference-class sound, and the S12 is engineered for high detail retrieval with crisp mids and clear treble. Both are wired, in-ear designs aimed at accuracy over colouration.
what are studio monitor headphones
The term covers any headphone intended for monitoring rather than casual listening — typically wired, with a flat-ish response and enough isolation to hear detail. The NM20 adds 25dB of passive isolation and a 6.35mm adapter for desk and stage use. The S12 leans on its 14.8mm planar driver and 20Hz–30kHz range for analytical listening.
can you connect headphones to monitor
Yes — studio monitors and mixing desks generally take a 6.35mm or 3.5mm output. The NFACOUS NM20 ships with a 3.5mm OFC cable plus a gold-plated 6.35mm adapter, so it connects directly. The Letshuoer S12 in this version uses a 4.4mm balanced plug, which may need an adapter for a standard monitor or phone output.
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