FiiO M21: power output and what it will drive

The FiiO M21 is a portable player at $599. It delivers 405 mW into 32Ω and 45 mW into 300Ω, which ranks it 119 of 280 for raw power among the sources in this database.

Measured at 100 dB SPL it has comfortable headroom on 552 of the 567 dynamic and planar headphones catalogued here, enough but not generous on 14 and not enough power for 1. Power is published at 16Ω, 32Ω, 300Ω; the rest of the table is derived from those figures.

The manufacturer publishes 480 mW into 16Ω, 405 mW into 32Ω, 45 mW into 300Ω. The rest of the table is worked out from those.

The balanced output is rated separately: 950 mW into 32Ω through the 4.4mm jack.

Derived rows hold output voltage steady, as an amplifier does (method).

Source: fiio.com.

Easiest to hardest to drive, with headroom at a 100 dB SPL peak.

At 2.0 µV of output noise, here is where that noise lands in the five most revealing in-ears in the database.

This one hisses. With the most sensitive in-ears in the database its own noise lands around 27 dB SPL, which you will hear between tracks and in quiet passages.

At 1Ω output impedance, the one-eighth rule says this source suits headphones of 8.0Ω and above. 15 of the 567 models here fall below that. Most of them are multi-driver in-ears, and the mismatch tilts the frequency response audibly rather than subtly.

Check any pair.

Copied from the makers’ own pages: fiio.com/m21_parameters, fiio.com/m21. Battery life is the maker’s own test figure.

Of the 280 sources here, 14 do everything the FiiO M21 does as a headphone output: reach 100 dB on every headphone it reaches, stay inside the one-eighth rule wherever it does and stay under the audible-hiss threshold wherever it does. The cheapest of them is the FiiO KA11 at $29, against this one’s $599 — $570 less, and a USB dongle rather than a portable player.

This counts the headphone output only; inputs, converters, the volume control and the build are outside it.

Compared with its closest rivals: vs Cayin N3 Ultra · vs FiiO JM21 · vs FiiO M11S · vs FiiO M15S · vs FiiO M17 · vs FiiO M23 · vs FiiO M27 · vs FiiO M33 R2R · vs Sony NW-ZX707.

Compare any two or match your own headphones. Every FiiO source here.