FiiO BTR11: power output and what it will drive

The FiiO BTR11 is a Bluetooth receiver at $36. It delivers 30 mW into 32Ω and 3.0 mW into 300Ω, which ranks it 263 of 280 for raw power among the sources in this database.

Measured at 100 dB SPL it has comfortable headroom on 411 of the 571 dynamic and planar headphones catalogued here, enough but not generous on 113, only marginal on 29 and not enough power for 18. Power is published at 16Ω, 32Ω, 300Ω; the rest of the table is derived from those figures.

The manufacturer publishes 45 mW into 16Ω, 30 mW into 32Ω, 3.0 mW into 300Ω. Everything else in the table above is worked out from those figures, and this table says which is which.

Derivation holds output voltage steady between and beyond the published loads rather than output power, because that is what an amplifier actually does. The full method is written up here.

Source: fiio.com.

Ordered from easiest to hardest to drive. Headroom is measured at 100 dB SPL, which is louder than almost anyone listens — a small negative number means the source still plays loud, just without reserve for peaks.

These figures come from each manufacturer's own sensitivity rating. A handful of planars — the HiFiMAN Susvara and HE-6se and the Abyss AB-1266 in particular — are widely reported to need far more than their published sensitivity implies, so treat a bare pass on those as optimistic rather than settled.

At 8.0 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 36 dB SPL, which you will hear between tracks and in quiet passages.

At 0.5 Ω output impedance, the one-eighth rule says this source suits headphones of 4.0Ω and above. 1 of the 571 models here falls below that. The one model below that line is the Symphonium Titan, and the mismatch tilts the frequency response audibly rather than subtly.

The rule is a rule of thumb, not physics: a source impedance below one eighth of the headphone's keeps the interaction under about 1 dB. The checker works it out for any pair.

Or put any two side by side in the source comparison tool, or run your own headphones through the amplifier matcher. Or see every FiiO source in the database, and how much of what this site says about them came from FiiO’s own documents.