The FiiO BTR5 2021 is a Bluetooth receiver at $109. It delivers 80 mW into 32Ω and 8.5 mW into 300Ω, which ranks it 228 of 280 for raw power among the sources in this database.
Measured at 100 dB SPL it has comfortable headroom on 482 of the 571 dynamic and planar headphones catalogued here, enough but not generous on 73, only marginal on 12 and not enough power for 4. Power is published at 16Ω, 32Ω; the rest of the table is derived from those figures.
The manufacturer publishes 90 mW into 16Ω, 80 mW into 32Ω. Everything else in the table above is worked out from those figures, and this table says which is which.
The balanced output is rated separately: 240 mW into 32Ω through the 2.5mm jack.
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.
| Load | Power | Status | How it was arrived at |
|---|---|---|---|
| 16 Ω | 90 mW | Published | the manufacturer publishes this figure at this exact load |
| 32 Ω | 80 mW | Published | the manufacturer publishes this figure at this exact load |
| 150 Ω | 17 mW | Derived | beyond the published loads, holding output voltage constant — which understates rather than flatters |
| 300 Ω | 8.5 mW | Derived | beyond the published loads, holding output voltage constant — which understates rather than flatters |
| 600 Ω | 4.3 mW | Derived | beyond the published loads, holding output voltage constant — which understates rather than flatters |
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.
| Headphone | Impedance | dB/mW | Needs | Headroom | Verdict |
|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 114.0 | 0.04 mW | +31 dB | Comfortable audible hiss |
| 64 Audio U12t | 12.6 Ω | 108.0 | 0.16 mW | +27 dB | Comfortable audible hiss |
| Shure SE215 | 17 Ω | 107.0 | 0.20 mW | +26 dB | Comfortable audible hiss |
| Moondrop Aria | 32 Ω | 107.1 | 0.19 mW | +26 dB | Comfortable faint hiss |
| Audeze LCD-X 2021 | 20 Ω | 103.0 | 0.50 mW | +22 dB | Comfortable faint hiss |
| Truthear Hexa | 20.5 Ω | 103.1 | 0.49 mW | +22 dB | Comfortable faint hiss |
| Sennheiser IE 200 | 18 Ω | 101.6 | 0.69 mW | +21 dB | Comfortable faint hiss |
| Sony MDR-7506 | 63 Ω | 106.0 | 0.25 mW | +22 dB | Comfortable faint hiss |
| Meze 99 Classics | 32 Ω | 103.0 | 0.50 mW | +22 dB | Comfortable faint hiss |
| Focal Clear MG | 55 Ω | 104.0 | 0.40 mW | +21 dB | Comfortable faint hiss |
| Philips SHP9500 | 32 Ω | 101.0 | 0.79 mW | +20 dB | Comfortable faint hiss |
| Focal Utopia | 80 Ω | 104.0 | 0.40 mW | +19 dB | Comfortable faint hiss |
| Meze Empyrean | 32 Ω | 100.0 | 1.0 mW | +19 dB | Comfortable faint hiss |
| Campfire Audio Andromeda 2020 | 9 Ω | 94.0 | 4.0 mW | +11 dB | Comfortable faint hiss |
| Etymotic ER2SE | 15 Ω | 96.0 | 2.5 mW | +15 dB | Comfortable faint hiss |
| AKG K371 | 32 Ω | 99.1 | 1.2 mW | +18 dB | Comfortable faint hiss |
| Audio-Technica ATH-M50X | 38 Ω | 99.0 | 1.3 mW | +17 dB | Comfortable |
| Beyerdynamic DT 900 Pro X | 48 Ω | 100.0 | 1.0 mW | +17 dB | Comfortable |
| Audeze LCD-2 Classic | 70 Ω | 101.0 | 0.79 mW | +17 dB | Comfortable |
| Grado SR80x | 38 Ω | 98.0 | 1.6 mW | +16 dB | Comfortable |
| Sennheiser HD 560S | 120 Ω | 100.8 | 0.83 mW | +14 dB | Comfortable |
| HiFiMAN Edition XS | 18 Ω | 92.0 | 6.3 mW | +11 dB | Comfortable |
| HiFiMAN Arya Stealth | 32 Ω | 94.0 | 4.0 mW | +13 dB | Comfortable |
| Dan Clark Audio AEON 2 Closed | 13 Ω | 90.0 | 10 mW | +9 dB | Enough |
| Audeze LCD-5 | 14 Ω | 90.0 | 10 mW | +9 dB | Enough |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 102.0 | 0.63 mW | +12 dB | Comfortable |
| HiFiMAN HE400se | 25 Ω | 91.0 | 7.9 mW | +10 dB | Comfortable |
| HiFiMAN Sundara | 32 Ω | 92.0 | 6.3 mW | +11 dB | Comfortable |
| Dan Clark Audio Stealth | 23 Ω | 90.0 | 10 mW | +9 dB | Enough |
| Fostex T50RP MK3 | 50 Ω | 92.0 | 6.3 mW | +9 dB | Enough |
| AKG K702 | 62 Ω | 92.9 | 5.1 mW | +9 dB | Enough |
| ZMF Verite Closed | 300 Ω | 99.0 | 1.3 mW | +8 dB | Enough |
| Sennheiser HD 650 | 300 Ω | 97.8 | 1.7 mW | +7 dB | Enough |
| Sennheiser HD 800S | 300 Ω | 96.8 | 2.1 mW | +6 dB | Enough |
| Beyerdynamic DT 770 Pro (250Ω) | 250 Ω | 96.0 | 2.5 mW | +6 dB | Enough |
| Audio-Technica ATH-R70X | 470 Ω | 98.0 | 1.6 mW | +5 dB | Enough |
| ZMF Atrium | 300 Ω | 96.0 | 2.5 mW | +5 dB | Enough |
| Abyss AB-1266 Phi TC | 50 Ω | 88.0 | 16 mW | +5 dB | Enough |
| Sennheiser HD 600 | 300 Ω | 91.8 | 6.6 mW | +1 dB | Marginal |
| HiFiMAN Susvara | 60 Ω | 83.0 | 50 mW | -1 dB | Not enough |
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 24 dB SPL, which you will hear between tracks and in quiet passages.
| In-ear | Impedance | Sensitivity | Hiss level |
|---|---|---|---|
| Tanchjim EA FORCE | 17 Ω | 137.7 dB/V | 24 dB SPL |
| Shure SE846 | 9 Ω | 134.5 dB/V | 20 dB SPL |
| Campfire Audio Clara | 13.3 Ω | 134.1 dB/V | 20 dB SPL |
| 64 Audio Fourte | 10 Ω | 134.0 dB/V | 20 dB SPL |
| Shure SE535 | 36 Ω | 133.4 dB/V | 19 dB SPL |
At 1.0 Ω output impedance, the one-eighth rule says this source suits headphones of 8.0Ω and above. 15 of the 571 models here fall below that. Most of them are multi-driver in-ears, 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.
$109 · 125 mW into 32Ω · 0.4 Ω out
Compare →$109 · 125 mW into 32Ω · 1.0 Ω out
Compare →$109 · 80 mW into 32Ω · output Ω not published
Compare →$90 · 60 mW into 32Ω · 0.5 Ω out
Compare →$59 · 100 mW into 32Ω · 0.6 Ω out
Compare →$50 · 138 mW into 32Ω · output Ω not published
Compare →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.