Short answer
Both are Bluetooth receivers, $36 against $50.
The Fosi Audio N3 reaches 100 dB on 562 of the 567 models here, the FiiO BTR11 on 549.
| Specification | FiiO BTR11 | Fosi Audio N3 |
|---|---|---|
| Power into 32Ω | 30 mW | 138 mW |
| Power into 150Ω | 6.2 mW | 30 mW |
| Power into 300Ω | 3.0 mW | 15 mW |
| Power into 600Ω | 1.5 mW | 7.5 mW |
| Output impedance | 0.5 Ω | not published |
| Output noise | 8.0 µV | not published |
| Price | $36 | $50 |
| Headphones it reaches 100 dB on out of 567 | 549 | 562 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Load | FiiO BTR11 | Fosi Audio N3 |
|---|---|---|
| 32 Ω | Published | Published |
| 150 Ω | Derived | Derived |
| 300 Ω | Published | Published |
| 600 Ω | Derived | Derived |
Both makers publish a power rating. FiiO BTR11 publishes at 32 Ω and at 300 Ω; Fosi Audio N3 at 32 Ω and at 300 Ω. The other rows are worked out from those.
The two publish at the same loads, which is the one case where the rows of this table can be read straight across.
13 headphones reach 100 dB on the Fosi Audio N3 but not on the FiiO BTR11 — Audio-Technica ATH-R70xa, Beyerdynamic DT 880 Edition (600Ω), Beyerdynamic DT 990 Edition (600Ω), 10 more.
549 of the 567 models here reach 100 dB on both.
Headroom is at a 100 dB SPL peak.
The widest gap on the list is the Audio-Technica ATH-R70X: Fosi Audio N3 has +8 dB of headroom there against +1 dB. 7 dB is about 5 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Fosi Audio N3 because that maker publishes no output noise figure.
| Headphone | Impedance | Needs | FiiO BTR11 headroom | Fosi Audio N3 headroom | FiiO BTR11 hiss | Fosi Audio N3 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +28 dB | +30 dB | 33 dB | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +8 dB | +10 dB | 13 dB | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +12 dB | +19 dB | 11 dB | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +8 dB | +15 dB | 6 dB | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +6 dB | +11 dB | 5 dB | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +1 dB | +8 dB | -1 dB | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | -3 dB | +4 dB | -5 dB | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | -5 dB | +2 dB | -7 dB | not published |
The Fosi Audio N3 costs $14 more than the FiiO BTR11. Out of the 567 models here, that difference buys 13 more models driven to 100 dB.
Nothing runs the other way: there is no axis here on which the cheaper of the two does better.
Only published figures count here; blank axes are counted separately.
Each in full: FiiO BTR11 and Fosi Audio N3.