The Final Audio A4000 is 18Ω at 100.0 dB/mW; the Final Audio E5000 is 14Ω at 93.0 dB (no reference unit printed). This page is only about what they ask of an amplifier — not how they sound, which no specification on either sheet can tell you.
The E5000 needs 7.0 dB more than the A4000 to reach the same loudness — 5.0 mW against 1.0 mW.
| Specification | A4000 | E5000 |
|---|---|---|
| Impedance | 18 Ω | 14 Ω |
| Sensitivity | 100.0 dB/mW | 93.0 dB |
| Sensitivity (voltage) | 117.4 dB/V | 111.5 dB/V |
| Power for 100 dB | 1.0 mW | 5.0 mW |
| Voltage for 100 dB | 0.13 V | 0.26 V |
| Current for 100 dB | 7.5 mA | 18.9 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 2.25 Ω | 1.75 Ω |
| Sources that reach 100 dB out of 280 | 280 | 280 |
One caution before reading the rows. Final Audio E5000 printed a decibel figure with no reference unit, so this page reads it as per milliwatt. If it is really per volt, that model needs far more than the table says. Why the two readings differ by so much.
Every source in the database that drives one of them drives the other. On power, the choice between these two changes nothing about what amplifier you need.
4 sources are low enough in output impedance for the A4000 under the one-eighth rule but not for the E5000 (Schiit Vali 2+, Astell&Kern HC3, RME Fireface UFX II, 1 more).
280 of the 280 sources here reach 100 dB on both. That count is about power only — the output-impedance and hiss lines above are separate questions, and a source can pass this one and fail those.
Each model has a page of its own with the full source list, the hiss estimate and the provenance of every figure above: Final Audio A4000 and Final Audio E5000. Each figure on this page is labelled on those pages with where it came from, including the ones Final Audio never published — what that maker publishes, counted.