The AKG K612 Pro is 120Ω at 91.8 dB/mW; the HiFiMAN HE400se is 25Ω at 91.0 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 HiFiMAN HE400se needs 0.8 dB more than the AKG K612 Pro to reach the same loudness — 7.9 mW against 6.6 mW.
| Specification | AKG K612 Pro | HiFiMAN HE400se |
|---|---|---|
| Impedance | 120 Ω | 25 Ω |
| Sensitivity | 91.8 dB/mW | 91.0 dB |
| Sensitivity (voltage) | 101.0 dB/V | 107.0 dB/V |
| Power for 100 dB | 6.6 mW | 7.9 mW |
| Voltage for 100 dB | 0.89 V | 0.45 V |
| Current for 100 dB | 7.4 mA | 17.8 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 15.00 Ω | 3.12 Ω |
| Sources that reach 100 dB out of 280 | 277 | 280 |
One caution before reading the rows. HiFiMAN HE400se 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.
3 of the 280 sources have the power for the HiFiMAN HE400se but not for the AKG K612 Pro — Apple USB-C dongle (EU), Steinberg UR22C, Sony NW-A306.
18 sources are low enough in output impedance for the AKG K612 Pro under the one-eighth rule but not for the HiFiMAN HE400se (Zoom AMS-22, Arturia MiniFuse 2, Arturia MiniFuse 1, 15 more).
277 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: AKG K612 Pro and HiFiMAN HE400se. Each figure on this page is labelled on those pages with where it came from, including the ones AKG and HiFiMAN never published — what AKG publishes and what HiFiMAN publishes, both counted.