The AKG K612 Pro is 120Ω at 91.8 dB/mW; the ZMF Atrium is 300Ω at 96.0 dB/mW. 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 AKG K612 Pro needs 4.2 dB more than the ZMF Atrium to reach the same loudness — 6.6 mW against 2.5 mW.
| Specification | AKG K612 Pro | ZMF Atrium |
|---|---|---|
| Impedance | 120 Ω | 300 Ω |
| Sensitivity | 91.8 dB/mW | 96.0 dB/mW |
| Sensitivity (voltage) | 101.0 dB/V | 101.2 dB/V |
| Power for 100 dB | 6.6 mW | 2.5 mW |
| Voltage for 100 dB | 0.89 V | 0.87 V |
| Current for 100 dB | 7.4 mA | 2.9 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 15.00 Ω | 37.50 Ω |
| Sources that reach 100 dB out of 280 | 277 | 277 |
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.
2 sources are low enough in output impedance for the ZMF Atrium under the one-eighth rule but not for the AKG K612 Pro (Schiit Valhalla 3, Arturia AudioFuse Rev2).
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 ZMF Atrium. Every figure on this page comes from what AKG and ZMF published, or is derived from it — what AKG publishes and what ZMF publishes, both counted.