The AKG K612 Pro is 120Ω at 91.8 dB/mW; the Audeze LCD-2 Classic is 70Ω at 101.0 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 9.2 dB more than the Audeze LCD-2 Classic to reach the same loudness — 6.6 mW against 0.79 mW.
| Specification | AKG K612 Pro | Audeze LCD-2 Classic |
|---|---|---|
| Impedance | 120 Ω | 70 Ω |
| Sensitivity | 91.8 dB/mW | 101.0 dB/mW |
| Sensitivity (voltage) | 101.0 dB/V | 112.5 dB/V |
| Power for 100 dB | 6.6 mW | 0.79 mW |
| Voltage for 100 dB | 0.89 V | 0.24 V |
| Current for 100 dB | 7.4 mA | 3.4 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 15.00 Ω | 8.75 Ω |
| Sources that reach 100 dB out of 280 | 277 | 280 |
3 of the 280 sources have the power for the Audeze LCD-2 Classic but not for the AKG K612 Pro — Apple USB-C dongle (EU), Steinberg UR22C, Sony NW-A306.
17 sources are low enough in output impedance for the AKG K612 Pro under the one-eighth rule but not for the Audeze LCD-2 Classic (Zoom AMS-22, Arturia MiniFuse 2, Arturia MiniFuse 1, 14 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 Audeze LCD-2 Classic. Every figure on this page comes from what AKG and Audeze published, or is derived from it — what AKG publishes and what Audeze publishes, both counted.