The AKG K612 Pro is 120Ω at 91.8 dB/mW; the Dan Clark Audio Expanse is 26Ω at 90.0 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 Dan Clark Audio Expanse needs 1.8 dB more than the AKG K612 Pro to reach the same loudness — 10 mW against 6.6 mW.
| Specification | AKG K612 Pro | Dan Clark Audio Expanse |
|---|---|---|
| Impedance | 120 Ω | 26 Ω |
| Sensitivity | 91.8 dB/mW | 90.0 dB/mW |
| Sensitivity (voltage) | 101.0 dB/V | 105.9 dB/V |
| Power for 100 dB | 6.6 mW | 10 mW |
| Voltage for 100 dB | 0.89 V | 0.51 V |
| Current for 100 dB | 7.4 mA | 19.6 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 15.00 Ω | 3.25 Ω |
| Sources that reach 100 dB out of 280 | 277 | 279 |
2 of the 280 sources have the power for the Dan Clark Audio Expanse but not for the AKG K612 Pro — Apple USB-C dongle (EU), 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 Dan Clark Audio Expanse (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 Dan Clark Audio Expanse. Every figure on this page comes from what AKG and Dan Clark Audio published, or is derived from it — what AKG publishes and what Dan Clark Audio publishes, both counted.