The Audio-Technica ATH-M40X is 35Ω at 98.0 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 8.0 dB more than the Audio-Technica ATH-M40X to reach the same loudness — 10 mW against 1.6 mW.
| Specification | Audio-Technica ATH-M40X | Dan Clark Audio Expanse |
|---|---|---|
| Impedance | 35 Ω | 26 Ω |
| Sensitivity | 98.0 dB/mW | 90.0 dB/mW |
| Sensitivity (voltage) | 112.6 dB/V | 105.9 dB/V |
| Power for 100 dB | 1.6 mW | 10 mW |
| Voltage for 100 dB | 0.24 V | 0.51 V |
| Current for 100 dB | 6.7 mA | 19.6 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 4.38 Ω | 3.25 Ω |
| Sources that reach 100 dB out of 280 | 280 | 279 |
1 of the 280 sources has the power for the Audio-Technica ATH-M40X but not for the Dan Clark Audio Expanse — Steinberg UR22C.
279 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: Audio-Technica ATH-M40X and Dan Clark Audio Expanse. Every figure on this page comes from what Audio-Technica and Dan Clark Audio published, or is derived from it — what Audio-Technica publishes and what Dan Clark Audio publishes, both counted.