The Audio-Technica ATH-CKS1100 is 12Ω at 110.0 dB/mW; the Audio-Technica ATH-E40 is 12Ω at 107.0 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 ATH-E40 needs 3.0 dB more than the ATH-CKS1100 to reach the same loudness — 0.20 mW against 0.10 mW.
| Specification | ATH-CKS1100 | ATH-E40 |
|---|---|---|
| Impedance | 12 Ω | 12 Ω |
| Sensitivity | 110.0 dB/mW | 107.0 dB/mW |
| Sensitivity (voltage) | 129.2 dB/V | 126.2 dB/V |
| Power for 100 dB | 0.10 mW | 0.20 mW |
| Voltage for 100 dB | 35 mV | 49 mV |
| Current for 100 dB | 2.9 mA | 4.1 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 1.50 Ω | 1.50 Ω |
| Sources that reach 100 dB out of 280 | 280 | 280 |
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.
3 sources stay below the audible-hiss threshold with the ATH-E40 but cross it with the ATH-CKS1100 (FiiO K19, FiiO M17, FiiO M27).
280 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-CKS1100 and Audio-Technica ATH-E40. Every figure on this page comes from what Audio-Technica published, or is derived from it — what that maker publishes, counted.