The Moondrop Chu II is 18Ω at 101.6 dB/mW; the Moondrop S8 is 16Ω at 104.0 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 Chu II needs 2.4 dB more than the S8 to reach the same loudness — 0.69 mW against 0.40 mW.
| Specification | Chu II | S8 |
|---|---|---|
| Impedance | 18 Ω | 16 Ω |
| Sensitivity | 101.6 dB/mW | 104.0 dB/mW |
| Sensitivity (voltage) | 119.0 dB/V | 122.0 dB/V |
| Power for 100 dB | 0.69 mW | 0.40 mW |
| Voltage for 100 dB | 0.11 V | 80 mV |
| Current for 100 dB | 6.2 mA | 5.0 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 2.25 Ω | 2.00 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.
2 sources stay below the audible-hiss threshold with the Chu II but cross it with the S8 (FiiO BTR11, Rupert Neve RNHP).
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: Moondrop Chu II and Moondrop S8. Every figure on this page comes from what Moondrop published, or is derived from it — what that maker publishes, counted.