The Kiwi Ears Halcyon is 29Ω at 109.0 dB/mW; the Kiwi Ears Orchestra II is 15Ω at 110.0 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 Halcyon needs 1.0 dB more than the Orchestra II to reach the same loudness — 0.13 mW against 0.10 mW.
| Specification | Halcyon | Orchestra II |
|---|---|---|
| Impedance | 29 Ω | 15 Ω |
| Sensitivity | 109.0 dB/mW | 110.0 dB/mW |
| Sensitivity (voltage) | 124.4 dB/V | 128.2 dB/V |
| Power for 100 dB | 0.13 mW | 0.10 mW |
| Voltage for 100 dB | 60 mV | 39 mV |
| Current for 100 dB | 2.1 mA | 2.6 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 3.62 Ω | 1.88 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 are low enough in output impedance for the Halcyon under the one-eighth rule but not for the Orchestra II (Astell&Kern HC3, RME Fireface UFX II, RME Fireface UFX III).
8 sources stay below the audible-hiss threshold with the Halcyon but cross it with the Orchestra II (Grace Design m900, FiiO M33 R2R, FiiO K17, 5 more).
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: Kiwi Ears Halcyon and Kiwi Ears Orchestra II. Every figure on this page comes from what Kiwi Ears published, or is derived from it — what that maker publishes, counted.