The ZMF Caldera is 60Ω at 95.0 dB/mW; the ZMF Verite Open is 300Ω at 97.0 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 Caldera needs 2.0 dB more than the Verite Open to reach the same loudness — 3.2 mW against 2.0 mW.
| Specification | Caldera | Verite Open |
|---|---|---|
| Impedance | 60 Ω | 300 Ω |
| Sensitivity | 95.0 dB/mW | 97.0 dB/mW |
| Sensitivity (voltage) | 107.2 dB/V | 102.2 dB/V |
| Power for 100 dB | 3.2 mW | 2.0 mW |
| Voltage for 100 dB | 0.44 V | 0.77 V |
| Current for 100 dB | 7.3 mA | 2.6 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 7.50 Ω | 37.50 Ω |
| Sources that reach 100 dB out of 280 | 280 | 279 |
1 of the 280 sources has the power for the Caldera but not for the Verite Open — Sony NW-A306.
19 sources are low enough in output impedance for the Verite Open under the one-eighth rule but not for the Caldera (Zoom AMS-22, Arturia MiniFuse 2, Arturia MiniFuse 1, 16 more).
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: ZMF Caldera and ZMF Verite Open. Every figure on this page comes from what ZMF published, or is derived from it — what that maker publishes, counted.