The ZMF Caldera is 60Ω at 95.0 dB/mW; the ZMF Eikon is 300Ω at 98.0 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 3.0 dB more than the Eikon to reach the same loudness — 3.2 mW against 1.6 mW.
| Specification | Caldera | Eikon |
|---|---|---|
| Impedance | 60 Ω | 300 Ω |
| Sensitivity | 95.0 dB/mW | 98.0 dB/mW |
| Sensitivity (voltage) | 107.2 dB/V | 103.2 dB/V |
| Power for 100 dB | 3.2 mW | 1.6 mW |
| Voltage for 100 dB | 0.44 V | 0.69 V |
| Current for 100 dB | 7.3 mA | 2.3 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 | 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.
19 sources are low enough in output impedance for the Eikon under the one-eighth rule but not for the Caldera (Zoom AMS-22, Arturia MiniFuse 2, Arturia MiniFuse 1, 16 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.
The gap between these two in decibels does not change with volume — it is a property of the two headphones. What changes is the size of the numbers, and it changes fast: every 10 dB costs ten times the power. The row that matters is the one nearest the level you listen at, and for most people that is nearer the top of this table than the bottom.
The Eikon is more demanding than 93% of the 567 non-electrostatic models in this database; the Caldera than 84%. Both figures use the same measure as the rest of the site: whichever runs out first against a 2 V, 100 mW dongle, voltage or power.
| dB SPL | Caldera power | Caldera voltage | Eikon power | Eikon voltage |
|---|---|---|---|---|
| 80 | 0.03 mW | 44 mV | 0.02 mW | 69 mV |
| 85 | 0.10 mW | 77 mV | 0.05 mW | 0.12 V |
| 90 | 0.32 mW | 0.14 V | 0.16 mW | 0.22 V |
| 95 | 1.0 mW | 0.24 V | 0.50 mW | 0.39 V |
| 100 | 3.2 mW | 0.44 V | 1.6 mW | 0.69 V |
| 105 | 10 mW | 0.77 V | 5.0 mW | 1.23 V |
105 dB is included because forum power figures are usually quoted there or higher. It is also a level that damages hearing in minutes — how many minutes is its own calculator.
| Source | Price | Headroom, Caldera | Headroom, Eikon | Output impedance | Noise |
|---|---|---|---|---|---|
| JadeAudio JA11 | $20 | 7.0 dB | 3.1 dB | 0.5 Ω | 1.7 µV |
| FiiO KA11 | $29 | 15.3 dB | 11.4 dB | 0.7 Ω | 1.7 µV |
| FiiO BTR11 | $36 | 7.0 dB | 2.8 dB | 0.5 Ω | 8.0 µV |
Of the 280 sources here, 280 reach 100 dB on both. That is the easy axis. 70 of them also publish an output impedance low enough for both under the one-eighth rule and a noise figure that stays below the audible-hiss threshold with both — the rest either fail one of those or never printed the number at all, and 208 of them are in the second group.
The cheapest of the 70 is the JadeAudio JA11, at $20. It leaves 7.0 dB of headroom on the Caldera and 3.1 dB on the Eikon, its output impedance is 0.5 Ω against a one-eighth limit of 7.50 Ω and 37.50 Ω, and its noise figure puts the hiss floor 28 dB and 32 dB below the 20 dB SPL this site treats as the point where a quiet room stops hiding it.
Cheapest that satisfies three published numbers is not the same as best, and none of it is about how either headphone sounds. To put either model against a source this page does not mention, or to change the target loudness, use the amplifier matcher.
| Model | As printed | Tolerance | Standard |
|---|---|---|---|
| Caldera | nothing printed | — | — |
| Eikon | Approximately 10 Hz to 25 KHZ | not printed | not printed |
ZMF prints nothing at all for the Caldera and Approximately 10 Hz to 25 KHZ for the Eikon.
Eikon: ZMF prints one specification block for the Auteur and the Eikon together, and hedges the range with the word “Approximately” rather than a tolerance. It is the only range in this audit that qualifies itself in words instead of decibels. ZMF’s own shop pages for these models print no frequency row at all.
So one side of this comparison has a frequency-response number and the other does not — which changes less than it looks. The range printed for the Eikon comes with no tolerance beside it, and a range without a ±dB figure says nothing about how loud the headphone is at either end of it: thirty decibels down at the bottom and the sentence would still be true. On the only reading that would have made it a specification, the two sheets say the same amount: nothing.
None of this is a measurement. What each maker publishes, and what it is worth, is set out in the frequency response audit.
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 Eikon. Every figure on this page comes from what ZMF published, or is derived from it — what that maker publishes, counted.