The Moondrop COSMO is 15Ω at 81.8 dB/mW; the Moondrop Old Fashioned is 32Ω at 94.1 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 COSMO needs 12.3 dB more than the Old Fashioned to reach the same loudness — 66 mW against 3.9 mW.
| Specification | COSMO | Old Fashioned |
|---|---|---|
| Impedance | 15 Ω | 32 Ω |
| Sensitivity | 81.8 dB/mW | 94.1 dB/mW |
| Sensitivity (voltage) | 100.0 dB/V | 109.0 dB/V |
| Power for 100 dB | 66 mW | 3.9 mW |
| Voltage for 100 dB | 1.00 V | 0.35 V |
| Current for 100 dB | 66.4 mA | 11.0 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 1.88 Ω | 4.00 Ω |
| Sources that reach 100 dB out of 280 | 188 | 280 |
92 of the 280 sources have the power for the Old Fashioned but not for the COSMO — Apple USB-C dongle (US), Apple USB-C dongle (EU), Generic CX31993 dongles, 89 more.
3 sources are low enough in output impedance for the Old Fashioned under the one-eighth rule but not for the COSMO (Astell&Kern HC3, RME Fireface UFX II, RME Fireface UFX III).
188 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 COSMO is more demanding than 99% of the 567 non-electrostatic models in this database; the Old Fashioned than 79%. 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 | COSMO power | COSMO voltage | Old Fashioned power | Old Fashioned voltage |
|---|---|---|---|---|
| 80 | 0.66 mW | 100 mV | 0.04 mW | 35 mV |
| 85 | 2.1 mW | 0.18 V | 0.12 mW | 63 mV |
| 90 | 6.6 mW | 0.31 V | 0.39 mW | 0.11 V |
| 95 | 21 mW | 0.56 V | 1.2 mW | 0.20 V |
| 100 | 66 mW | 1.00 V | 3.9 mW | 0.35 V |
| 105 | 209 mW | 1.77 V | 12 mW | 0.63 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, COSMO | Headroom, Old Fashioned | Output impedance | Noise |
|---|---|---|---|---|---|
| FiiO KA11 | $29 | 5.4 dB | 17.1 dB | 0.7 Ω | 1.7 µV |
| FiiO BTR13 | $59 | 2.3 dB | 14.1 dB | 0.6 Ω | 1.0 µV |
| FiiO KA3 | $79 | 2.3 dB | 15.2 dB | 0.5 Ω | 1.7 µV |
Of the 280 sources here, 188 reach 100 dB on both. That is the easy axis. 66 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 120 of them are in the second group.
The cheapest of the 66 is the FiiO KA11, at $29. It leaves 5.4 dB of headroom on the COSMO and 17.1 dB on the Old Fashioned, its output impedance is 0.7 Ω against a one-eighth limit of 1.88 Ω and 4.00 Ω, and its noise figure puts the hiss floor 35 dB and 26 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 |
|---|---|---|---|
| COSMO | 13Hz- 58kHz (IEC61094, Free Field) | not printed | IEC61094 (free field) |
| 20Hz- 20kHz (IEC60318-4, -3dB) | -3 dB | IEC60318-4 | |
| Old Fashioned | 20Hz - 32kHz (IEC61094, Free Field) | not printed | IEC61094 (free field) |
| 20Hz - 20kHz (IEC60318-4, -3dB) | -3 dB | IEC60318-4 |
Moondrop prints two ranges, “13Hz- 58kHz (IEC61094, Free Field)” and “20Hz- 20kHz (IEC60318-4, -3dB)”, for the COSMO and two ranges, “20Hz - 32kHz (IEC61094, Free Field)” and “20Hz - 20kHz (IEC60318-4, -3dB)”, for the Old Fashioned.
Both sheets print a tolerance, which is rare enough to be worth pointing at: only 58 of the 490 models with a printed range do. These two ranges can be set against each other, because each of them says how far down the response is allowed to be at the ends.
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: Moondrop COSMO and Moondrop Old Fashioned. Every figure on this page comes from what Moondrop published, or is derived from it — what that maker publishes, counted.