The Softears Studio4 is 12Ω at 103.8 dB/mW; the Softears Twilight is 16Ω at 105.0 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 Studio4 needs 1.2 dB more than the Twilight to reach the same loudness — 0.42 mW against 0.32 mW.
| Specification | Studio4 | Twilight |
|---|---|---|
| Impedance | 12 Ω | 16 Ω |
| Sensitivity | 103.8 dB/mW | 105.0 dB/mW |
| Sensitivity (voltage) | 123.0 dB/V | 123.0 dB/V |
| Power for 100 dB | 0.42 mW | 0.32 mW |
| Voltage for 100 dB | 71 mV | 71 mV |
| Current for 100 dB | 5.9 mA | 4.4 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 1.50 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.
5 sources are low enough in output impedance for the Twilight under the one-eighth rule but not for the Studio4 (FiiO KA13, Schiit Vali 2+, Astell&Kern HC3, 2 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: Softears Studio4 and Softears Twilight. Every figure on this page comes from what Softears published, or is derived from it — what that maker publishes, counted.