The 64 Audio U12t is 12.6Ω at 108.0 dB/mW; the Letshuoer S12 Pro is 16Ω at 102.0 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 Letshuoer S12 Pro needs 6.0 dB more than the 64 Audio U12t to reach the same loudness — 0.63 mW against 0.16 mW.
| Specification | 64 Audio U12t | Letshuoer S12 Pro |
|---|---|---|
| Impedance | 12.6 Ω | 16 Ω |
| Sensitivity | 108.0 dB/mW | 102.0 dB/mW |
| Sensitivity (voltage) | 127.0 dB/V | 120.0 dB/V |
| Power for 100 dB | 0.16 mW | 0.63 mW |
| Voltage for 100 dB | 45 mV | 0.10 V |
| Current for 100 dB | 3.5 mA | 6.3 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 1.57 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 Letshuoer S12 Pro under the one-eighth rule but not for the 64 Audio U12t (FiiO KA13, Schiit Vali 2+, Astell&Kern HC3, 2 more).
15 sources stay below the audible-hiss threshold with the Letshuoer S12 Pro but cross it with the 64 Audio U12t (FiiO BTR11, FiiO K11 R2R, Lake People G103-S Mk II, 12 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: 64 Audio U12t and Letshuoer S12 Pro. Every figure on this page comes from what 64 Audio and Letshuoer published, or is derived from it — what 64 Audio publishes and what Letshuoer publishes, both counted.