The Fostex T50RP MK3 is 50Ω at 92.0 dB/mW; the Meze 109 Pro is 40Ω at 112.0 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 Fostex T50RP MK3 needs 20.0 dB more than the Meze 109 Pro to reach the same loudness — 6.3 mW against 0.06 mW.
| Specification | Fostex T50RP MK3 | Meze 109 Pro |
|---|---|---|
| Impedance | 50 Ω | 40 Ω |
| Sensitivity | 92.0 dB/mW | 112.0 dB/mW |
| Sensitivity (voltage) | 105.0 dB/V | 126.0 dB/V |
| Power for 100 dB | 6.3 mW | 0.06 mW |
| Voltage for 100 dB | 0.56 V | 50 mV |
| Current for 100 dB | 11.2 mA | 1.3 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 6.25 Ω | 5.00 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.
13 sources stay below the audible-hiss threshold with the Fostex T50RP MK3 but cross it with the Meze 109 Pro (FiiO BTR11, FiiO K11 R2R, Lake People G103-S Mk II, 10 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: Fostex T50RP MK3 and Meze 109 Pro. Every figure on this page comes from what Fostex and Meze published, or is derived from it — what Fostex publishes and what Meze publishes, both counted.