The Fostex T50RPmk4Q is 28Ω at 97.0 dB/mW; the Fostex T60RP is 50Ω at 92.0 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 T60RP needs 5.0 dB more than the T50RPmk4Q to reach the same loudness — 6.3 mW against 2.0 mW.
| Specification | T50RPmk4Q | T60RP |
|---|---|---|
| Impedance | 28 Ω | 50 Ω |
| Sensitivity | 97.0 dB/mW | 92.0 dB/mW |
| Sensitivity (voltage) | 112.5 dB/V | 105.0 dB/V |
| Power for 100 dB | 2.0 mW | 6.3 mW |
| Voltage for 100 dB | 0.24 V | 0.56 V |
| Current for 100 dB | 8.4 mA | 11.2 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 3.50 Ω | 6.25 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.
1 source is low enough in output impedance for the T60RP under the one-eighth rule but not for the T50RPmk4Q (Shanling H5).
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 T50RPmk4Q and Fostex T60RP. Every figure on this page comes from what Fostex published, or is derived from it — what that maker publishes, counted.