The Fostex T50RP MK3 is 50Ω at 92.0 dB/mW; the HiFiMAN Sundara is 32Ω at 92.0 dB (no reference unit printed). This page is only about what they ask of an amplifier — not how they sound, which no specification on either sheet can tell you.
In amplifier terms these two are the same headphone. The gap between what they need for 100 dB is under half a decibel, which is smaller than the step between two clicks of most volume controls.
| Specification | Fostex T50RP MK3 | HiFiMAN Sundara |
|---|---|---|
| Impedance | 50 Ω | 32 Ω |
| Sensitivity | 92.0 dB/mW | 92.0 dB |
| Sensitivity (voltage) | 105.0 dB/V | 106.9 dB/V |
| Power for 100 dB | 6.3 mW | 6.3 mW |
| Voltage for 100 dB | 0.56 V | 0.45 V |
| Current for 100 dB | 11.2 mA | 14.0 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 6.25 Ω | 4.00 Ω |
| Sources that reach 100 dB out of 280 | 280 | 280 |
One caution before reading the rows. HiFiMAN Sundara printed a decibel figure with no reference unit, so this page reads it as per milliwatt. If it is really per volt, that model needs far more than the table says. Why the two readings differ by so much.
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 Fostex T50RP MK3 under the one-eighth rule but not for the HiFiMAN Sundara (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 T50RP MK3 and HiFiMAN Sundara. Each figure on this page is labelled on those pages with where it came from, including the ones Fostex and HiFiMAN never published — what Fostex publishes and what HiFiMAN publishes, both counted.