The Sennheiser HD 280 Pro is 64Ω at 113.0 dB (no reference unit printed); the Sennheiser HD 600 is 300Ω at 91.8 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 HD 600 needs 21.2 dB more than the HD 280 Pro to reach the same loudness — 6.6 mW against 0.05 mW.
| Specification | HD 280 Pro | HD 600 |
|---|---|---|
| Impedance | 64 Ω | 300 Ω |
| Sensitivity | 113.0 dB | 91.8 dB/mW |
| Sensitivity (voltage) | 124.9 dB/V | 97.0 dB/V |
| Power for 100 dB | 0.05 mW | 6.6 mW |
| Voltage for 100 dB | 57 mV | 1.41 V |
| Current for 100 dB | 0.9 mA | 4.7 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 8.00 Ω | 37.50 Ω |
| Sources that reach 100 dB out of 280 | 280 | 261 |
One caution before reading the rows. Sennheiser HD 280 Pro 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.
19 of the 280 sources have the power for the HD 280 Pro but not for the HD 600 — Apple USB-C dongle (US), Apple USB-C dongle (EU), JadeAudio JA11, 16 more.
19 sources are low enough in output impedance for the HD 600 under the one-eighth rule but not for the HD 280 Pro (Zoom AMS-22, Arturia MiniFuse 2, Arturia MiniFuse 1, 16 more).
8 sources stay below the audible-hiss threshold with the HD 600 but cross it with the HD 280 Pro (FiiO BTR11, FiiO K11 R2R, Lake People G103-S Mk II, 5 more).
261 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: Sennheiser HD 280 Pro and Sennheiser HD 600. Each figure on this page is labelled on those pages with where it came from, including the ones Sennheiser never published — what that maker publishes, counted.