The Meze 109 Pro is 40Ω at 112.0 dB/mW; the Sennheiser HD 800S is 300Ω at 96.8 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 Sennheiser HD 800S needs 15.2 dB more than the Meze 109 Pro to reach the same loudness — 2.1 mW against 0.06 mW.
| Specification | Meze 109 Pro | Sennheiser HD 800S |
|---|---|---|
| Impedance | 40 Ω | 300 Ω |
| Sensitivity | 112.0 dB/mW | 96.8 dB/mW |
| Sensitivity (voltage) | 126.0 dB/V | 102.0 dB/V |
| Power for 100 dB | 0.06 mW | 2.1 mW |
| Voltage for 100 dB | 50 mV | 0.79 V |
| Current for 100 dB | 1.3 mA | 2.6 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 5.00 Ω | 37.50 Ω |
| Sources that reach 100 dB out of 280 | 280 | 277 |
3 of the 280 sources have the power for the Meze 109 Pro but not for the Sennheiser HD 800S — Apple USB-C dongle (EU), Steinberg UR22C, Sony NW-A306.
19 sources are low enough in output impedance for the Sennheiser HD 800S under the one-eighth rule but not for the Meze 109 Pro (Zoom AMS-22, Arturia MiniFuse 2, Arturia MiniFuse 1, 16 more).
13 sources stay below the audible-hiss threshold with the Sennheiser HD 800S but cross it with the Meze 109 Pro (FiiO BTR11, FiiO K11 R2R, Lake People G103-S Mk II, 10 more).
277 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: Meze 109 Pro and Sennheiser HD 800S. Every figure on this page comes from what Meze and Sennheiser published, or is derived from it — what Meze publishes and what Sennheiser publishes, both counted.