The Meze Empyrean is 32Ω at 100.0 dB (no figure from the maker at all); the Sennheiser HD 650 is 300Ω at 97.8 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 650 needs 2.2 dB more than the Meze Empyrean to reach the same loudness — 1.7 mW against 1.0 mW.
| Specification | Meze Empyrean | Sennheiser HD 650 |
|---|---|---|
| Impedance | 32 Ω | 300 Ω |
| Sensitivity | 100.0 dB | 97.8 dB/mW |
| Sensitivity (voltage) | 114.9 dB/V | 103.0 dB/V |
| Power for 100 dB | 1.0 mW | 1.7 mW |
| Voltage for 100 dB | 0.18 V | 0.71 V |
| Current for 100 dB | 5.6 mA | 2.4 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 4.00 Ω | 37.50 Ω |
| Sources that reach 100 dB out of 280 | 280 | 280 |
One caution before reading the rows. For Meze Empyrean the maker publishes no sensitivity figure at all. The number in the table was collected when this database was first built and has never been traced to a manufacturer document, so treat every row below it as an estimate rather than a specification.
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.
20 sources are low enough in output impedance for the Sennheiser HD 650 under the one-eighth rule but not for the Meze Empyrean (Zoom AMS-22, Arturia MiniFuse 2, Arturia MiniFuse 1, 17 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: Meze Empyrean and Sennheiser HD 650. Each figure on this page is labelled on those pages with where it came from, including the ones Meze and Sennheiser never published — what Meze publishes and what Sennheiser publishes, both counted.