The Sennheiser HD 569 is 23Ω at 98.6 dB/mW; the Sennheiser HD 599 is 50Ω at 93.0 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 HD 599 needs 5.6 dB more than the HD 569 to reach the same loudness — 5.0 mW against 1.4 mW.
| Specification | HD 569 | HD 599 |
|---|---|---|
| Impedance | 23 Ω | 50 Ω |
| Sensitivity | 98.6 dB/mW | 93.0 dB/mW |
| Sensitivity (voltage) | 115.0 dB/V | 106.0 dB/V |
| Power for 100 dB | 1.4 mW | 5.0 mW |
| Voltage for 100 dB | 0.18 V | 0.50 V |
| Current for 100 dB | 7.7 mA | 10.0 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 2.88 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 HD 599 under the one-eighth rule but not for the HD 569 (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: Sennheiser HD 569 and Sennheiser HD 599. Every figure on this page comes from what Sennheiser published, or is derived from it — what that maker publishes, counted.