The Audeze MM-500 is 18Ω at 100.0 dB/mW; the Beyerdynamic DT 990 Pro (250Ω) is 250Ω at 96.0 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.
The Beyerdynamic DT 990 Pro (250Ω) needs 4.0 dB more than the Audeze MM-500 to reach the same loudness — 2.5 mW against 1.0 mW.
| Specification | Audeze MM-500 | Beyerdynamic DT 990 Pro (250Ω) |
|---|---|---|
| Impedance | 18 Ω | 250 Ω |
| Sensitivity | 100.0 dB/mW | 96.0 dB |
| Sensitivity (voltage) | 117.4 dB/V | 102.0 dB/V |
| Power for 100 dB | 1.0 mW | 2.5 mW |
| Voltage for 100 dB | 0.13 V | 0.79 V |
| Current for 100 dB | 7.5 mA | 3.2 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 2.25 Ω | 31.25 Ω |
| Sources that reach 100 dB out of 280 | 280 | 277 |
One caution before reading the rows. Beyerdynamic DT 990 Pro (250Ω) 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.
3 of the 280 sources have the power for the Audeze MM-500 but not for the Beyerdynamic DT 990 Pro (250Ω) — Apple USB-C dongle (EU), Steinberg UR22C, Sony NW-A306.
19 sources are low enough in output impedance for the Beyerdynamic DT 990 Pro (250Ω) under the one-eighth rule but not for the Audeze MM-500 (Zoom AMS-22, Arturia MiniFuse 2, Arturia MiniFuse 1, 16 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: Audeze MM-500 and Beyerdynamic DT 990 Pro (250Ω). Each figure on this page is labelled on those pages with where it came from, including the ones Audeze and Beyerdynamic never published — what Audeze publishes and what Beyerdynamic publishes, both counted.