The Beyerdynamic DT 1990 Pro (250Ω) is 250Ω at 102.0 dB/mW; the Sony MDR-7506 is 63Ω at 106.0 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 Beyerdynamic DT 1990 Pro (250Ω) needs 4.0 dB more than the Sony MDR-7506 to reach the same loudness — 0.63 mW against 0.25 mW.
| Specification | Beyerdynamic DT 1990 Pro (250Ω) | Sony MDR-7506 |
|---|---|---|
| Impedance | 250 Ω | 63 Ω |
| Sensitivity | 102.0 dB/mW | 106.0 dB/mW |
| Sensitivity (voltage) | 108.0 dB/V | 118.0 dB/V |
| Power for 100 dB | 0.63 mW | 0.25 mW |
| Voltage for 100 dB | 0.40 V | 0.13 V |
| Current for 100 dB | 1.6 mA | 2.0 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 31.25 Ω | 7.88 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.
18 sources are low enough in output impedance for the Beyerdynamic DT 1990 Pro (250Ω) under the one-eighth rule but not for the Sony MDR-7506 (Zoom AMS-22, Arturia MiniFuse 2, Arturia MiniFuse 1, 15 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: Beyerdynamic DT 1990 Pro (250Ω) and Sony MDR-7506. Every figure on this page comes from what Beyerdynamic and Sony published, or is derived from it — what Beyerdynamic publishes and what Sony publishes, both counted.