The AKG K702 is 62Ω at 92.9 dB/mW; the Beyerdynamic DT 1990 Pro (250Ω) is 250Ω at 102.0 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 AKG K702 needs 9.1 dB more than the Beyerdynamic DT 1990 Pro (250Ω) to reach the same loudness — 5.1 mW against 0.63 mW.
| Specification | AKG K702 | Beyerdynamic DT 1990 Pro (250Ω) |
|---|---|---|
| Impedance | 62 Ω | 250 Ω |
| Sensitivity | 92.9 dB/mW | 102.0 dB/mW |
| Sensitivity (voltage) | 105.0 dB/V | 108.0 dB/V |
| Power for 100 dB | 5.1 mW | 0.63 mW |
| Voltage for 100 dB | 0.56 V | 0.40 V |
| Current for 100 dB | 9.1 mA | 1.6 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 7.75 Ω | 31.25 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.
18 sources are low enough in output impedance for the Beyerdynamic DT 1990 Pro (250Ω) under the one-eighth rule but not for the AKG K702 (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: AKG K702 and Beyerdynamic DT 1990 Pro (250Ω). Every figure on this page comes from what AKG and Beyerdynamic published, or is derived from it — what AKG publishes and what Beyerdynamic publishes, both counted.