The Beyerdynamic DT 1770 PRO MKII is 30Ω at 95.0 dB/mW; the Beyerdynamic DT 990 Edition (600Ω) is 600Ω 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 DT 1770 PRO MKII needs 1.0 dB more than the DT 990 Edition (600Ω) to reach the same loudness — 3.2 mW against 2.5 mW.
| Specification | DT 1770 PRO MKII | DT 990 Edition (600Ω) |
|---|---|---|
| Impedance | 30 Ω | 600 Ω |
| Sensitivity | 95.0 dB/mW | 96.0 dB |
| Sensitivity (voltage) | 110.2 dB/V | 98.2 dB/V |
| Power for 100 dB | 3.2 mW | 2.5 mW |
| Voltage for 100 dB | 0.31 V | 1.23 V |
| Current for 100 dB | 10.3 mA | 2.0 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 3.75 Ω | 75.00 Ω |
| Sources that reach 100 dB out of 280 | 280 | 266 |
One caution before reading the rows. Beyerdynamic DT 990 Edition (600Ω) 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.
14 of the 280 sources have the power for the DT 1770 PRO MKII but not for the DT 990 Edition (600Ω) — Apple USB-C dongle (US), Apple USB-C dongle (EU), JadeAudio JA11, 11 more.
34 sources are low enough in output impedance for the DT 990 Edition (600Ω) under the one-eighth rule but not for the DT 1770 PRO MKII (Zoom AMS-22, Audient EVO 4, ART HeadAmp 4 Pro, 31 more).
266 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 1770 PRO MKII and Beyerdynamic DT 990 Edition (600Ω). Each figure on this page is labelled on those pages with where it came from, including the ones Beyerdynamic never published — what that maker publishes, counted.