The Abyss AB-1266 Phi TC is 50Ω at 88.0 dB/mW; the Beyerdynamic DT 900 Pro X is 48Ω at 100.0 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 Abyss AB-1266 Phi TC needs 12.0 dB more than the Beyerdynamic DT 900 Pro X to reach the same loudness — 16 mW against 1.0 mW.
| Specification | Abyss AB-1266 Phi TC | Beyerdynamic DT 900 Pro X |
|---|---|---|
| Impedance | 50 Ω | 48 Ω |
| Sensitivity | 88.0 dB/mW | 100.0 dB/mW |
| Sensitivity (voltage) | 101.0 dB/V | 113.2 dB/V |
| Power for 100 dB | 16 mW | 1.0 mW |
| Voltage for 100 dB | 0.89 V | 0.22 V |
| Current for 100 dB | 17.8 mA | 4.6 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 6.25 Ω | 6.00 Ω |
| Sources that reach 100 dB out of 280 | 275 | 280 |
5 of the 280 sources have the power for the Beyerdynamic DT 900 Pro X but not for the Abyss AB-1266 Phi TC — Apple USB-C dongle (EU), Zoom AMS-22, Steinberg UR22C, 2 more.
275 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: Abyss AB-1266 Phi TC and Beyerdynamic DT 900 Pro X. Every figure on this page comes from what Abyss and Beyerdynamic published, or is derived from it — what Abyss publishes and what Beyerdynamic publishes, both counted.