The Abyss AB-1266 Phi TC is 50Ω at 88.0 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 Abyss AB-1266 Phi TC needs 8.0 dB more than the Beyerdynamic DT 990 Pro (250Ω) to reach the same loudness — 16 mW against 2.5 mW.
| Specification | Abyss AB-1266 Phi TC | Beyerdynamic DT 990 Pro (250Ω) |
|---|---|---|
| Impedance | 50 Ω | 250 Ω |
| Sensitivity | 88.0 dB/mW | 96.0 dB |
| Sensitivity (voltage) | 101.0 dB/V | 102.0 dB/V |
| Power for 100 dB | 16 mW | 2.5 mW |
| Voltage for 100 dB | 0.89 V | 0.79 V |
| Current for 100 dB | 17.8 mA | 3.2 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 6.25 Ω | 31.25 Ω |
| Sources that reach 100 dB out of 280 | 275 | 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.
2 of the 280 sources have the power for the Beyerdynamic DT 990 Pro (250Ω) but not for the Abyss AB-1266 Phi TC — Zoom AMS-22, Tascam US-2x2HR.
18 sources are low enough in output impedance for the Beyerdynamic DT 990 Pro (250Ω) under the one-eighth rule but not for the Abyss AB-1266 Phi TC (Zoom AMS-22, Arturia MiniFuse 2, Arturia MiniFuse 1, 15 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.
The gap between these two in decibels does not change with volume — it is a property of the two headphones. What changes is the size of the numbers, and it changes fast: every 10 dB costs ten times the power. The row that matters is the one nearest the level you listen at, and for most people that is nearer the top of this table than the bottom.
The Abyss AB-1266 Phi TC is more demanding than 97% of the 567 non-electrostatic models in this database; the Beyerdynamic DT 990 Pro (250Ω) than 95%. Both figures use the same measure as the rest of the site: whichever runs out first against a 2 V, 100 mW dongle, voltage or power.
| dB SPL | Abyss AB-1266 Phi TC power | Abyss AB-1266 Phi TC voltage | Beyerdynamic DT 990 Pro (250Ω) power | Beyerdynamic DT 990 Pro (250Ω) voltage |
|---|---|---|---|---|
| 80 | 0.16 mW | 89 mV | 0.03 mW | 79 mV |
| 85 | 0.50 mW | 0.16 V | 0.08 mW | 0.14 V |
| 90 | 1.6 mW | 0.28 V | 0.25 mW | 0.25 V |
| 95 | 5.0 mW | 0.50 V | 0.79 mW | 0.45 V |
| 100 | 16 mW | 0.89 V | 2.5 mW | 0.79 V |
| 105 | 50 mW | 1.58 V | 7.9 mW | 1.41 V |
105 dB is included because forum power figures are usually quoted there or higher. It is also a level that damages hearing in minutes — how many minutes is its own calculator.
| Source | Price | Headroom, Abyss AB-1266 Phi TC | Headroom, Beyerdynamic DT 990 Pro (250Ω) | Output impedance | Noise |
|---|---|---|---|---|---|
| JadeAudio JA11 | $20 | 0.8 dB | 1.8 dB | 0.5 Ω | 1.7 µV |
| FiiO KA11 | $29 | 9.1 dB | 10.2 dB | 0.7 Ω | 1.7 µV |
| FiiO BTR11 | $36 | 0.8 dB | 1.6 dB | 0.5 Ω | 8.0 µV |
Of the 280 sources here, 275 reach 100 dB on both. That is the easy axis. 70 of them also publish an output impedance low enough for both under the one-eighth rule and a noise figure that stays below the audible-hiss threshold with both — the rest either fail one of those or never printed the number at all, and 203 of them are in the second group.
The cheapest of the 70 is the JadeAudio JA11, at $20. It leaves 0.8 dB of headroom on the Abyss AB-1266 Phi TC and 1.8 dB on the Beyerdynamic DT 990 Pro (250Ω), its output impedance is 0.5 Ω against a one-eighth limit of 6.25 Ω and 31.25 Ω, and its noise figure puts the hiss floor 34 dB and 33 dB below the 20 dB SPL this site treats as the point where a quiet room stops hiding it.
Cheapest that satisfies three published numbers is not the same as best, and none of it is about how either headphone sounds. To put either model against a source this page does not mention, or to change the target loudness, use the amplifier matcher.
| Model | As printed | Tolerance | Standard |
|---|---|---|---|
| Abyss AB-1266 Phi TC | 5 Hz - 45 KHz | not printed | not printed |
| Beyerdynamic DT 990 Pro (250Ω) | 5 - 35.000 Hz | not printed | not printed |
Abyss prints 5 Hz - 45 KHz for the AB-1266 Phi TC. Beyerdynamic prints 5 - 35.000 Hz for the DT 990 Pro (250Ω).
Neither range has a tolerance printed beside it, and that is the whole of what this section can tell you. A wider range on one sheet is not deeper bass or more treble on that headphone: without a tolerance, neither number says how loud either model is at the ends of its own range, so the difference between the two is a difference between two pieces of marketing copy. A ±dB figure is what turns a range into a specification, and of the 490 models whose maker prints a range, 58 print it.
None of this is a measurement. What each maker publishes, and what it is worth, is set out in the frequency response audit.
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 990 Pro (250Ω). Each figure on this page is labelled on those pages with where it came from, including the ones Abyss and Beyerdynamic never published — what Abyss publishes and what Beyerdynamic publishes, both counted.