The AKG K612 Pro is 120Ω at 91.8 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 AKG K612 Pro needs 8.2 dB more than the Beyerdynamic DT 900 Pro X to reach the same loudness — 6.6 mW against 1.0 mW.
| Specification | AKG K612 Pro | Beyerdynamic DT 900 Pro X |
|---|---|---|
| Impedance | 120 Ω | 48 Ω |
| Sensitivity | 91.8 dB/mW | 100.0 dB/mW |
| Sensitivity (voltage) | 101.0 dB/V | 113.2 dB/V |
| Power for 100 dB | 6.6 mW | 1.0 mW |
| Voltage for 100 dB | 0.89 V | 0.22 V |
| Current for 100 dB | 7.4 mA | 4.6 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 15.00 Ω | 6.00 Ω |
| Sources that reach 100 dB out of 280 | 277 | 280 |
3 of the 280 sources have the power for the Beyerdynamic DT 900 Pro X but not for the AKG K612 Pro — Apple USB-C dongle (EU), Steinberg UR22C, Sony NW-A306.
17 sources are low enough in output impedance for the AKG K612 Pro under the one-eighth rule but not for the Beyerdynamic DT 900 Pro X (Zoom AMS-22, Arturia MiniFuse 2, Arturia MiniFuse 1, 14 more).
1 source stays below the audible-hiss threshold with the AKG K612 Pro but crosses it with the Beyerdynamic DT 900 Pro X (Schiit Mjolnir 3).
277 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 AKG K612 Pro is more demanding than 97% of the 567 non-electrostatic models in this database; the Beyerdynamic DT 900 Pro X than 62%. 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 | AKG K612 Pro power | AKG K612 Pro voltage | Beyerdynamic DT 900 Pro X power | Beyerdynamic DT 900 Pro X voltage |
|---|---|---|---|---|
| 80 | 0.07 mW | 89 mV | 0.01 mW | 22 mV |
| 85 | 0.21 mW | 0.16 V | 0.03 mW | 39 mV |
| 90 | 0.66 mW | 0.28 V | 0.10 mW | 69 mV |
| 95 | 2.1 mW | 0.50 V | 0.32 mW | 0.12 V |
| 100 | 6.6 mW | 0.89 V | 1.0 mW | 0.22 V |
| 105 | 21 mW | 1.58 V | 3.2 mW | 0.39 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, AKG K612 Pro | Headroom, Beyerdynamic DT 900 Pro X | Output impedance | Noise |
|---|---|---|---|---|---|
| JadeAudio JA11 | $20 | 0.8 dB | 13.0 dB | 0.5 Ω | 1.7 µV |
| FiiO KA11 | $29 | 9.1 dB | 21.3 dB | 0.7 Ω | 1.7 µV |
| FiiO BTR11 | $36 | 0.7 dB | 13.0 dB | 0.5 Ω | 8.0 µV |
Of the 280 sources here, 277 reach 100 dB on both. That is the easy axis. 69 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 205 of them are in the second group.
The cheapest of the 69 is the JadeAudio JA11, at $20. It leaves 0.8 dB of headroom on the AKG K612 Pro and 13.0 dB on the Beyerdynamic DT 900 Pro X, its output impedance is 0.5 Ω against a one-eighth limit of 15.00 Ω and 6.00 Ω, and its noise figure puts the hiss floor 34 dB and 22 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 |
|---|---|---|---|
| AKG K612 Pro | 12 - 39500 Hz | not printed | not printed |
| Beyerdynamic DT 900 Pro X | 5 - 40,000 Hz | not printed | not printed |
AKG prints 12 - 39500 Hz for the K612 Pro. Beyerdynamic prints 5 - 40,000 Hz for the DT 900 Pro X.
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: AKG K612 Pro and Beyerdynamic DT 900 Pro X. 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.