The AKG K612 Pro is 120Ω at 91.8 dB/mW; the Sennheiser HD 600 is 300Ω at 91.8 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.
In amplifier terms these two are the same headphone. The gap between what they need for 100 dB is under half a decibel, which is smaller than the step between two clicks of most volume controls.
| Specification | AKG K612 Pro | Sennheiser HD 600 |
|---|---|---|
| Impedance | 120 Ω | 300 Ω |
| Sensitivity | 91.8 dB/mW | 91.8 dB/mW |
| Sensitivity (voltage) | 101.0 dB/V | 97.0 dB/V |
| Power for 100 dB | 6.6 mW | 6.6 mW |
| Voltage for 100 dB | 0.89 V | 1.41 V |
| Current for 100 dB | 7.4 mA | 4.7 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 15.00 Ω | 37.50 Ω |
| Sources that reach 100 dB out of 280 | 277 | 261 |
16 of the 280 sources have the power for the AKG K612 Pro but not for the Sennheiser HD 600 — Apple USB-C dongle (US), JadeAudio JA11, FiiO SnowSky Tiny A, 13 more.
2 sources are low enough in output impedance for the Sennheiser HD 600 under the one-eighth rule but not for the AKG K612 Pro (Schiit Valhalla 3, Arturia AudioFuse Rev2).
261 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 Sennheiser HD 600 is more demanding than 99% of the 567 non-electrostatic models in this database; the AKG K612 Pro than 97%. 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 | Sennheiser HD 600 power | Sennheiser HD 600 voltage |
|---|---|---|---|---|
| 80 | 0.07 mW | 89 mV | 0.07 mW | 0.14 V |
| 85 | 0.21 mW | 0.16 V | 0.21 mW | 0.25 V |
| 90 | 0.66 mW | 0.28 V | 0.66 mW | 0.45 V |
| 95 | 2.1 mW | 0.50 V | 2.1 mW | 0.79 V |
| 100 | 6.6 mW | 0.89 V | 6.6 mW | 1.41 V |
| 105 | 21 mW | 1.58 V | 21 mW | 2.50 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, Sennheiser HD 600 | Output impedance | Noise |
|---|---|---|---|---|---|
| FiiO KA11 | $29 | 9.1 dB | 5.2 dB | 0.7 Ω | 1.7 µV |
| FiiO BTR13 | $59 | 6.0 dB | 1.8 dB | 0.6 Ω | 1.0 µV |
| iBasso DC03 Pro | $69 | 6.0 dB | 2.0 dB | 0.12 Ω | 0.9 µV |
Of the 280 sources here, 261 reach 100 dB on both. That is the easy axis. 68 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 192 of them are in the second group.
The cheapest of the 68 is the FiiO KA11, at $29. It leaves 9.1 dB of headroom on the AKG K612 Pro and 5.2 dB on the Sennheiser HD 600, its output impedance is 0.7 Ω against a one-eighth limit of 15.00 Ω and 37.50 Ω, and its noise figure puts the hiss floor 34 dB and 38 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 |
| Sennheiser HD 600 | 12 Hz - 40,500 Hz | not printed | not printed |
AKG prints 12 - 39500 Hz for the K612 Pro. Sennheiser prints 12 Hz - 40,500 Hz for the HD 600.
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 Sennheiser HD 600. Every figure on this page comes from what AKG and Sennheiser published, or is derived from it — what AKG publishes and what Sennheiser publishes, both counted.