The AKG K240 MKII is 55Ω at 91.4 dB/mW; the AKG K612 Pro is 120Ω at 91.8 dB/mW. This page covers what they ask of an amplifier, not how they sound.
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 | K240 MKII | K612 Pro |
|---|---|---|
| Impedance | 55 Ω | 120 Ω |
| Sensitivity | 91.4 dB/mW | 91.8 dB/mW |
| Sensitivity (voltage) | 104.0 dB/V | 101.0 dB/V |
| Power for 100 dB | 7.2 mW | 6.6 mW |
| Voltage for 100 dB | 0.63 V | 0.89 V |
| Current for 100 dB | 11.5 mA | 7.4 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 6.88 Ω | 15.00 Ω |
| Sources that reach 100 dB out of 280 | 280 | 277 |
3 of the 280 sources have the power for the K240 MKII but not for the K612 Pro — Apple USB-C dongle (EU), Steinberg UR22C, Sony NW-A306.
17 sources are low enough in output impedance for the K612 Pro under the one-eighth rule but not for the K240 MKII (Zoom AMS-22, Arturia MiniFuse 2, Arturia MiniFuse 1, 14 more).
277 of the 280 sources here reach 100 dB on both.
The K612 Pro is more demanding than 97% of the 567 non-electrostatic models in this database; the K240 MKII than 92%.
| dB SPL | K240 MKII power | K240 MKII voltage | K612 Pro power | K612 Pro voltage |
|---|---|---|---|---|
| 80 | 0.07 mW | 63 mV | 0.07 mW | 89 mV |
| 85 | 0.23 mW | 0.11 V | 0.21 mW | 0.16 V |
| 90 | 0.72 mW | 0.20 V | 0.66 mW | 0.28 V |
| 95 | 2.3 mW | 0.35 V | 2.1 mW | 0.50 V |
| 100 | 7.2 mW | 0.63 V | 6.6 mW | 0.89 V |
| 105 | 23 mW | 1.12 V | 21 mW | 1.58 V |
| Source | Price | Headroom, K240 MKII | Headroom, K612 Pro | Output impedance | Noise |
|---|---|---|---|---|---|
| JadeAudio JA11 | $20 | 3.8 dB | 0.8 dB | 0.5 Ω | 1.7 µV |
| FiiO KA11 | $29 | 12.1 dB | 9.1 dB | 0.7 Ω | 1.7 µV |
| FiiO BTR11 | $36 | 3.8 dB | 0.7 dB | 0.5 Ω | 8.0 µV |
Of the 280 sources here, 277 reach 100 dB on both. 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 cheapest of the 70 is the JadeAudio JA11, at $20. It leaves 3.8 dB of headroom on the K240 MKII and 0.8 dB on the K612 Pro, its output impedance is 0.5 Ω against a one-eighth limit of 6.88 Ω and 15.00 Ω, and its noise figure puts the hiss floor 31 dB and 34 dB below the 20 dB SPL this site treats as the point where a quiet room stops hiding it.
| Model | As printed | Tolerance | Standard |
|---|---|---|---|
| K240 MKII | 15 - 25000 | not printed | not printed |
| K612 Pro | 12 - 39500 Hz | not printed | not printed |
AKG prints 15 - 25000 for the K240 MKII and 12 - 39500 Hz for the K612 Pro.
Neither range has a tolerance printed beside it, so a wider range on one sheet is not deeper bass or more treble.
Not a measurement; maker by maker.
Both have a page of their own. In full: AKG K240 MKII and AKG K612 Pro. Every figure on this page comes from what AKG published, or is derived from it — what that maker publishes, counted.