The Sennheiser HD 400 PRO is 120Ω at 100.8 dB/mW; the Sennheiser HD 600 is 300Ω at 91.8 dB/mW. This page covers what they ask of an amplifier, not how they sound.
The HD 600 needs 9.0 dB more than the HD 400 PRO to reach the same loudness — 6.6 mW against 0.83 mW.
| Specification | HD 400 PRO | HD 600 |
|---|---|---|
| Impedance | 120 Ω | 300 Ω |
| Sensitivity | 100.8 dB/mW | 91.8 dB/mW |
| Sensitivity (voltage) | 110.0 dB/V | 97.0 dB/V |
| Power for 100 dB | 0.83 mW | 6.6 mW |
| Voltage for 100 dB | 0.32 V | 1.41 V |
| Current for 100 dB | 2.6 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 | 280 | 261 |
19 of the 280 sources have the power for the HD 400 PRO but not for the HD 600 — Apple USB-C dongle (US), Apple USB-C dongle (EU), JadeAudio JA11, 16 more.
2 sources are low enough in output impedance for the HD 600 under the one-eighth rule but not for the HD 400 PRO (Schiit Valhalla 3, Arturia AudioFuse Rev2).
261 of the 280 sources here reach 100 dB on both.
The HD 600 is more demanding than 99% of the 567 non-electrostatic models in this database; the HD 400 PRO than 77%.
| dB SPL | HD 400 PRO power | HD 400 PRO voltage | HD 600 power | HD 600 voltage |
|---|---|---|---|---|
| 80 | 8.3 µW | 32 mV | 0.07 mW | 0.14 V |
| 85 | 0.03 mW | 56 mV | 0.21 mW | 0.25 V |
| 90 | 0.08 mW | 100 mV | 0.66 mW | 0.45 V |
| 95 | 0.26 mW | 0.18 V | 2.1 mW | 0.79 V |
| 100 | 0.83 mW | 0.32 V | 6.6 mW | 1.41 V |
| 105 | 2.6 mW | 0.56 V | 21 mW | 2.50 V |
| Source | Price | Headroom, HD 400 PRO | Headroom, HD 600 | Output impedance | Noise |
|---|---|---|---|---|---|
| FiiO KA11 | $29 | 18.1 dB | 5.2 dB | 0.7 Ω | 1.7 µV |
| FiiO BTR13 | $59 | 15.0 dB | 1.8 dB | 0.6 Ω | 1.0 µV |
| iBasso DC03 Pro | $69 | 15.0 dB | 2.0 dB | 0.12 Ω | 0.9 µV |
Of the 280 sources here, 261 reach 100 dB on both. 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 cheapest of the 68 is the FiiO KA11, at $29. It leaves 18.1 dB of headroom on the HD 400 PRO and 5.2 dB on the 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 25 dB and 38 dB below the 20 dB SPL this site treats as the point where a quiet room stops hiding it.
| Model | As printed | Tolerance | Standard |
|---|---|---|---|
| HD 400 PRO | 6 - 38,000 Hz (-10 dB) | -10 dB | not printed |
| HD 600 | 12 Hz - 40,500 Hz | not printed | not printed |
Sennheiser prints 6 - 38,000 Hz (-10 dB) for the HD 400 PRO and 12 Hz - 40,500 Hz for the HD 600.
Only one of the two is a specification. The range printed for the HD 400 PRO comes with a tolerance; the one printed for the HD 600 does not, and a range without a ±dB figure says nothing about how loud that model is at either end of it. The two cannot be compared number against number, however similar they look in the table. Of the 490 models whose maker prints a range, 58 print the tolerance.
Not a measurement; maker by maker.
Both have a page of their own. In full: Sennheiser HD 400 PRO and Sennheiser HD 600. Every figure on this page comes from what Sennheiser published, or is derived from it — what that maker publishes, counted.