The Sennheiser HD 280 Pro is 64Ω at 113.0 dB (no reference unit printed); the Sennheiser HD 400 PRO is 120Ω at 100.8 dB/mW. This page covers what they ask of an amplifier, not how they sound.
The HD 400 PRO needs 12.2 dB more than the HD 280 Pro to reach the same loudness — 0.83 mW against 0.05 mW.
| Specification | HD 280 Pro | HD 400 PRO |
|---|---|---|
| Impedance | 64 Ω | 120 Ω |
| Sensitivity | 113.0 dB | 100.8 dB/mW |
| Sensitivity (voltage) | 124.9 dB/V | 110.0 dB/V |
| Power for 100 dB | 0.05 mW | 0.83 mW |
| Voltage for 100 dB | 57 mV | 0.32 V |
| Current for 100 dB | 0.9 mA | 2.6 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 8.00 Ω | 15.00 Ω |
| Sources that reach 100 dB out of 280 | 280 | 280 |
One caution before reading the rows. Sennheiser HD 280 Pro 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.
Every source in the database that drives one of them drives the other. On power, the choice between these two changes nothing about what amplifier you need.
17 sources are low enough in output impedance for the HD 400 PRO under the one-eighth rule but not for the HD 280 Pro (Zoom AMS-22, Arturia MiniFuse 2, Arturia MiniFuse 1, 14 more).
10 sources stay below the audible-hiss threshold with the HD 400 PRO but cross it with the HD 280 Pro (FiiO BTR11, FiiO K11 R2R, Lake People G103-S Mk II, 7 more).
280 of the 280 sources here reach 100 dB on both.
The HD 400 PRO is more demanding than 77% of the 567 non-electrostatic models in this database; the HD 280 Pro than 16%.
| dB SPL | HD 280 Pro power | HD 280 Pro voltage | HD 400 PRO power | HD 400 PRO voltage |
|---|---|---|---|---|
| 80 | 0.5 µW | 6 mV | 8.3 µW | 32 mV |
| 85 | 1.6 µW | 10 mV | 0.03 mW | 56 mV |
| 90 | 5.0 µW | 18 mV | 0.08 mW | 100 mV |
| 95 | 0.02 mW | 32 mV | 0.26 mW | 0.18 V |
| 100 | 0.05 mW | 57 mV | 0.83 mW | 0.32 V |
| 105 | 0.16 mW | 0.10 V | 2.6 mW | 0.56 V |
| Source | Price | Headroom, HD 280 Pro | Headroom, HD 400 PRO | Output impedance | Noise |
|---|---|---|---|---|---|
| JadeAudio JA11 | $20 | 24.8 dB | 9.8 dB | 0.5 Ω | 1.7 µV |
| FiiO KA11 | $29 | 33.0 dB | 18.1 dB | 0.7 Ω | 1.7 µV |
| FiiO BTR13 | $59 | 30.0 dB | 15.0 dB | 0.6 Ω | 1.0 µV |
Of the 280 sources here, 280 reach 100 dB on both. 62 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 62 is the JadeAudio JA11, at $20. It leaves 24.8 dB of headroom on the HD 280 Pro and 9.8 dB on the HD 400 PRO, its output impedance is 0.5 Ω against a one-eighth limit of 8.00 Ω and 15.00 Ω, and its noise figure puts the hiss floor 10 dB and 25 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 280 Pro | 8 - 25,000 Hz | not printed | not printed |
| HD 400 PRO | 6 - 38,000 Hz (-10 dB) | -10 dB | not printed |
Sennheiser prints 8 - 25,000 Hz for the HD 280 Pro and 6 - 38,000 Hz (-10 dB) for the HD 400 PRO.
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 280 Pro 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 280 Pro and Sennheiser HD 400 PRO. Each figure on this page is labelled on those pages with where it came from, including the ones Sennheiser never published — what that maker publishes, counted.