The Sennheiser HD 6XX (Drop) is 300Ω at 97.8 dB/mW; the ZMF Atrium is 300Ω at 96.0 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 ZMF Atrium needs 1.8 dB more than the Sennheiser HD 6XX (Drop) to reach the same loudness — 2.5 mW against 1.7 mW.
| Specification | Sennheiser HD 6XX (Drop) | ZMF Atrium |
|---|---|---|
| Impedance | 300 Ω | 300 Ω |
| Sensitivity | 97.8 dB/mW | 96.0 dB/mW |
| Sensitivity (voltage) | 103.0 dB/V | 101.2 dB/V |
| Power for 100 dB | 1.7 mW | 2.5 mW |
| Voltage for 100 dB | 0.71 V | 0.87 V |
| Current for 100 dB | 2.4 mA | 2.9 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 37.50 Ω | 37.50 Ω |
| Sources that reach 100 dB out of 280 | 280 | 277 |
3 of the 280 sources have the power for the Sennheiser HD 6XX (Drop) but not for the ZMF Atrium — Apple USB-C dongle (EU), Steinberg UR22C, Sony NW-A306.
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 ZMF Atrium is more demanding than 96% of the 567 non-electrostatic models in this database; the Sennheiser HD 6XX (Drop) than 93%. 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 | Sennheiser HD 6XX (Drop) power | Sennheiser HD 6XX (Drop) voltage | ZMF Atrium power | ZMF Atrium voltage |
|---|---|---|---|---|
| 80 | 0.02 mW | 71 mV | 0.03 mW | 87 mV |
| 85 | 0.05 mW | 0.13 V | 0.08 mW | 0.15 V |
| 90 | 0.17 mW | 0.22 V | 0.25 mW | 0.27 V |
| 95 | 0.52 mW | 0.40 V | 0.79 mW | 0.49 V |
| 100 | 1.7 mW | 0.71 V | 2.5 mW | 0.87 V |
| 105 | 5.2 mW | 1.25 V | 7.9 mW | 1.54 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, Sennheiser HD 6XX (Drop) | Headroom, ZMF Atrium | Output impedance | Noise |
|---|---|---|---|---|---|
| JadeAudio JA11 | $20 | 2.9 dB | 1.1 dB | 0.5 Ω | 1.7 µV |
| FiiO KA11 | $29 | 11.2 dB | 9.4 dB | 0.7 Ω | 1.7 µV |
| FiiO BTR11 | $36 | 2.6 dB | 0.8 dB | 0.5 Ω | 8.0 µV |
Of the 280 sources here, 277 reach 100 dB on both. That is the easy axis. 72 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 72 is the JadeAudio JA11, at $20. It leaves 2.9 dB of headroom on the Sennheiser HD 6XX (Drop) and 1.1 dB on the ZMF Atrium, its output impedance is 0.5 Ω against a one-eighth limit of 37.50 Ω for both, and its noise figure puts the hiss floor 32 dB and 34 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 |
|---|---|---|---|
| Sennheiser HD 6XX (Drop) | 10 Hz – 41 kHz | not printed | not printed |
| ZMF Atrium | nothing printed | — | — |
Sennheiser prints 10 Hz – 41 kHz for the HD 6XX (Drop). ZMF prints nothing at all for the Atrium.
So one side of this comparison has a frequency-response number and the other does not — which changes less than it looks. The range printed for the Sennheiser HD 6XX (Drop) comes with no tolerance beside it, and a range without a ±dB figure says nothing about how loud the headphone is at either end of it: thirty decibels down at the bottom and the sentence would still be true. On the only reading that would have made it a specification, the two sheets say the same amount: nothing.
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: Sennheiser HD 6XX (Drop) and ZMF Atrium. Every figure on this page comes from what Sennheiser and ZMF published, or is derived from it — what Sennheiser publishes and what ZMF publishes, both counted.