The HiFiMAN HE400i 2020 is 35Ω at 93.0 dB (no reference unit printed); the HiFiMAN Susvara Unveiled is 45Ω at 86.0 dB (no reference unit printed). 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 Susvara Unveiled needs 7.0 dB more than the HE400i 2020 to reach the same loudness — 25 mW against 5.0 mW.
| Specification | HE400i 2020 | Susvara Unveiled |
|---|---|---|
| Impedance | 35 Ω | 45 Ω |
| Sensitivity | 93.0 dB | 86.0 dB |
| Sensitivity (voltage) | 107.6 dB/V | 99.5 dB/V |
| Power for 100 dB | 5.0 mW | 25 mW |
| Voltage for 100 dB | 0.42 V | 1.06 V |
| Current for 100 dB | 12.0 mA | 23.6 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 4.38 Ω | 5.62 Ω |
| Sources that reach 100 dB out of 280 | 280 | 259 |
One caution before reading the rows. HiFiMAN HE400i 2020 and HiFiMAN Susvara Unveiled printed a decibel figure with no reference unit, so this page reads it as per milliwatt. If it is really per volt, each of them needs far more than the table says. Why the two readings differ by so much.
21 of the 280 sources have the power for the HE400i 2020 but not for the Susvara Unveiled — Apple USB-C dongle (US), Apple USB-C dongle (EU), JadeAudio JA11, 18 more.
1 source is low enough in output impedance for the Susvara Unveiled under the one-eighth rule but not for the HE400i 2020 (Shanling H5).
259 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 Susvara Unveiled is more demanding than 98% of the 567 non-electrostatic models in this database; the HE400i 2020 than 83%. 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 | HE400i 2020 power | HE400i 2020 voltage | Susvara Unveiled power | Susvara Unveiled voltage |
|---|---|---|---|---|
| 80 | 0.05 mW | 42 mV | 0.25 mW | 0.11 V |
| 85 | 0.16 mW | 74 mV | 0.79 mW | 0.19 V |
| 90 | 0.50 mW | 0.13 V | 2.5 mW | 0.34 V |
| 95 | 1.6 mW | 0.24 V | 7.9 mW | 0.60 V |
| 100 | 5.0 mW | 0.42 V | 25 mW | 1.06 V |
| 105 | 16 mW | 0.74 V | 79 mW | 1.89 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, HE400i 2020 | Headroom, Susvara Unveiled | Output impedance | Noise |
|---|---|---|---|---|---|
| FiiO KA11 | $29 | 15.6 dB | 7.5 dB | 0.7 Ω | 1.7 µV |
| FiiO BTR13 | $59 | 12.6 dB | 4.5 dB | 0.6 Ω | 1.0 µV |
| iBasso DC03 Pro | $69 | 12.5 dB | 4.4 dB | 0.12 Ω | 0.9 µV |
Of the 280 sources here, 259 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 189 of them are in the second group.
The cheapest of the 68 is the FiiO KA11, at $29. It leaves 15.6 dB of headroom on the HE400i 2020 and 7.5 dB on the Susvara Unveiled, its output impedance is 0.7 Ω against a one-eighth limit of 4.38 Ω and 5.62 Ω, and its noise figure puts the hiss floor 28 dB and 36 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 |
|---|---|---|---|
| HE400i 2020 | 20Hz-35KHz | not printed | not printed |
| Susvara Unveiled | 6Hz - 75kHz | not printed | not printed |
HiFiMAN prints 20Hz-35KHz for the HE400i 2020 and 6Hz - 75kHz for the Susvara Unveiled.
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: HiFiMAN HE400i 2020 and HiFiMAN Susvara Unveiled. Each figure on this page is labelled on those pages with where it came from, including the ones HiFiMAN never published — what that maker publishes, counted.