The Audio-Technica ATH-R70X is 470Ω at 98.0 dB/mW; the HiFiMAN Sundara is 32Ω at 92.0 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 HiFiMAN Sundara needs 6.0 dB more than the Audio-Technica ATH-R70X to reach the same loudness — 6.3 mW against 1.6 mW.
| Specification | Audio-Technica ATH-R70X | HiFiMAN Sundara |
|---|---|---|
| Impedance | 470 Ω | 32 Ω |
| Sensitivity | 98.0 dB/mW | 92.0 dB |
| Sensitivity (voltage) | 101.3 dB/V | 106.9 dB/V |
| Power for 100 dB | 1.6 mW | 6.3 mW |
| Voltage for 100 dB | 0.86 V | 0.45 V |
| Current for 100 dB | 1.8 mA | 14.0 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 58.75 Ω | 4.00 Ω |
| Sources that reach 100 dB out of 280 | 277 | 280 |
One caution before reading the rows. HiFiMAN Sundara 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.
3 of the 280 sources have the power for the HiFiMAN Sundara but not for the Audio-Technica ATH-R70X — Apple USB-C dongle (EU), Steinberg UR22C, Sony NW-A306.
33 sources are low enough in output impedance for the Audio-Technica ATH-R70X under the one-eighth rule but not for the HiFiMAN Sundara (Zoom AMS-22, Audient EVO 4, ART HeadAmp 4 Pro, 30 more).
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.
Each model has a page of its own with the full source list, the hiss estimate and the provenance of every figure above: Audio-Technica ATH-R70X and HiFiMAN Sundara. Each figure on this page is labelled on those pages with where it came from, including the ones Audio-Technica and HiFiMAN never published — what Audio-Technica publishes and what HiFiMAN publishes, both counted.