The Audio-Technica ATH-R70X is 470Ω at 98.0 dB/mW; the Audio-Technica ATH-R70xa is 470Ω at 97.0 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 ATH-R70xa needs 1.0 dB more than the ATH-R70X to reach the same loudness — 2.0 mW against 1.6 mW.
| Specification | ATH-R70X | ATH-R70xa |
|---|---|---|
| Impedance | 470 Ω | 470 Ω |
| Sensitivity | 98.0 dB/mW | 97.0 dB/mW |
| Sensitivity (voltage) | 101.3 dB/V | 100.3 dB/V |
| Power for 100 dB | 1.6 mW | 2.0 mW |
| Voltage for 100 dB | 0.86 V | 0.97 V |
| Current for 100 dB | 1.8 mA | 2.1 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 58.75 Ω | 58.75 Ω |
| Sources that reach 100 dB out of 280 | 277 | 275 |
2 of the 280 sources have the power for the ATH-R70X but not for the ATH-R70xa — FiiO BTR11, Sony NW-ZX707.
275 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 Audio-Technica ATH-R70xa. Every figure on this page comes from what Audio-Technica published, or is derived from it — what that maker publishes, counted.