The Etymotic ER2XR is 15Ω at 96.0 dB/mW; the Etymotic ER3SE is 22Ω at 102.0 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 ER2XR needs 6.0 dB more than the ER3SE to reach the same loudness — 2.5 mW against 0.63 mW.
| Specification | ER2XR | ER3SE |
|---|---|---|
| Impedance | 15 Ω | 22 Ω |
| Sensitivity | 96.0 dB/mW | 102.0 dB/mW |
| Sensitivity (voltage) | 114.2 dB/V | 118.6 dB/V |
| Power for 100 dB | 2.5 mW | 0.63 mW |
| Voltage for 100 dB | 0.19 V | 0.12 V |
| Current for 100 dB | 12.9 mA | 5.4 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 1.88 Ω | 2.75 Ω |
| Sources that reach 100 dB out of 280 | 280 | 280 |
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.
3 sources are low enough in output impedance for the ER3SE under the one-eighth rule but not for the ER2XR (Astell&Kern HC3, RME Fireface UFX II, RME Fireface UFX III).
280 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: Etymotic ER2XR and Etymotic ER3SE. Every figure on this page comes from what Etymotic published, or is derived from it — what that maker publishes, counted.