The Etymotic ER4XR is 45Ω at 98.0 dB/mW; the Moondrop Aria is 32Ω at 107.1 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 Etymotic ER4XR needs 9.1 dB more than the Moondrop Aria to reach the same loudness — 1.6 mW against 0.19 mW.
| Specification | Etymotic ER4XR | Moondrop Aria |
|---|---|---|
| Impedance | 45 Ω | 32 Ω |
| Sensitivity | 98.0 dB/mW | 107.1 dB/mW |
| Sensitivity (voltage) | 111.5 dB/V | 122.0 dB/V |
| Power for 100 dB | 1.6 mW | 0.19 mW |
| Voltage for 100 dB | 0.27 V | 79 mV |
| Current for 100 dB | 5.9 mA | 2.5 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 5.62 Ω | 4.00 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.
1 source is low enough in output impedance for the Etymotic ER4XR under the one-eighth rule but not for the Moondrop Aria (Shanling H5).
2 sources stay below the audible-hiss threshold with the Etymotic ER4XR but cross it with the Moondrop Aria (FiiO BTR11, Rupert Neve RNHP).
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 ER4XR and Moondrop Aria. Every figure on this page comes from what Etymotic and Moondrop published, or is derived from it — what Etymotic publishes and what Moondrop publishes, both counted.