The Audeze LCD-MX4 is 20Ω at 105.0 dB/mW; the Audeze MM-500 is 18Ω at 100.0 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 MM-500 needs 5.0 dB more than the LCD-MX4 to reach the same loudness — 1.0 mW against 0.32 mW.
| Specification | LCD-MX4 | MM-500 |
|---|---|---|
| Impedance | 20 Ω | 18 Ω |
| Sensitivity | 105.0 dB/mW | 100.0 dB/mW |
| Sensitivity (voltage) | 122.0 dB/V | 117.4 dB/V |
| Power for 100 dB | 0.32 mW | 1.0 mW |
| Voltage for 100 dB | 80 mV | 0.13 V |
| Current for 100 dB | 4.0 mA | 7.5 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 2.50 Ω | 2.25 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.
2 sources stay below the audible-hiss threshold with the MM-500 but cross it with the LCD-MX4 (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: Audeze LCD-MX4 and Audeze MM-500. Every figure on this page comes from what Audeze published, or is derived from it — what that maker publishes, counted.