The Meze 105 AER is 42Ω at 112.0 dB/mW; the Meze 99 Classics (2nd Gen) is 16Ω at 103.0 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 99 Classics (2nd Gen) needs 9.0 dB more than the 105 AER to reach the same loudness — 0.50 mW against 0.06 mW.
| Specification | 105 AER | 99 Classics (2nd Gen) |
|---|---|---|
| Impedance | 42 Ω | 16 Ω |
| Sensitivity | 112.0 dB/mW | 103.0 dB/mW |
| Sensitivity (voltage) | 125.8 dB/V | 121.0 dB/V |
| Power for 100 dB | 0.06 mW | 0.50 mW |
| Voltage for 100 dB | 51 mV | 90 mV |
| Current for 100 dB | 1.2 mA | 5.6 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 5.25 Ω | 2.00 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 105 AER under the one-eighth rule but not for the 99 Classics (2nd Gen) (Shanling H5).
13 sources stay below the audible-hiss threshold with the 99 Classics (2nd Gen) but cross it with the 105 AER (FiiO BTR11, FiiO K11 R2R, Lake People G103-S Mk II, 10 more).
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: Meze 105 AER and Meze 99 Classics (2nd Gen). Every figure on this page comes from what Meze published, or is derived from it — what that maker publishes, counted.