The Sennheiser IE 200 is 18Ω at 101.6 dB/mW; the Sennheiser IE 300 is 16Ω at 106.0 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 IE 200 needs 4.4 dB more than the IE 300 to reach the same loudness — 0.69 mW against 0.25 mW.
| Specification | IE 200 | IE 300 |
|---|---|---|
| Impedance | 18 Ω | 16 Ω |
| Sensitivity | 101.6 dB/mW | 106.0 dB/mW |
| Sensitivity (voltage) | 119.0 dB/V | 124.0 dB/V |
| Power for 100 dB | 0.69 mW | 0.25 mW |
| Voltage for 100 dB | 0.11 V | 63 mV |
| Current for 100 dB | 6.2 mA | 4.0 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 2.25 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.
4 sources stay below the audible-hiss threshold with the IE 200 but cross it with the IE 300 (FiiO BTR11, FiiO K11 R2R, Lake People G111 Mk II, 1 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: Sennheiser IE 200 and Sennheiser IE 300. Every figure on this page comes from what Sennheiser published, or is derived from it — what that maker publishes, counted.