The Grado GS3000x is 38Ω at 99.8 dB/mW; the Grado Signature S950 is 38Ω at 117.0 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 GS3000x needs 17.2 dB more than the Signature S950 to reach the same loudness — 1.0 mW against 0.02 mW.
| Specification | GS3000x | Signature S950 |
|---|---|---|
| Impedance | 38 Ω | 38 Ω |
| Sensitivity | 99.8 dB/mW | 117.0 dB/mW |
| Sensitivity (voltage) | 114.0 dB/V | 131.2 dB/V |
| Power for 100 dB | 1.0 mW | 0.02 mW |
| Voltage for 100 dB | 0.20 V | 28 mV |
| Current for 100 dB | 5.2 mA | 0.7 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 4.75 Ω | 4.75 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.
27 sources stay below the audible-hiss threshold with the GS3000x but cross it with the Signature S950 (Kiwi Ears Allegro Mini, FiiO BTR11, FiiO K11, 24 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: Grado GS3000x and Grado Signature S950. Every figure on this page comes from what Grado published, or is derived from it — what that maker publishes, counted.