The Grado Signature S550 is 38Ω at 112.0 dB/mW; the Grado SR125x is 38Ω at 98.0 dB/mW. This page covers what they ask of an amplifier, not how they sound.
The SR125x needs 14.0 dB more than the Signature S550 to reach the same loudness — 1.6 mW against 0.06 mW.
| Specification | Signature S550 | SR125x |
|---|---|---|
| Impedance | 38 Ω | 38 Ω |
| Sensitivity | 112.0 dB/mW | 98.0 dB/mW |
| Sensitivity (voltage) | 126.2 dB/V | 112.2 dB/V |
| Power for 100 dB | 0.06 mW | 1.6 mW |
| Voltage for 100 dB | 49 mV | 0.25 V |
| Current for 100 dB | 1.3 mA | 6.5 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.
16 sources stay below the audible-hiss threshold with the SR125x but cross it with the Signature S550 (FiiO BTR11, FiiO K11 R2R, Lake People G103-S Mk II, 13 more).
280 of the 280 sources here reach 100 dB on both.
The SR125x is more demanding than 66% of the 567 non-electrostatic models in this database; the Signature S550 than 10%.
| dB SPL | Signature S550 power | Signature S550 voltage | SR125x power | SR125x voltage |
|---|---|---|---|---|
| 80 | 0.6 µW | 5 mV | 0.02 mW | 25 mV |
| 85 | 2.0 µW | 9 mV | 0.05 mW | 44 mV |
| 90 | 6.3 µW | 15 mV | 0.16 mW | 78 mV |
| 95 | 0.02 mW | 28 mV | 0.50 mW | 0.14 V |
| 100 | 0.06 mW | 49 mV | 1.6 mW | 0.25 V |
| 105 | 0.20 mW | 87 mV | 5.0 mW | 0.44 V |
| Source | Price | Headroom, Signature S550 | Headroom, SR125x | Output impedance | Noise |
|---|---|---|---|---|---|
| JadeAudio JA11 | $20 | 26.0 dB | 12.0 dB | 0.5 Ω | 1.7 µV |
| FiiO KA11 | $29 | 34.3 dB | 20.3 dB | 0.7 Ω | 1.7 µV |
| FiiO BTR13 | $59 | 31.2 dB | 17.2 dB | 0.6 Ω | 1.0 µV |
Of the 280 sources here, 280 reach 100 dB on both. 55 of them also publish an output impedance low enough for both under the one-eighth rule and a noise figure that stays below the audible-hiss threshold with both.
The cheapest of the 55 is the JadeAudio JA11, at $20. It leaves 26.0 dB of headroom on the Signature S550 and 12.0 dB on the SR125x, its output impedance is 0.5 Ω against a one-eighth limit of 4.75 Ω for both, and its noise figure puts the hiss floor 9 dB and 23 dB below the 20 dB SPL this site treats as the point where a quiet room stops hiding it.
| Model | As printed | Tolerance | Standard |
|---|---|---|---|
| Signature S550 | 6Hz - 44kHz | not printed | not printed |
| SR125x | 20-20kHz | not printed | not printed |
Grado prints 6Hz - 44kHz for the Signature S550 and 20-20kHz for the SR125x.
Neither range has a tolerance printed beside it, so a wider range on one sheet is not deeper bass or more treble.
Not a measurement; maker by maker.
Both have a page of their own. In full: Grado Signature S550 and Grado SR125x. Every figure on this page comes from what Grado published, or is derived from it — what that maker publishes, counted.