Both are audio interfaces, $570 against $199. This page puts them side by side on the only three things a maker can be held to — power, output impedance and noise — and then asks the question that actually matters: which headphones do they treat differently?
The Focusrite Scarlett 18i16 (4th Gen) reaches 100 dB on 553 of the 567 models here, the Focusrite Scarlett 2i2 4th gen on 552.
| Specification | Focusrite Scarlett 18i16 (4th Gen) | Focusrite Scarlett 2i2 4th gen |
|---|---|---|
| Power into 32Ω | 55 mW | 31 mW |
| Power into 150Ω | 27 mW | 19 mW |
| Power into 300Ω | 27 mW | 22 mW |
| Power into 600Ω | 14 mW | 11 mW |
| Output impedance | 11 Ω | 50 Ω |
| Output noise | not published | not published |
| Price | $570 | $199 |
| Headphones it reaches 100 dB on out of 567 | 553 | 552 |
A figure marked not published is missing from the maker’s own material, which is not the same as being good or bad. Where one of these two publishes a number and the other does not, the comparison on that axis cannot be made at all — and saying so is more useful than guessing.
1 headphone reaches 100 dB on the Focusrite Scarlett 18i16 (4th Gen) but not on the Focusrite Scarlett 2i2 4th gen — Kinera Freya Vanir.
41 headphones are left alone by the Focusrite Scarlett 18i16 (4th Gen) under the one-eighth rule but coloured by the Focusrite Scarlett 2i2 4th gen (AKG K612 Pro, Audeze LCD-3, Audeze LCD-4, 38 more).
552 of the 567 models here reach 100 dB on both. That is a power count and nothing more; whether either source suits a given headphone also depends on the two lines above.
Each has a page of its own with every power figure traced to what the maker published and a full headphone list: Focusrite Scarlett 18i16 (4th Gen) and Focusrite Scarlett 2i2 4th gen. Or put either against your own headphones in the source comparison tool.