Both are audio interfaces, $699 against $139. 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 18i20 4th gen reaches 100 dB on 553 of the 567 models here, the Focusrite Scarlett Solo 4th gen on 552.
| Specification | Focusrite Scarlett 18i20 4th gen | Focusrite Scarlett Solo 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 | $699 | $139 |
| 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.
| Load | Focusrite Scarlett 18i20 4th gen | Focusrite Scarlett Solo 4th gen |
|---|---|---|
| 32 Ω | Derived | Derived |
| 150 Ω | Derived | Derived |
| 300 Ω | Published | Published |
| 600 Ω | Derived | Derived |
Both makers publish a power rating, which is less common than the table above makes it look: of the 280 sources here, 209 publish a figure at at least one load and only 2 publish one at all four. Focusrite Scarlett 18i20 4th gen publishes at 300 Ω; Focusrite Scarlett Solo 4th gen at 300 Ω. Every other row is worked out from those — between two published loads, or beyond them holding voltage constant, which understates rather than flatters.
The two publish at the same loads, which is the one case where the rows of this table can be read straight across.
What each of these labels means, and why a derived figure is still worth printing, is set out in how this data was built.
1 headphone reaches 100 dB on the Focusrite Scarlett 18i20 4th gen but not on the Focusrite Scarlett Solo 4th gen — Kinera Freya Vanir.
41 headphones are left alone by the Focusrite Scarlett 18i20 4th gen under the one-eighth rule but coloured by the Focusrite Scarlett Solo 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.
The counts above say how many models the two treat differently. This says by how much. The same 8 headphones appear on every page of this kind, ordered from the easiest to drive to the hardest, so a row can be read across pages as well as across columns. Headroom is at a 100 dB SPL peak.
The widest gap on the list is the HiFiMAN HE400se: Focusrite Scarlett 18i20 4th gen has +7 dB of headroom there against +5 dB. 3 dB is about 1.8 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Focusrite Scarlett 18i20 4th gen and Focusrite Scarlett Solo 4th gen because neither maker publishes no output noise figure. That is a gap in the specification, not a quiet amplifier, and it is left blank here rather than filled with a plausible number.
| Headphone | Impedance | Needs | Focusrite Scarlett 18i20 4th gen headroom | Focusrite Scarlett Solo 4th gen headroom | Focusrite Scarlett 18i20 4th gen hiss | Focusrite Scarlett Solo 4th gen hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +26 dB damping | +23 dB damping | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +6 dB damping | +3 dB damping | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +16 dB damping | +14 dB damping | not published | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +16 dB | +15 dB damping | not published | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +7 dB damping | +5 dB damping | not published | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +10 dB | +9 dB | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +6 dB | +5 dB damping | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | -1 dB damping | -3 dB damping | not published | not published |
The Focusrite Scarlett 18i20 4th gen costs $560 more than the Focusrite Scarlett Solo 4th gen. Out of the 567 models here, that difference buys 1 more model driven to 100 dB and 41 more models left alone under the one-eighth rule.
Nothing runs the other way: there is no axis here on which the cheaper of the two does better.
Everything in this paragraph counts only figures the two makers published. An advantage on an axis one of them leaves blank cannot be counted, and is not counted — how often that happens is its own page.
Each has a page of its own with every power figure traced to what the maker published and a full headphone list: Focusrite Scarlett 18i20 4th gen and Focusrite Scarlett Solo 4th gen. Or put either against your own headphones in the source comparison tool.