Both are audio interfaces, $570 against $499. 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 MOTU M6 reaches 100 dB on 565 of the 567 models here, the Focusrite Scarlett 18i16 (4th Gen) on 553.
| Specification | Focusrite Scarlett 18i16 (4th Gen) | MOTU M6 |
|---|---|---|
| Power into 32Ω | 55 mW | 333 mW |
| Power into 150Ω | 27 mW | 71 mW |
| Power into 300Ω | 27 mW | 36 mW |
| Power into 600Ω | 14 mW | 18 mW |
| Output impedance | 11 Ω | not published |
| Output noise | not published | not published |
| Price | $570 | $499 |
| Headphones it reaches 100 dB on out of 567 | 553 | 565 |
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 18i16 (4th Gen) | MOTU M6 |
|---|---|---|
| 32 Ω | Derived | Upper bound |
| 150 Ω | Derived | Upper bound |
| 300 Ω | Published | Upper bound |
| 600 Ω | Derived | Upper bound |
These two columns are not the same kind of number, and that matters more than the gap between them. Focusrite Scarlett 18i16 (4th Gen) publishes a power rating (at 300 Ω); MOTU M6 publishes no power figure at any load, only a maximum output voltage, so every milliwatt in its column is a ceiling worked out from that voltage.
A ceiling assumes the amplifier holds that voltage into the load, and nothing on MOTU M6’s own sheet says it does. It is the most flattering reading available, and it is used here only because the alternative is a blank. Where the MOTU M6 column looks the stronger of the two, treat the difference as unproven rather than measured. 24 of the 280 sources here are in that position, with no published power rating at any load.
What each of these labels means, and why a derived figure is still worth printing, is set out in how this data was built.
12 headphones reach 100 dB on the MOTU M6 but not on the Focusrite Scarlett 18i16 (4th Gen) — HiFiMAN HE-6se V2, HiFiMAN HE6 Remastered, HiFiMAN Susvara, 9 more.
553 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: MOTU M6 has +15 dB of headroom there against +7 dB. 8 dB is about 6 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Focusrite Scarlett 18i16 (4th Gen) and MOTU M6 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 18i16 (4th Gen) headroom | MOTU M6 headroom | Focusrite Scarlett 18i16 (4th Gen) hiss | MOTU M6 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +26 dB damping | +34 dB | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +6 dB damping | +14 dB | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +16 dB damping | +23 dB | not published | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +16 dB | +18 dB | not published | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +7 dB damping | +15 dB | not published | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +10 dB | +12 dB | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +6 dB | +7 dB | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | -1 dB damping | +5 dB | not published | not published |
The Focusrite Scarlett 18i16 (4th Gen) costs $71 more than the MOTU M6, and on these three axes the money buys nothing: among the 567 models here there is not one that the Focusrite Scarlett 18i16 (4th Gen) handles and the MOTU M6 does not — not on power, not on the one-eighth rule, not on hiss. The traffic runs the other way: the cheaper MOTU M6 drives 12 models to 100 dB that the Focusrite Scarlett 18i16 (4th Gen) does not.
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 18i16 (4th Gen) and MOTU M6. Or put either against your own headphones in the source comparison tool.