Both are audio interfaces, $219 against $210. 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 M2 reaches 100 dB on 565 of the 567 models here, the Roland Rubix22 on 542.
| Specification | MOTU M2 | Roland Rubix22 |
|---|---|---|
| Power into 32Ω | 333 mW | 19 mW |
| Power into 150Ω | 71 mW | 15 mW |
| Power into 300Ω | 36 mW | 9.4 mW |
| Power into 600Ω | 18 mW | 5.4 mW |
| Output impedance | not published | 47 Ω |
| Output noise | not published | not published |
| Price | $219 | $210 |
| Headphones it reaches 100 dB on out of 567 | 565 | 542 |
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 | MOTU M2 | Roland Rubix22 |
|---|---|---|
| 32 Ω | Upper bound | Derived |
| 150 Ω | Upper bound | Derived |
| 300 Ω | Upper bound | Derived |
| 600 Ω | Upper bound | Derived |
Neither column is a power rating, and the two are not even weak in the same way. The MOTU M2 figures are ceilings worked out from a maximum output voltage, on the assumption that the amplifier holds it into the load. The Roland Rubix22 figures are worked out from figures its maker did publish — power at other loads, or the voltage printed beside it. The second method understates; the first flatters. That is the wrong way round for reading the table straight across, so a gap in favour of the MOTU M2 is the one to doubt.
What each of these labels means, and why a derived figure is still worth printing, is set out in how this data was built.
23 headphones reach 100 dB on the MOTU M2 but not on the Roland Rubix22 — Audeze LCD-5, Dan Clark Audio AEON 2 Closed, Dan Clark Audio AEON 2 Noire, 20 more.
542 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 M2 has +15 dB of headroom there against +3 dB. 12 dB is about 17 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for MOTU M2 and Roland Rubix22 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 | MOTU M2 headroom | Roland Rubix22 headroom | MOTU M2 hiss | Roland Rubix22 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +34 dB | +21 dB damping | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +14 dB | +1 dB damping | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +23 dB | +13 dB damping | not published | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +18 dB | +12 dB damping | not published | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +15 dB | +3 dB damping | not published | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +12 dB | +6 dB | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +7 dB | +2 dB damping | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +5 dB | -4 dB damping | not published | not published |
The MOTU M2 costs $9 more than the Roland Rubix22. Out of the 567 models here, that difference buys 23 more models driven to 100 dB.
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: MOTU M2 and Roland Rubix22. Or put either against your own headphones in the source comparison tool.