Both are Bluetooth receivers, $90 against $109. 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 FiiO BTR15 reaches 100 dB on 565 of the 567 models here, the EarStudio ES100 MK2 on 553.
| Specification | EarStudio ES100 MK2 | FiiO BTR15 |
|---|---|---|
| Power into 32Ω | 60 mW | 125 mW |
| Power into 150Ω | 20 mW | 28 mW |
| Power into 300Ω | 10.0 mW | 15 mW |
| Power into 600Ω | 5.0 mW | 7.5 mW |
| Output impedance | 0.5 Ω unverified | 1.0 Ω |
| Output noise | 3 µV unverified | 2.0 µV |
| Price | $90 | $109 |
| 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 | EarStudio ES100 MK2 | FiiO BTR15 |
|---|---|---|
| 32 Ω | Unverified | Published |
| 150 Ω | Unverified | Derived |
| 300 Ω | Unverified | Published |
| 600 Ω | Unverified | Derived |
EarStudio ES100 MK2 publishes no electrical specification at all. That is true of 10 of the 280 sources here, and the figures in that column come from independent measurement rather than from a maker document — which is not worse, but it is not the same thing, and it cannot be checked against anything the maker will stand behind.
The FiiO BTR15 column does stand on a power rating its maker printed, at one of these four loads at least. Reading the two straight across sets one kind of claim against another, and nobody has written down the conditions of both side by side.
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 FiiO BTR15 but not on the EarStudio ES100 MK2 — 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 Shure SE846: FiiO BTR15 has +34 dB of headroom there against +26 dB. 7 dB is about 5.5 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for EarStudio ES100 MK2 because that 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 | EarStudio ES100 MK2 headroom | FiiO BTR15 headroom | EarStudio ES100 MK2 hiss | FiiO BTR15 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +26 dB | +34 dB | not published | 20 dB |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +6 dB | +14 dB | not published | 0 dB |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +16 dB | +19 dB | not published | -1 dB |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +13 dB | +14 dB | not published | -6 dB |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +8 dB | +12 dB | not published | -7 dB |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +6 dB | +8 dB | not published | -13 dB |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +2 dB | +4 dB | not published | -17 dB |
| HiFiMAN Susvara | 60 Ω | 50 mW | -1 dB | +1 dB | not published | -19 dB |
The FiiO BTR15 costs $19 more than the EarStudio ES100 MK2. Out of the 567 models here, that difference buys 12 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 a full headphone list and the provenance of every figure — worth opening here, because EarStudio ES100 MK2 has published no electrical specification at all and everything above comes from independent measurement: EarStudio ES100 MK2 and FiiO BTR15. Or put either against your own headphones in the source comparison tool.