The Thieaudio Monarch MKIV is 10Ω at 100.0 dB (no reference unit printed); the Thieaudio Oracle MKII is 15Ω at 104.0 dB (no figure from the maker at all). This page is only about what they ask of an amplifier — not how they sound, which no specification on either sheet can tell you.
The Monarch MKIV needs 4.0 dB more than the Oracle MKII to reach the same loudness — 1.0 mW against 0.40 mW.
| Specification | Monarch MKIV | Oracle MKII |
|---|---|---|
| Impedance | 10 Ω | 15 Ω |
| Sensitivity | 100.0 dB | 104.0 dB |
| Sensitivity (voltage) | 120.0 dB/V | 122.2 dB/V |
| Power for 100 dB | 1.0 mW | 0.40 mW |
| Voltage for 100 dB | 0.10 V | 77 mV |
| Current for 100 dB | 10.0 mA | 5.2 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 1.25 Ω | 1.88 Ω |
| Sources that reach 100 dB out of 280 | 280 | 280 |
One caution before reading the rows. Thieaudio Monarch MKIV printed a decibel figure with no reference unit, so this page reads it as per milliwatt. If it is really per volt, that model needs far more than the table says. Why the two readings differ by so much. For Thieaudio Oracle MKII the maker publishes no sensitivity figure at all. The number in the table was collected when this database was first built and has never been traced to a manufacturer document, so treat every row below it as an estimate rather than a specification.
Every source in the database that drives one of them drives the other. On power, the choice between these two changes nothing about what amplifier you need.
5 sources are low enough in output impedance for the Oracle MKII under the one-eighth rule but not for the Monarch MKIV (FiiO KA13, Schiit Vali 2+, FiiO M11S, 2 more).
2 sources stay below the audible-hiss threshold with the Monarch MKIV but cross it with the Oracle MKII (FiiO BTR11, Rupert Neve RNHP).
280 of the 280 sources here reach 100 dB on both. That count is about power only — the output-impedance and hiss lines above are separate questions, and a source can pass this one and fail those.
The gap between these two in decibels does not change with volume — it is a property of the two headphones. What changes is the size of the numbers, and it changes fast: every 10 dB costs ten times the power. The row that matters is the one nearest the level you listen at, and for most people that is nearer the top of this table than the bottom.
The Monarch MKIV is more demanding than 32% of the 567 non-electrostatic models in this database; the Oracle MKII than 24%. Both figures use the same measure as the rest of the site: whichever runs out first against a 2 V, 100 mW dongle, voltage or power.
| dB SPL | Monarch MKIV power | Monarch MKIV voltage | Oracle MKII power | Oracle MKII voltage |
|---|---|---|---|---|
| 80 | 0.01 mW | 10 mV | 4.0 µW | 8 mV |
| 85 | 0.03 mW | 18 mV | 0.01 mW | 14 mV |
| 90 | 0.10 mW | 32 mV | 0.04 mW | 24 mV |
| 95 | 0.32 mW | 56 mV | 0.13 mW | 43 mV |
| 100 | 1.0 mW | 0.10 V | 0.40 mW | 77 mV |
| 105 | 3.2 mW | 0.18 V | 1.3 mW | 0.14 V |
105 dB is included because forum power figures are usually quoted there or higher. It is also a level that damages hearing in minutes — how many minutes is its own calculator.
| Source | Price | Headroom, Monarch MKIV | Headroom, Oracle MKII | Output impedance | Noise |
|---|---|---|---|---|---|
| JadeAudio JA11 | $20 | 9.7 dB | 15.5 dB | 0.5 Ω | 1.7 µV |
| FiiO KA11 | $29 | 21.9 dB | 27.6 dB | 0.7 Ω | 1.7 µV |
| FiiO BTR13 | $59 | 18.8 dB | 24.5 dB | 0.6 Ω | 1.0 µV |
Of the 280 sources here, 280 reach 100 dB on both. That is the easy axis. 63 of them also publish an output impedance low enough for both under the one-eighth rule and a noise figure that stays below the audible-hiss threshold with both — the rest either fail one of those or never printed the number at all, and 208 of them are in the second group.
The cheapest of the 63 is the JadeAudio JA11, at $20. It leaves 9.7 dB of headroom on the Monarch MKIV and 15.5 dB on the Oracle MKII, its output impedance is 0.5 Ω against a one-eighth limit of 1.25 Ω and 1.88 Ω, and its noise figure puts the hiss floor 15 dB and 13 dB below the 20 dB SPL this site treats as the point where a quiet room stops hiding it.
Cheapest that satisfies three published numbers is not the same as best, and none of it is about how either headphone sounds. To put either model against a source this page does not mention, or to change the target loudness, use the amplifier matcher.
| Model | As printed | Tolerance | Standard |
|---|---|---|---|
| Monarch MKIV | 10Hz – 44kHz | not printed | not printed |
| Oracle MKII | nothing printed | — | — |
Thieaudio prints 10Hz – 44kHz for the Monarch MKIV and nothing at all for the Oracle MKII.
Oracle MKII: Thieaudio publishes a measured frequency-response graph for this model on the same page. What it does not publish is a range: there is no row of numbers to read the graph against.
So one side of this comparison has a frequency-response number and the other does not — which changes less than it looks. The range printed for the Monarch MKIV comes with no tolerance beside it, and a range without a ±dB figure says nothing about how loud the headphone is at either end of it: thirty decibels down at the bottom and the sentence would still be true. On the only reading that would have made it a specification, the two sheets say the same amount: nothing.
None of this is a measurement. What each maker publishes, and what it is worth, is set out in the frequency response audit.
Each model has a page of its own with the full source list, the hiss estimate and the provenance of every figure above: Thieaudio Monarch MKIV and Thieaudio Oracle MKII. Each figure on this page is labelled on those pages with where it came from, including the ones Thieaudio never published — what that maker publishes, counted.