The Fostex T20RP MK3 is 50Ω at 92.0 dB/mW; the Fostex TH-X00 (Drop) is 25Ω at 100.0 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 T20RP MK3 needs 8.0 dB more than the TH-X00 (Drop) to reach the same loudness — 6.3 mW against 1.0 mW.
| Specification | T20RP MK3 | TH-X00 (Drop) |
|---|---|---|
| Impedance | 50 Ω | 25 Ω |
| Sensitivity | 92.0 dB/mW | 100.0 dB |
| Sensitivity (voltage) | 105.0 dB/V | 116.0 dB/V |
| Power for 100 dB | 6.3 mW | 1.0 mW |
| Voltage for 100 dB | 0.56 V | 0.16 V |
| Current for 100 dB | 11.2 mA | 6.3 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 6.25 Ω | 3.12 Ω |
| Sources that reach 100 dB out of 280 | 280 | 280 |
One caution before reading the rows. For Fostex TH-X00 (Drop) 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.
1 source is low enough in output impedance for the T20RP MK3 under the one-eighth rule but not for the TH-X00 (Drop) (Shanling H5).
1 source stays below the audible-hiss threshold with the T20RP MK3 but crosses it with the TH-X00 (Drop) (Schiit Mjolnir 3).
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 T20RP MK3 is more demanding than 88% of the 567 non-electrostatic models in this database; the TH-X00 (Drop) than 48%. 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 | T20RP MK3 power | T20RP MK3 voltage | TH-X00 (Drop) power | TH-X00 (Drop) voltage |
|---|---|---|---|---|
| 80 | 0.06 mW | 56 mV | 0.01 mW | 16 mV |
| 85 | 0.20 mW | 100 mV | 0.03 mW | 28 mV |
| 90 | 0.63 mW | 0.18 V | 0.10 mW | 50 mV |
| 95 | 2.0 mW | 0.32 V | 0.32 mW | 89 mV |
| 100 | 6.3 mW | 0.56 V | 1.0 mW | 0.16 V |
| 105 | 20 mW | 1.00 V | 3.2 mW | 0.28 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, T20RP MK3 | Headroom, TH-X00 (Drop) | Output impedance | Noise |
|---|---|---|---|---|---|
| JadeAudio JA11 | $20 | 4.8 dB | 13.7 dB | 0.5 Ω | 1.7 µV |
| FiiO KA11 | $29 | 13.1 dB | 23.2 dB | 0.7 Ω | 1.7 µV |
| FiiO BTR11 | $36 | 4.8 dB | 15.3 dB | 0.5 Ω | 8.0 µV |
Of the 280 sources here, 280 reach 100 dB on both. That is the easy axis. 69 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 69 is the JadeAudio JA11, at $20. It leaves 4.8 dB of headroom on the T20RP MK3 and 13.7 dB on the TH-X00 (Drop), its output impedance is 0.5 Ω against a one-eighth limit of 6.25 Ω and 3.12 Ω, and its noise figure puts the hiss floor 30 dB and 19 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.
Each model has a page of its own with the full source list, the hiss estimate and the provenance of every figure above: Fostex T20RP MK3 and Fostex TH-X00 (Drop). Each figure on this page is labelled on those pages with where it came from, including the ones Fostex never published — what that maker publishes, counted.