This page does not review anything Fostex makes. It counts one thing: how much of what this database says about their products came out of their own documents, and how much had to be worked out or left blank.
| Model | Impedance | Sensitivity | Source of the figure |
|---|---|---|---|
| T20RP MK3 | 50 Ω | 92.0 dB/mW | Published per mW |
| T40RP MK3 | 50 Ω | 91.0 dB/mW | Published per mW |
| T50RP MK3 | 50 Ω | 92.0 dB/mW | Published per mW |
| T50RP mk4 | 28 Ω | 97.0 dB/mW | Published per mW |
| T50RPmk4Q | 28 Ω | 97.0 dB/mW | Published per mW |
| T60RP | 50 Ω | 92.0 dB/mW | Published per mW |
| T60RPmk2 | 28 Ω | 96.0 dB/mW | Published per mW |
| TH-X00 (Drop) | 25 Ω | 100.0 dB | Not published |
| TH1000RPmk2 | 32 Ω | 100.0 dB/mW | Published per mW |
| TH1100RPmk2 | 32 Ω | 96.0 dB/mW | Published per mW |
| TH610 | 25 Ω | 98.0 dB/mW | Published per mW |
| TH616 | 25 Ω | 96.0 dB/mW | Published per mW |
| TH808 | 25 Ω | 100.0 dB/mW | Published per mW |
| TH818 | 25 Ω | 100.0 dB/mW | Published per mW |
| TH900 MK2 | 25 Ω | 100.0 dB/mW | Published per mW |
| TH909LE | 25 Ω | 100.0 dB/mW | Published per mW |
| TH919 | 25 Ω | 100.0 dB/mW | Published per mW |
Impedance is almost always printed. Sensitivity is the one that goes wrong, because a decibel figure means two very different things depending on whether it is per milliwatt or per volt — about five decibels apart at 300 Ω and eighteen at 16 Ω. The conversion is here.
| Model | As printed | Tolerance | Standard |
|---|---|---|---|
| T20RP MK3 | 15 to 35,000 Hz | not printed | not printed |
| T40RP MK3 | 20 to 35,000 Hz | not printed | not printed |
| T50RP MK3 | 15〜35,000Hz | not printed | not printed |
| T50RP mk4 | 10 to 40,000 Hz | not printed | not printed |
| T50RPmk4Q | 10–40,000 Hz | not printed | not printed |
| T60RP | 15 to 35,000 Hz | not printed | not printed |
| T60RPmk2 | 10～40,000 Hz | not printed | not printed |
| TH1000RPmk2 | 10 – 40,000 Hz | not printed | not printed |
| TH1100RPmk2 | 10 – 40,000 Hz | not printed | not printed |
| TH610 | 5 to 45,000 Hz | not printed | not printed |
| TH616 | 5 to 45,000Hz | not printed | not printed |
| TH808 | 5 to 45,000 Hz | not printed | not printed |
| TH818 | 12.5–45,000 Hz | not printed | not printed |
| TH900 MK2 | 5 to 45,000 Hz | not printed | not printed |
| TH909LE | 5 to 45,000 Hz | not printed | not printed |
| TH919 | 12.5 – 45,000 Hz | not printed | not printed |
Fostex prints a frequency range for all 16 models here whose sheets have been read.
Not one of those ranges comes with a tolerance in decibels. Without a ±dB figure a range says nothing about how loud the headphone is at either end of it, which puts Fostex with the majority: of the 490 models across this database whose maker prints a range, 58 print the tolerance.
The rows are not even called the same thing twice: 4 different headings across 16 models (“Frequency Response”, “Playback frequency band”, “Playback frequency range”, and more).
1 further model of theirs in this database has no page left on their site at all, so there is nothing to read for it either way. That is counted separately from printing nothing, because it is a different fact.
No measurement is published here — only what was printed. The whole count, maker by maker, is in the frequency response audit.
The hardest of the 17 to drive is the Fostex T40RP MK3: 7.9 mW and 0.63 V for a 100 dB SPL peak. Their impedances run from 25 to 50 Ω, which matters because the voltage a headphone wants rises with impedance while the power falls.
280 of the 280 sources here reach 100 dB on all 17, and the cheapest of them is the Apple USB-C dongle (EU) at $9. “Reaches” means the maker’s own published power figure is enough at that load; it is not a judgement of how it sounds.
Their lowest impedance is the Fostex TH-X00 (Drop) at 25 Ω, so a source wants an output impedance at or below 3.1 Ω to satisfy the one-eighth rule on everything they make. 134 of the 169 sources that publish an output impedance manage that.
These counts use figures the source makers published themselves. A product that publishes nothing is not counted as a pass anywhere above, which is why the three numbers differ so much. The collection matcher runs the same arithmetic over whatever you actually own.
Almost everything this site says about Fostex came from them. That is not the normal case and it is worth saying out loud.
The rule used here is the same for every maker and is described on the manufacturer index. Every figure behind it can be opened on the product page it came from, with the document it came from linked.