This page does not review anything Koss 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 |
|---|---|---|---|
| ESP/95X Plus | 100000 Ω | — | Reference not convertible |
| KPH30i | 60 Ω | 101.0 dB | Unit not stated |
| KPH40 Utility | 60 Ω | 101.0 dB | Unit not stated |
| KSC75 | 60 Ω | 101.0 dB/mW | Published per mW |
| Porta Pro | 60 Ω | 101.0 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 |
|---|---|---|---|
| ESP/95X Plus | 8-35,000 Hz | not printed | not printed |
| KPH30i | 15-25,000 Hz | not printed | not printed |
| KPH40 Utility | 15-25,000 Hz | not printed | not printed |
| KSC75 | 15-25,000 Hz | not printed | not printed |
| Porta Pro | 15-25,000 Hz | not printed | not printed |
Koss prints a frequency range for all 5 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 Koss with the majority: of the 490 models across this database whose maker prints a range, 58 print the tolerance.
Every range stands under the same heading, give or take a capital letter: “Frequency Response”.
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 4 to drive is the Koss KSC75: 0.79 mW and 0.22 V for a 100 dB SPL peak. Their impedances run from 60 to 60 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 4, 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 Koss KSC75 at 60 Ω, so a source wants an output impedance at or below 7.5 Ω to satisfy the one-eighth rule on everything they make. 135 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.
Rather less than half of what this site says about Koss came from them. The rest is arithmetic, and it is marked as arithmetic on every page.
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.