This page does not review anything Ferrum 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.
| Product | Into 32Ω | Output impedance | Output noise |
|---|---|---|---|
| Ferrum OOR | 1.1 W | 0.3 Ω | 1.5 µV |
| Ferrum ERCO | 1.1 W | 0.3 Ω | not published |
Power decides whether it gets loud enough, output impedance decides whether it tilts the response of a multi-driver in-ear, and the noise figure decides whether you hear hiss with sensitive ones. All three fit on one line of a spec sheet; most of the industry prints one of them.
Ferrum publishes a power figure at a stated load on 2 of 2, output impedance on 2, a noise figure on 1. Of the 8 power figures this site displays for them at 32, 150, 300 and 600 Ω: 2 printed by Ferrum at that exact load, 6 worked out by holding output voltage steady across loads.
Most of what this site says about Ferrum came from them, with the rest derived and labelled as derived.
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.