Wikiphonia, held by Faust3d, contains hundreds articles about various types of headphones and headphone related material. People can talk freely and add information about any type of headphones new or old, dynamic, isodynamic (aka orthodynamic) or electrostatic.
The main focus of the wiki is on old out of production headphones such as Jecklin Floats, vintage Stax Earspeakers, MB Peerless headphones and other obscure and not so obscure headphones that deserve to be heard.
The link points to the Stax section, which I consider one of the best resources for knowing about Stax headphones and history.
All the other sections (like the orthodynamic section) are equally interesting to explore.