If you love headphones and learning more about the technology behind them, check out Wikiphonia. It's a wiki dedicated solely to headphones (primarily rare and out of production models). Here's a bit about it from the site:
This Wiki contains 371 articles about various types of headphones and headphone related material. You can talk freely about any type of headphones new or old, dynamic, isodynamic (aka orthodynamic) or electrostatic.
My intention is to compile as much information about headphones for public use as possible, however I especially want to concentrate 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.
Fascinating read. Check it out here.