2000 Ohm Headphones in use by WB6FZH with his 1923 Parkin Crystal Radio.

Blonder-Tongue man, Ben Tongue has written some useful articles on using headphones with crystal radios.

Scott Balderson has a Headphone Museum and phones for sale. Also Crystal Radios and Test Equipment.

You have to JOIN first but then you will see the archives with a lot of useful data and discussions about hi-z headphones.

Offers tube type technology instead of solid state and digital electronics. Also includes classic and military radio pictures, and information.