The 2000 Ohm High Impedance Headphones were made special for me by a manufacturer. As with anything special made and not purchasing 10 thousand or more of them at a time the cost was high.
The 2000 Ohm High Impedance Headphones are mono with 1/4 inch plug ends. The High Impedance Headphones have an Impedance of 2000 Ohm. The cord is about 30 inches long.
My crystal radio set with a 12ft antenna connected to it will operate the 2000 Ohm High Impedance Headset without the use of a matching transformer and the sound quality is much better than the sound from my ceramic earphones. However improved performance can be obtained if used with a matching transformer. A better option for a direct connection to a Crystal Radio without a matching transformer would be my Piezoelectric ( Ceramic Headphones ). The best impedance I have had others test the 2000 Ohm High Impedance Headphones at is around 8,000 to 11,000 ohms at 1Khz.
Because my primary sales are for Crystal Radios I sell these 2000 Ohm Headphones as Crystal Radio Headphones. However many Amateur Radio and Ham Radio operators use them.
2000 Ohm High Impedance Headphones are rare and hard to find. Most are older or antiques. These High Impedance Headphones are not studio quality but intended for general use and listening.
These High Impedance Headsets are light weight and have foam covered Headsets.
The 2000 Ohm High Impedance Headphones makes them usable with my MK484 AM Radio Ic without a audio amplifier. However a amplifier will produce much more volume.
Such high impedance headphones are called sound powered headphones.