These are piezoelectric high impedance ceramic headphones. They have 1/4 inch mono plug end and their cord is approximately 4.5 feet long. These have an earcup that helps mute surrounding sound. The headband is expandable.
Piezoelectric headphones and earphones are very good for crystal radios.
These are made in the United States from imported parts.
Please note that if these are not operated from a transformer they need a resistor across the headphone input. Most crystal radios have a resistor in the audio output, if not add a 47K to 100K resistor in parallel.
Don’t forget a mono jack. Click here for details