During World War II, GIs in the field built really amazing simple radios to listen too. These were made with materials that they could get their hands on and were small enough to carry around in a big pocket. You can modify this design if you want to set it up so that itâ€™s tuneable too! Subscribe Link
Earphone Update: A bunch of folks in the comments have mentioned that you need to use special earphones. Raymond sent me an email explaining the earphone controversy.
An earphone converts electrical energy to sound waves by vibrating the air. We detect sound by sensing these movements in the air. The difference between the crystal earphone and regular headsets is that the crystal earphone is very sensitive to voltage change where as the regular headphones require current change to make its diaphragm move. Since a crystal radio is not going to produce large amounts of current the crystal earphones are the best match and will produce noise from the microvolts being produce by the antenna- coil combination.”