Your First Crystal Radio (How to) or building a crystal radio out of household items.
The most difficult part of building a crystal radio is building an efficient earphone that can convert the tiny electrical signals into tiny sounds that our ears can hear. Our first radio used a telephone handset for an earphone, and that works quite well. But another type of earphone is available that fits in the ear so you don’t have to hold it. It is also more sensitive than the telephone handset.
In order to convert very faint electrical signals into sound, we need a very sensitive earphone. The kind of earphones used in transistor radios or CD players will not do. Those are meant to be driven by a signal loud enough to drive a speaker, and are not sensitive at all.