Photo of an American family in the 1920s listening to a crystal radio. From a 1922 advertisement for Freed-Eisemann radios in Radio World magazine. The small radio is on the table. Crystal sets work off the power received from radio waves, so they are not strong enough to power loudspeakers. Therefore the family members each wear earphones, the mother and father sharing a pair. Although this is obviously a professionally posed, promotional photo, it captures the excitement of the public at the first radio broadcasts, which were beginning about this time. Crystal sets like this were the most widely used type of radio until the 1920s, when they were slowly replaced by vacuum tube radios.