An electric piano is an electro-mechanical keyboard instrument that resembles an acoustic piano in that it produces sound when keys are pressed, causing small hammers to strike metal strings, metal reeds or wire tines. However, it differs in that instead of using a soundboard to amplify the resulting vibrations, these vibrations are converted into electrical signals by magnetic pickups, which are then sent to an amplifier and a speaker to produce audible sound. Electric pianos were invented in the late 1920s and became increasingly popular because they were much smaller, lighter in weight, and cheaper than grand pianos. They reached the peak of their popularity in the 1950s, after which they began to be replaced by electronic pianos from the 1980s because of the latters' still smaller size and lighter weight as well as their greater versatility, including the ability to emulate a large number of additional instruments in addition to just pianos.