Lecture 3:   Amped Up    
Plugged-In: How Electricity Spawned New Instruments

Before any electric instruments could be invented came first the introduction of amplifiers, i.e. devices that could boost electrical signals and feed them to speakers that would turn the juice into sound. The early history of amplified instruments is spread over the 1930's, stretching into the 1940's. Important concept: the sound that we hear comes from a device distinct from the instrument. With the introduction of the electric guitar it was not the vibrating string that moved the air reaching our ears, it was the speaker cone on an amplifier that was pulsing against our ears.

All this was made possible by the principal of magneticinduction, first discovered by Michael Faraday in 1831.