By the late 1800's advances in electrical theory were providing the foundation for the development of many new technologies including electric motors, trollies, and lights. In large urban areas like New York City electric street lamps were starting to appear, and even home lighting was beggining to be available to those wealthy enough to afford it. One of the many other tasks inventors were seeking to accomplish was that of using electricity to make stringed instruments louder.
By the 1920's and 1930's the advent of Big Band and Swing music like that of Benny Goodman and Glen Miller, along with the increasing popularity of public dances led to a clear need for louder guitars, even the introduction of steel strings was designed to increase the volume of the acoustic guitar. Simultaneously a new style of slide guitar playing began to appear in Country-Blues music utilizing a Hawaiian style guitar. The Hawaiian guitar is the forerunner of the modern pedal steel guitar, it is a flat instrument with between 6 and 8 strings that is played while resting on the players lap, unfortunately these flat guitars had little resonance and could barely be heard when playing with other instruments.
During this time two Los Angeles musicians George Beauchamp and John Dopyera began trying to find ways of creating louder guitars. After some failures Dopyera came up with the idea of using aluminum disks in conjunction with a metal body. They found that this made a guitar that was 3 to 5 times louder than a traditional acoustic guitar and had a sound that lent itself idealy to slide guitar style playing. In 1927 Beauchamp and Dopyra formed National String Instrument Co., which patented the new resonator design. The resonator made by National quickly became popular among Country and Blues slide guitar players but due to internal problems between Beauchamp and Dopyeara in 1930 Beauchamp was fired from the National String Instrument Company. At a later date the company was sold and Dopyera began to produce the resonator under the name of the new company he founded with his brother "Dobro".