A resonator guitar or resophonic guitar is an acoustic guitar that produces sound by conducting string vibrations through the bridge to one or more spun metal cones (resonators), instead of to the guitar's sounding board (top). Resonator guitars were originally designed to be louder than regular acoustic guitars, which were overwhelmed by horns and percussion instruments in dance orchestras. They became prized for their distinctive tone, and found life with bluegrass music and the blues well after electric amplification solved the problem of inadequate volume.
Resonator guitars are of two styles:
Square-necked guitars played in lap steel guitar style
Round-necked guitars played in conventional guitar style or steel guitar style
There are three main resonator designs:
The tricone, with three metal cones, designed by the first National company
The single-cone "biscuit" design of other National instruments
The single inverted-cone design (also known as a spider bridge) of Dobro brand instruments and instruments that copy the Dobro design
Many variations of all these styles and designs have been produced under many brand names. The body of a resonator guitar may be made of wood, metal, or occasionally other materials. Typically there are two main sound holes, positioned on either side of the fingerboard extension. In the case of single-cone models, the sound holes are either both circular or both f-shaped, and symmetrical. The older tricone design has irregularly shaped sound holes. Cutaway body styles may truncate or omit the lower f-hole.
History
National tricone
John Dopyera, responding to a request by the steel guitar player George Beauchamp, developed the resonator guitar to produce an instrument that could produce sufficient volume to compete with brass and reed instruments. Dopyera experimented with configurations of up to four resonator cones and with cones composed of several different metals.
In 1927, Dopyera and Beauchamp formed the National String Instrument Corporation to manufacture resonator guitars under the brand name "National". The first models were metal-bodied, and featured three conical aluminum resonators joined by a T-shaped aluminum bar that supported the bridge—a system called the tricone. National originally produced wooden-bodied Tricone models at their factory in Los Angeles, California. They called these models the Triolian, but made only 12 of them. They changed the body meant for tricones to single-cone models, but kept the name.
Dobro
In 1928, Dopyera left National to form the Dobro Manufacturing Company with his brothers Rudy, Emile, Robert, and Louis, "Dobro" being a contraction of Dopyera Brothers' and also meaning "good" in their native Slovak language. Dobro released a competing resonator guitar with a single resonator with its concave surface uppermost, often described as bowl-shaped, under a distinctive circular perforated metal cover plate with the bridge at its center resting on an eight-legged aluminum spider. This system was cheaper to produce, and produced more volume than National's tricone.
Over time, the word "dobro" has become a genericized trademark used to refer to any resonator guitar.
National biscuit
National countered the Dobro with its own single resonator model, which Dopyera had designed before he left the company. They also continued to produce the tricone design, which many players preferred for its tone. Both National single and tricone resonators remained conical, with their convex surfaces uppermost. Single resonator models used a wooden biscuit at the cone apex to support the bridge. At this point, both companies sourced many components from Adolph Rickenbacker, including the aluminum resonators.
National Dobro, Hound Dog, and Gibson
After much legal action, the Dopyera brothers gained control of both National and Dobro in 1932, and subsequently merged them into the "National Dobro Corporation". However, they ceased all resonator guitars production following the U.S. entry into World War II in 1941.
Emile Dopyera (also known as Ed Dopera) manufactured Dobros from 1959, before selling the company and trademark to Semie Moseley, who merged it with his Mosrite guitar company and manufactured Dobros for a time.
In 1967, Rudy and Emile Dopyera formed the Original Musical Instrument Company (OMI) to manufacture resonator guitars, first branded Hound Dog. In 1970 they again acquired the Dobro trademark, Mosrite having gone into temporary liquidation.