Resonator &Amp; Lap Steel Guitars
From 1927 to 1941, The National Instrument Company came out with one of the most distinctive line of musical instruments ever. Headed by John Dopyera, who later founded the Dobro Company as well, they invented and manufactured stringed instruments with spun aluminum cones, similar to speakers, under the bridge, acting as an acoustic resonator. The top line guitars, tricones, had three cones, and were made of silver; the cheaper models had one cone and were made of steel. They made both Spanish style and Hawaiian (lap style) guitars, tenor guitars, mandolins and ukuleles. National guitars are quite popular among blues and slide guitarists for their unique tone, but they can be used for many other styles of music.
Hawaiian music was all the rage on the mainland US during the early 20th century, and many manufacturers including National, Weissenborn, Kona and others made Hawaiian style guitars. These guitars are played lying flat in the lap, using a steel bar to fret the notes, thus sometimes called lap steel guitars. The original standard tuning was in A, either low bass, EAEAC#E or high bass, AC#EAC#E. Most people tend to tune them lower now, and a wide array of open tunings are used.