As the acoustic guitar became popular in the early 20th century, players needed ways to increase the volume of their instruments so they could be heard when playing with other musicians in large performance spaces. In the mid-1920s, John Dopyera developed an amplifying system, which he used when he founded the National String Instrument Corporation in August 1926 with his brothers Rudy, Robert, Louis, and Emil. Their company would use Dopyera's system to produce “ampliphonic” or “self-amplifying” guitars, known today as resonator guitars. John received a patent for his design on December 31, 1929.
More-advanced designs soon followed, including one which utilized a single aluminum cone to turn the entire guitar into a speaker cabinet. The guitar strings sat on a thin wooden saddle (or “biscuit”) at the peak of the volcano-like aluminum cone. The biscuit transferred the vibrations of the strings to the speaker cone, which would then resonate, thus amplifying the sound.
John, however, did not think that this single-cone design was well-suited for guitars, since they were so much larger than ukuleles. In frustration, he resigned from National in February 1929 to found Dobro Manufacturing; he derived the name “Dobro” from the first letters of Dopyera Brothers. Dobro modified National’s biscuit design by flipping the cone upside-down and connecting the broad base to the strings with a four- or eight-armed “spider”; unlike the biscuit, the spider conducted the vibrations from the strings directly to the edges of the speaker cone, allowing the cone to vibrate freely.
In addition to the cones, Dobro bodies featured sound holes between the resonator and the neck; in every model except Model 35, which featured segmented F-holes, these sound holes were circular and resembled the portholes of a ship. Because of its overall design, Dobro resonator guitars had longer sustain than single-cone Nationals of the same period.
In fact, the sound of these vintage Dobro guitars much more closely resembled that of the tri-cone or tri-plate National resonators, which, as their name suggests, had three resonator cones, rather than just one. Each resonator cone was six inches across, and the three were arranged in a triangle with two on the bass side and one on the treble side of the body. The three peaks of the cones were connected with a T-shaped bridge topped with a wooden saddle, which allowed all three cones to vibrate in unison, thus amplifying the sound.
As with nearly all resonator guitar designs, these cones were hidden under a sound plate, which were sometimes engraved for artistic effect. Because the vibrations had to travel farther from the bridge to three cones than in single-cone designs, tri-cone guitars were not as loud as single-cone guitars, but they boasted longer sustain and a sweeter tone.
Dobro and National merged in 1935 to form National-Dobro, but by the late 1930s resonator guitars had become less popular, as electric archtops and steel lap guitars became more accepted. National-Dobro made its last resonator guitars in 1940 0r '41. The company continued to sell a few models into 1942, when National-Dobro reorganized as Valco under Vic Smith, Al Frost, and Louis Dopyera...
Today, collectors can find resonator guitars under a variety of brand names besides National, Dobro, and National-Dobro. For example, Dobro built instruments which other distributors like Ward, for Montgomery Ward, sold under their own brands. In 1932, Dobro granted a Chicago-based company named Regal a license to manufacture guitars with a Dobro resonator, and in 1966 Mosrite purchased Dobro and began to produce resonator guitars under the brand Replica 66.
Dobro and National themselves produced a wide array of models and styles, but unlike Martins and Fenders, vintage Dobro guitars are a headache to date with much accuracy. For many years, Dobro model numbers corresponded to prices in the Dobro catalog. As a result, the same guitar could be listed under different model numbers in different years, and multiple designs could be listed under the same model.
Model 45, for example, simply meant that the guitar cost $45. By far the most collectible Dobro, however, is Model 206, only three of which are known to exist today. The instrument's design featured gold-plated and engraved hardware, with a gold sparkle in the center of the body. Most Dobro models were more modest, especially with the onset of the Great Depression.
National manufactured a variety of models in both the single-cone and tri-cone styles. Some of these models featured wood bodies, while others were metal with nickel-plating. These nickel-plated National guitars are extremely collectible for both their excellent sound and their dazzling look—those with round necks allowed different techniques than those with square necks, which are most desirable.
Single-cone National models included the Triolian, Duolian, Style O, and Style N; tri-cone models included Styles 1, 2, 3, and 4. Style 1 was simpler, while Styles 2, 3, and 4 featured intricate engravings and decoration. Style 4, for example, boasted Art Deco-style geometric shapes, surrounded by a chrysanthemum design credited to George Beauchamp, one of the original incorporators of National in 1928. Players today differ over whether they prefer the sharper, louder sound of the single-cone models or the softer, sweeter tone of the tri-cone guitars.
In contrast with Dobro guitars, Nationals have serial numbers that can be easily tied to a year of production. These numbers are generally found either on top of the headstock, on the body by the end of the tailpiece, or on the back of the bridge.
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Pharis and Jason Romero [Acoustic Guitar]HispanicBusiness.com, December 2nd
On top of their ambitious performing and recording regimen they have handcrafted scores of stunning instruments-mostly banjos in a variety of styles and appointments-as well as resophonic guitars and ukuleles. Waiting time for instruments from the J...Read more
A blues man comes home to AshlandThe Independent, November 30th
When he performs by himself, Wills tends to rely upon a pair of guitars including an unusual fiberglass-body six-string resonator he's been working with for years. “It was made by Val-Pro for National or Supro of Kay of Harmony. Mine has a National tag...Read more
Entertainment listings, Nov. 28 to Dec. 4, 2013Champaign/Urbana News-Gazette, November 28th
An American country blues musician, Parr plays a National resonator guitar, a fretless open-back banjo and a 12-string guitar in the Piedmont blues style. Seats $12; groups of six or more, $10. 733-0330. Future highlights. UI Jazz Saxophone Ensemble...Read more
Lincoln Durham draws fans in with old, soulful soundHouston Chronicle, November 26th
He took an electric detour through rock 'n' roll before finding the sound that suited him: Durham bangs on cheap, old guitars, the kind Sears sold in the middle of the 20th century, as well as a resonator guitar and some homemade instruments. Durham...Read more
Jim PharisOffBeat Magazine, November 26th
Lafayette's Jim Pharis' debut album consists of seven originals and two covers, all adeptly finger picked on a steel-body resonator guitar. Overall, the disc has a live feel, as if this took place on a Saturday morning in a subdued coffee shop. Pharis...Read more
Scenic City Roots---Lou WampWDEF News 12, November 19th
Is it bluegrass, yep---but the Wamp band also plays jazz, country, swing, contemporary and just about any other genre that can be adapted to fiddle, banjo, bass...and of course, resonator guitar. They play 40 to 50 gigs a year. Now---about that name?...Read more
Bottom Feeder: My Steampunk GuitarPremier Guitar, November 17th
This recycled speaker frame visually suggests a mutant resonator guitar that's powered by, yes, steam. See the copper plumbing? I like it as a curio piece (as if none of my other guitars already fit that description). I have it tuned to E–B–E, or root...Read more
The Local Pick: Amy Ladd & Friends mark 10 years together, 5 at churchRichmond Times Dispatch, November 13th
Amy performs lead and harmony vocals; Preston, bass and vocals; Audrey, rhythm guitar and vocals; Wingfield, resonator guitar, Dobro and vocals; and Litton, mandolin, guitar and vocals. “Our music is a cross between classic country, traditional...Read more