Considerations for Selecting a Resonator Guitar
The body of a resonator guitar functions like the cabinet used to house an audio speaker. Cabinets are usually heavy and their construction is very sturdy. This forces the sound out of the speaker cone, instead of losing signal due to vibration and the sound energy being absorbed by the cabinet material itself.
Steel - Steel is very hard. They tend to produce a very bright, crisp, sharp tone.
Brass - Brass is softer than steel and may absorb some tone, but usually they are said to have a warmer, softer, blended tone compared to steel.
Wood - Wood being the softest has a delicate tone. Bluegrass Dobro (lap style resonator) players usually prefer wooden bodies. Plywood actually makes for a stronger body than solid hardwood.
Other - Different materials have been used. In an attempt to produce a lighter instrument aluminum has been used, but the softness of the body makes for a muddy tone. Graphite is another experimental material.
A resonator cone (kind of like, a metal pie pan) functions very similiar to a banjo skin. The energy of the strings vibrating move the bridge, that in turn move the cone. The sound comes out of the cone directly like an audio speaker, but also develops inside the body and exits via the soundports in the body's upper bout. A coverplate is used to protect the cone from damage. Cones are manufactured out of aluminum by being spun (superior) or pressed. They are rather delicate.
T Bar Bridge - The Tricone is by far the best model in regards to overall balanced tone and volume. Using a T Bar, three small cones are attached to the bridge. This provides treble, mid range, and bass.
Biscuit Bridge - The single cone is convex like a volcano. On top sits a wooden disk (biscuit). The bridge stands vertically in the middle of disk. This model was very popular with many early Blues players like Son House, Bukka White, and Blind Boy Fuller.
Spider Bridge - John Dopera who invented the resonator guitar had to reinvent his guitar, after he no longer owned the original patents. He inverted the cone to concave like a funnel and placed a spider web type bridge made out of aluminum across the top. This guitar was sold under the name Dobro. Short for Dopera Brothers. Along with the wooden body, this bridge is favored by Bluegrass lap style players, but also it should be noted, the necks are usually different.
There are two types of necks
Round - This is just like the shape found on any standard guitar. 12 frets clear of the body was typical of 1920/1930 guitars. There was no internal support bar (truss rod) installed inside the neck to prevent bowing (neck lifts due to string tension) and it is easier to adjust the intonation (every note plays in tune, all the way up the fingerboard). Later in the late 1930/1940 installing truss rods also allowed for longer necks. Having 14 frets clear of the body allowed for easier access beyond the 12 fret. Also, if tuned to Open D, adding a capo at fret 2, to Open E, there are still 12 frets clear of the body. This cannot be done on a 12 fret without some difficulty.
Square - This neck is rectangular and cannot be played like a standard guitar. It is designed to be played in the lap style. The thicker neck further prevents bowing and allows for more string tension. Traditionally, this instrument was used to play Hawaiian music before it became a popular American country instrument. Initially, John Dopera was actually trying to invent a variation of this lap instrument, so it could be loud enough to compete against standard orchestra instruments.
Strings and Set-Up
Resonator guitars can be played in standard and open tuning. In standard tuning, it it important to hand mute unwanted strings from vibrating causing dissident overtones. This is usually not the situation in open tunings because the open notes are sympathetic to the overall sound.
A good Set - up is essential. String height for slide playing still needs to be low enough to finger notes and chords over the entire length of the fingerboard. The correct string tension allows the slide to ride on the strings without "bottoming out" and hitting the frets. More importantly, it provides the correct downward pressure on the cone. Too little, the cone rattles and has a weak tone. Too tight, crushes and locks up the cone.
String gauge and tuning are related. Usually lower tunings require heavier strings. In general, for below standard tunings like Open D (DADf#ad) and G (DGDgbd), medium gauge "nickel" strings work well. Although, a slightly heavier first string (.016) will provide a better tone. When changing strings, remove one string at a time and tune up. It is not advisable to completely remove all tension from the cone regularly. In this case, slowly tune up the strings symmetrically, so pressure is equally applied to the cone across all the strings. Cones easily "crush in" due to too much pressure.
Republic Guitar Sound Samples ( www.republicguitars.com )
Tricone - http://youtu.be/RmOJ5OYZ1I8
Highway 61 - http://youtu.be/-uMT8KOqKzk
Duolian - http://youtu.be/IWA4dTi2KjU
Parlor - http://youtu.be/s2HjuNpOOek
Tenor - http://youtu.be/nT2BaiVX-38
Tricone and Duolian Duet - http://youtu.be/aT1N4bCq8qQ
Parlor and Highway 61 Duet - http://youtu.be/0s6Jh3hM7Zc
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CD1 Vestapol Tuning (Open D) for 6 string & 3 string cigar box
CD2 Spanish Tuning (Open G) for 6 string
CD3 Comparing Vestapol and Spanish Tuning for 6 string
CD4 Cigar Box Guitar for 3 string
CD5 Cigar Box Guitar for 4 string
CD6 Cigar Box Guitar for 3 string Part 2 (Devil's Tuning Method)