Resonator guitars are unique-sounding instruments that use an aluminium, bowl-shaped cone under the bridge to increase the sounds of an acoustic guitar. First built in the 1920s, the resonator guitar has found extensive use in blues, country and bluegrass music. Homemade resonator guitars can be constructed from traditional acoustic guitars using tools found in any woodworking shop.
Begin by carefully removing the back from the guitar. Cut a hole in the guitar face for your sound-well. The sound-well is a drum-like ringed structure placed in the guitar to hold the resonator cone in place and provide structural reinforcement for the cone. The resonator cone should be a concave piece of aluminium about 9 inches across. A thin saucepan can serve as a resonator cone, or you can purchase one from a local guitar shop or online. Resonator cones cost about £52 retail in 2009.
You can either use a pre-made sound-well, or create your own using plywood. The cut on the guitar face should be centred on the bridge and made exactly as large as your cone. Use the cone to trace the hole before cutting. To gain a nice rich sound, cut two sound holes into the face of your guitar, placing them on both sides of the bottom of the fret. The sound holes can be shaped and sized according to your own tastes, but 2 inches is the common size used. Sand the holes smooth when finished cutting. You can use the wood removed to cut a piece of wood sufficient to cover the original sound hole.
To create a plywood sound-well, glue together three pieces of plywood cut in a circle with an inch-wide rim and an interior large enough to hold your resonator cone. Make the top layer slightly wider than the central layer, with the extra width extending outside the centre to provide more surface area for gluing to the guitar front. The bottom layer should be the same width as the central layer, but the inside diameter should be smaller to form a ledge on which the cone can sit.
Glue your sound-well beneath the hole in the face of the guitar and then glue in a back brace for the guitar's rear to provide extra support.
With the removal of the bridge, you'll need to install a tailpiece for anchoring the strings. If using steel strings, you will also need to replace the fingerboard with one designed to take the additional stress. Remove the existing fingerboard and replace with rosewood or another hardwood. Screw a resonator bridge onto the centre of the outside bottom of the resonator cone, and then place the cone into the hole. Cover the hole with a thin metal cover. The cover can be made with any thin sheet metal, but you can use an aluminium lid for convenience. You'll have to cut a space in the cover for your bridge. You should also cut multiple holes in the cover for the sound to escape the body of the instrument; an artistic pattern is generally used for this.
With the cover in place, just string up the instrument, tune it, and it's ready to play.