There is an art to getting good acoustic tone from a cigar box guitar. I’m going to give you a few tips on how I do it.
Tip #1: The Dovetail Joint – This is a woodcraft technique which provides a strong & secure joint. The angles of the dove tail will resist twisting under stress, where a straight tenon joint could fail, or a screw could strip. It is typically done with a router. It takes some practice to create a snug press fit joint.
Tip #2: Bracing the box sides. You want to reinforce the box sides and box corners with minimal interference with the soundboard. I make “L-shaped” bracings that taper away from the soundboard and fit securely into the corners.
Tip #3: Finishing the inside of the box. You may have seen soundproofing in the past. The interior surfaces are jagged to break up sound waves. You may have also noted that the acoustics in an empty room with a tile or concrete floor is far superior to a room with carpeting. You want to optimize the acoustic properties of your box by finish sanding the interior of the box, and applying a coat of sealer (shellac) to give it a smooth, hard surface. Yes, you don’t see this in acoustic guitars, but they are typically much larger acoustic chambers. Just try it sometime.
Tip #4: Tone Bracing the underside of the soundboard in the bridge area needs to be light weight, and tapering outward from the bridge. This means you must know where the bridge is going to be located when you start the build. Be sure the bracing is set across the wood grain of the soundboard, and that the grain of the bracing runs horizontal where the soundboard’s quartersawn grain runs vertical. Style of bracing is also important. Fan Bracing for Acoustic plate bridges. Ladder bracing for floating blade bridges.
Tip #5: Tone is in the Box! Cigar boxes are not created equal. To have great sounding acoustics you need wood. Not Masonite, and not plywood either… real wood. The soundboard also needs to be thin. I recommend no thicker than 3/16th of an inch. This is why most of my acoustic builds use the bottom of the box for the soundboard.
Tip #6: Size does matter. The box must be big enough to amplify the sound waves from the bridge. Physics teaches us that lower notes have longer wave forms than high notes. The box needs to have a dimensional length and/or width long enough to allow the sound wave to form. Otherwise, that frequency will be muted.
Well, that’s it for now. I have to get back to the shop to make more sawdust.