A well-designed and properly-crafted bridge is critical to the tone production of the instrument. The bridge is the link between the strings' energy and the soundboard. How that energy is transferred, as well as where the energy is transferred to on the soundboard are vital.

The most widely acclaimed bridge is the one developed for the violins made by Antonio Stradivari. Prior to Stradivari's designs, the violin bridge was an elaborately carved part that showed little consideration for how the strings' energy would make its way to the soundboard. Stradivari designed a bridge in which none of the strings had a direct route to the soundboard. Instead, the energy would be attenuated through the waist of the bridge and distributed evenly to the soundboard via the two bridge feet. Even the two center strings had their path disrupted by the bridge's kidney-shape opening in the center of the bridge. In this design, the bass foot rested on the soundboard directly over the bass bar, and the treble foot rested on the soundboard near to, but not directly over, the soundpost.

 The mandolin bridges developed by Gibson went through a few design stages. The earliest bridge was a thin one-footed bridge. It was followed by another one-footed bridge that was made taller to accommodate the change to a 4° neck angle. In 1909, George Laurian, one of Gibson's engineers, designed a bridge with interchangeable string contacts so that the musician could select the intonation that best suited his or her strings and instrument setup. In 1920, Ted McHugh (the designer of Gibson's truss rod) and Lewis Williams (one of the original investors in Gibson and later became Loar's partner in Acousti-Lectric after they left Gibson) filed for a patent for a two-footed adjustable bridge. Loar signed the application as a witness and the patent was issued in January, 1921. This bridge (see drawing below) featured a long single foot and an aluminum saddle that was supported by two posts, and thumb wheels that provided for height adjustment. (For a photo of this bridge on Loar's workbench, visit our website). The aluminum saddle proved to be too rigid, and the bridge design was quickly changed to feature an ebony saddle with the center section of the foot removed so that, in essence, the bridge had two feet, one resting over each of the tone bars.

 

This bridge design can be improved, and testing new bridge designs might be something you want to play with. Making a bridge is not really difficult, and you can build a test bridge and put it on your instrument without disturbing any of the instrument's physical attributes.      

We have played with many bridge designs and have a few on the drawing board at the moment. Among the few design changes we have made to the bridges we manufacture is a relocation of the two adjusting posts - moving them outward 1/16" to position the posts closer to the tone bars. And, there's another important change we have made - correct intonation points. Most other folks who make bridges today have copied the intonation notches of the early Gibson mandolin bridges, and they fail to realize that the strings made in the early 1900's had a very different alloy and composition than the strings made today. The elasticity was different from modern-day wire, and intonation issues the wire presented were a bit different from those of today's strings. Our intonation notches are designed to correct for today's mandolin wire, and you might want to consider copying the location of our notches if you make any test bridges.

Carbon fiber is well known for its incredible strength, light weight, and stiffness. Many luthiers use it instead of steel truss rods in the necks of the instruments they build, and there has been a lot of controversy about the merits of carbon fiber instead of steel truss rods in musical instrument necks.

While carbon fiber is stiff, it can bend. And, if it is not installed properly, it can take a set in the neck wood. Lastly, while carbon fiber is light, necks should have sufficient mass to prevent damping and promote sustain. The upshot of any or all of these issues is that carbon fiber, in my opinion, has its place; and for me, it is not in mandolin necks. My preference is an adjustable steel truss rod to counter the force of the 160+/- pounds of string load that wants to bend the neck.

However, there are times when carbon fiber rods can play a vital role. We recently had an A4 mandolin in for repair. The neck was cracked through the heel, and the neck wood cracked in the dovetail joint (that is, the dovetail itself didn't come apart, but the neck wood just in from the dovetail had cracked). The breakage was unusual and it called for an equally unusual repair.

The fretboard was removed, and the neck was pulled free of the body. Once the neck was glued back (with hide glue), Ken and I were concerned about the structural integrity of the joint since we didn't really have a positive locking connection. To improve the connection, we carefully fitted a wood spacer between the end of the neck and the headblock, and when that was set, we routed a narrow channel from the neck to the headblock into which we used epoxy and installed a carbon fiber rod 3-1/2˝ long and 1/2˝ high.