One of the best characteristics of a brace for an acoustic guitar top is a high stiffness-to-weight ratio. The less mass the top and braces have, the easier it is for the string’s energy to set it in motion and create sound. At the same time, the top and braces need to be strong enough to withstand the 150 so pounds of string tension without collapsing.

In the Big Red ABG, I used braces with a sandwich of graphite and balsa (at far right in the picture above). This design was very stiff and light, but because I used standard 1/2″ square balsa struts, with the grain running lengthwise, they were prone to splitting top-to-bottom and required quite a bit of reinforcement at the ends. More recently I tried end-grain balsa sandwiched between layers of phenolic laminate. This was light and resistant to splitting, but not quite as stiff as I wanted.

Finally, I came up with a 5-layer sandwich for the braces in the new acoustic bass guitars: Phenolic laminate, carbon fiber tissue, aluminum honeycomb, more carbon tissue, and unidirectional carbon fiber. This combination is very stiff, stable and light. A nice benefit of this design is that the top layer of the sandwich is the top of the instrument itself, so the mass added by the braces is just that of the honeycomb and carbon fiber on the bottom of the sandwich!

Posted by Brian Goode on Monday, July 3rd, 2006 at 7:20 am.