Composite Acoustic Guitar
Can modern computer simulation programs accurately predict the acoustic vibrations of carbon fiber? Well enough to design a carbon fiber guitar that sounds like a conventional wooden acoustic guitar? These are the questions that myself and Stephen Probert (a fellow Mech.E student) set out to answer our senior year at the University of Washington. In short, the answer is "yes". We spent nearly a year on this project, secured faculty support, funding, and corporate sponsorship (materials), and did extensive modeling and testing before actual guitar construction. Stephen's Master's thesis is a thorough, well written summary of the project with many enlightening pictures. My Winter 2006 write-up is a detailed summary of the experimentation and finite element modeling, and my Spring 2006 term paper is an easy summary of the results. We took the time to finish the two guitars nicely and ended up with excellent-playing instruments!
Carbon fiber, abalone, mahogany, and ebony are the dominate materials in the finished guitars. Here, the headstock sporting Grover tuners and a bone nut.
The macassar ebony bridge. The soundboard is unbraced 1/8" rigid foam core with two layers of carbon fiber fabric on each side, done with wet-layup and vacuum bagging.
Inlay at the 12th fret (my initials). The neck is mahogany with an ebony fretboard and dual-action truss rod.
Before any chips flew, the entire guitar was designed (from scratch) and modeled in Solidworks. This was important in doing the computer simulation as well as determining how everything fit together. The tolerance on string height is less than a thousandth of an inch over 28 inches under 150 pounds of force!
Sample computer (FEA) model showing the displacement of the first resonant mode of the guitar top. More more technical info, see the Winter 2005 pdf above.
One of the necks being milled by a 3-axis CNC mill. Almost every shape of the guitar came straight from the CAD model through 2 and 3 axis mills, CNC plasma cut aluminum templates, laser cut inlays, and scale print-outs.
Raw carbon fiber fabric, soon to become part of a soundboard. Doing wet layups by hand can be messy, but with a little practice we were able to get very consistent results.
In the process of laying up one of the upper body sides. Since the guitar is asymmetric, two custom molds were CNC cut and hand finished at great expense of time, but some things are just necessary to do right.
Custom jig for securely gluing the soundboard and back on. Having never built an acoustic guitar before, much of my time was spent in figuring out all these details and making parts to make parts! The neck is attached with a traditional dovetail joint.
Here, the guitar is nearly finished and ready to undergo fretting. After this is a lot of fine tuning and setup of the action, intonation, nut, and saddle for optimum playability.
Further reading:
Carbon Fiber vs. Wood as an Acoustic Guitar Soundboard (Originally written as a term paper, which was subsequently invited to be published in a CMM quarterly special issue)
Composite Acoustic Guitar Project (A write-up on some of the more technical details)
Design, Manufacture and Analysis of a Carbon Fiber Epoxy Composite Acoustic Guitar (Stephen's Thesis for a MS in Mechanical Engineering, University of Washington)