Composite guitars pioneer new level of sound

Internal bracing patterns produce a unique resonance, while RTM'd neck allows faster chording. Low-temperature prepreg accommodates design flexibility and low-cost tooling.

There's nothing like the sweetness of sound from a wood guitar — but the "tonewood" trees or first-growth conifers such as spruce used to produce a guitar's soundboard, and the tropical hardwoods for guitar backs, are being rapidly depleted. Some, like Brazilian rosewood, are now on the endangered species list. And while wood instruments have an unrivaled sound of their own, they play only sour notes when distorted by the effects of heat, humidity, or water absorption. Now Kuau Technology (Maui, Hawaii) has designed and fabricated 12 all-composite models of Rainsong classical, Windsong steel-string acoustic, Stormsong electric, and Powersong acoustic and electric bass guitars — all of which are as sensitive to endangered tonewoods as to musical quality.

To determine guitar shapes and all-important bracing patterns, Decker sought out another collaborator:   Pimentel & Sons (Albuquerque, N.M.,) where Lorenzo Pimentel and his family have been making wood guitars since 1951. Sons Rick and Robert were as skeptical as their father when Decker approached them to discuss the design of an all-composite guitar. Decker relates, "They thought I was a cross between a heretic and a lunatic," though the Pimentels put it another way. "We've established years of craftsmanship in wood," Rick Pimentel says. "We didn't want to make a mass-produced instrument that would not reflect this high level of quality and expertise." When Decker proved serious in his efforts to design a top-of-the-line composite instrument (most Rainsong guitars are customized and in the $3500 to $4500 price range), and Pimentels accepted the challenge.

The first Rainsong prototype was a traditional classical shape, mainly because that's the instrument Decker plays and the Pimentels have been making for years. Initial tests were rudimentary:   Decker sent Lorenzo Pimentel composite soundboards that Pimentel then glued to the body of a wood guitar. These hybrid guitars were tapped and played, so Lorenzo could both hear and "feel" the sound with his well-trained ear. "Describing the sound of a musical instrument is like describing the taste of a fine wine," says Decker. "The attempt is, at best, subjective and a bit poetic, and gets harder the finer the instrument — or the wine."

Established Pimentel shapes and brace designs translated well to achieve the resonance properties for the composite classical and acoustic models. Rick Pimentel explains that bracing factors include thickness or depth of the brace itself and degree of taper in brace ends, which control sound vibration. Pattern and amount of bracing and exact placement in the soundboard are equally important. Pimentel-designed fan and X-shaped bracing patterns are used in Rainsong guitars. Clayton told H-PC that braces are typically composed of unidirectional carbon fiber/epoxy prepreg strips that are 1/2 inch wide by 1/8 inch thick, and laid up in the mold prior to vacuum bag and oven cure. New, original bracing has been designed for the acoustic jazz and electric models.

Decker adds that the lower resin-to-fiber ratio of ACG's prepreg led to orders of magnitude greater resonance, providing optimized sound projection and volume. Clayton states, "We were actually able to design the sound we wanted once we changed from wet layup to this prepreg. It has good tack, which is especially important for conforming to the design of cutaway models, where a major reverse angle can't tolerate any wrinkling under vacuum."

All the principals in the project agree that resonance in the amplified acoustic models reaches a new level of sustain and projection — partly due to the electrical conductivity of composites. And the appearance of the Rainsong composite guitars is unique — minus the traditional guitar bindings and with a slightly rounded seam edge, as well as black or silver plasma-coated nickel/carbon fiber for the ultimate in aesthetics. But does the all-composite guitar reach the sound quality of a wood guitar? Ask the veteran luthiers:   according to Lorenzo Pimentel, "Composites will never sound the same as wood, but can come close." Rick Pimentel adds, "The composite guitar sound is its own, entirely unique. Since we're running out of the tonewoods, composites are the materials pioneering the next level of sound. We'll continue perfecting that sound; it's different from wood, but with a distinct beauty."