Project Evia : Redesigning the viola
By Joseph Curtin, American Lutherie Journal, Winter 1999
The last half of the twentieth century has seen rapid development in the creation and use of new materials – and in our understanding of violin acoustics. The scarcity of good old stringed instruments is opening up the market for good new ones, and a number of makers and researchers have experimented with non-traditional designs and materials. Such violinmakers as Guy Rabut, Roger Lanne, and Christophe Landon concentrated on aesthetic innovation, while researchers Hutchins & Haines, Charles Besnainou, and Leonard K. John have developed instruments using alternative materials. At the same time, the reluctance of classical musicians to accept non-traditional designs and materials may be slowly giving way. Bowmakers such as Michael Duff and Benoît Rolland, using graphite fiber (also known as carbon fiber) and other synthetics, have achieved considerable commercial success – and made some very good bows.
For my part, after twenty years as a traditional violinmaker, I have started taking time to look for new directions. This article gives an overview of “Project Evia” (‘Evia’ for ‘experimental viola’) — my attempt to redesign, using new materials, the least standardized instrument of the violin family. I decided to build a wooden prototype, which might then be progressively rebuilt using graphite-fiber/wood composites. My hope was to come up with a design that answered to the ergonomic and tonal needs of the professional musician, my own sense of line and form, and the laws of nature. I did not want to worry about the sometimes stifling traditions of classical violinmaking.
Acknowledging that most useful innovation – aesthetic as much as structural – is the result of a great deal of trial and error, I wanted a design that allowed for rapid replacement of parts that didn’t work. This seemed especially important when experimenting with new materials and unfamiliar processes. After many months of sketching ideas, I came up with something I felt was worth building. The overall shape (Photo 1), with its sloping shoulders and simplified corners, looks back to the Gamba, while retaining, at least to my eye, some sense of modern simplicity. The single turn scroll (Photo 2) reads well at a distance and to me has a sense of the architectural about it, rather than the merely decorative. The f-holes were designed to minimize the resistance to air flowing through them. Because much of the damping to the main air resonance occurs at the edges of the f- hole, the shorter overall length of edge produced by this design, along with a slight rounding of the edges, serves to increase the amplitude of this important resonance.
The sloping shoulders give the player’s left hand easy access to the higher positions. This is done without decrease in internal vibrating length; the upper shoulder region of a traditional viola’s back and top is left thick, and further immobilized by the block. Photo 3 shows the linings, which continue over the corner blocks, rather than being set into them as is usually done. I should point out that most of the above elements have shown up in instruments of the past, though not all at once or in quite this arrangement.
Photos 4 & 5 show the neck as it meets the body of the Evia. Traditionally, the neck is mortised into the end block, making it difficult to reset when the neck needs raising or replacing. The Evia’s neck is held in place with a single bolt through the upper block. The simple slide mechanism (Photos 6 & 7) allows quick changes in the overstand (and thus the fingerboard height) to accommodate the seasonal changes a wooden top undergoes, and to allow new tops with different arching heights to be tried. An extended allen key is inserted through the endpin hole in order loosen and tighten the bolt. The bolt itself (Photo 8) passes through the block into a threaded hole in a rod set into the neck stock. The design has the advantage of allowing the top and back to be removed easily. The button is not attached to the back, and the neck only minimally interrupts the top.
If one looks at the traditional viola from the vantage point of several centuries of repair and restoration, the vulnerabilities of its structure become clear. The soundpost, critical to the performance of the instrument, is the often the locus of serious damage. A crack in the soundpost area will devalue the instrument (even when well repaired), and normal wear and tear often results in dents to the inner surface of the top. This makes soundpost adjustment difficult, and predisposes the wood to cracking.
In order to prevent such damage, we (I work with an assistant, Sharon Que, a superb craftsperson and artist in her own right) tried installing a veneer of maple about .25 mm thick in the soundpost area of a violin. It worked so well that we installed one on the wooden top for the Evia, and on all my instruments since then. While developing the idea, I talked with colleagues who had been putting traditional soundpost patches into their new instruments. They found the additional stiffness helped the sound. For those not familiar with the violin world, a soundpost patch is a small oval of spruce set into the top in order to reinforce a repaired crack. If the grain of the patch is rotated a little with respect to that of the top, the top becomes somewhat stiffer across the grain in that area. If you use slightly denser wood, it resists damage better. Because a fair amount of original wood is removed, the operation is non-reversible.
It seemed reasonable, when trying to prevent damage to a new top, to simply glue a veneer on the inner surface. I considered using laminated spruce, parchment, and graphite fiber. In the end I decided on maple. It’s denser and harder than spruce and so the post isn’t likely to dig in. Unlike graphite fiber, it has about the same rates of expansion/contraction as spruce. We make a veneer of quarter cut plain maple and trim it to the oval shape traditionally used for soundpost patches, about 23 mm by 28 mm.
Two methods for installing a soundpost veneer have been used. The first was developed by Sharon Que. Photo 9 shows a small counterform being fitted to the top using Bondo, a fast-hardening compound used for car body repair. A thin layer of tin foil, held to the top with by little spray-on adhesive, stops the Bondo from adhering to the top. The counter-form is simply a piece of half inch thick maple cut to the same oval shape as the veneer. The bottom surface is scoured to hold the Bondo better. The Bondo is mixed and spread onto the counterform, then placed lightly on the top. It spreads easily and makes a very nice cast of that area of the top, drying in about 30 minutes. In Photo 10, the veneer has been taped in place (hide glue already applied) and is ready for clamping (Photo 11). We found that a counter-form was needed only on the inner surface of the top, as long as the other side was adequately padded. Once the glue is dry, the veneer is taken down to a thickness of about .25 mm at the center, feathering down to about .1 at the edges. Photo 12 shows the finished soundpost veneer, the grain of wood rotated slightly with respect to that of the spruce.
We recently adopted a quicker method for installation, using a vacuum bag. Hot glue is applied to the veneer, which is then lightly taped in place (as in Photo 10). The top is put in a thin plastic bag, which is sealed and then evacuated with a vacuum pump. The force of the vacuum produces a very even clamping pressure, with no tendency to distort the top. (More on vacuum clamping later.) Because the pump tends to pull out any moisture along with the air, a clamping time of one hour seems entirely adequate.
I was for a long time reluctant to try soundpost veneers because the soundpost area is such a sensitive one acoustically. But the veneer seems to work extremely well from every point of view: soundpost adjustments become easier, wear is reduced, and the acoustical effects seem if anything beneficial. And because the veneer can easily be removed, the process is completely reversible.
A number of individuals and companies have experimented, in the past two decades, with the use of graphite composites for musical instruments. My own experience in the area comes from working with Charles Besnainou, a research scientist and luthier at the Laboratoire d’Acoutique Musicale in Paris. In 1985, he began building guitars and lutes using wood veneer, graphite fiber, and acrylic foam. He soon teamed up with violinmaker Stephane Vaiedelich to develop composite violin family instruments. Although Besnainou’s methods have been licensed to several large firms intent on mass production, they have the advantage of being well suited to individual craftspersons. The equipment needed can be put together for several thousand dollars, is easy to use, and fits comfortably in small shop.
Besnainou’s system is based on unidirectional graphite fiber, pre-impregnated with epoxy resin. It comes in sheets, with a layer of paper on either side of the graphite, making it relatively safe and easy to handle. It can be cut to shape with ordinary scissors (which are gradually ruined in the process!). The paper is peeled off and the graphite, along with layers of acrylic foam and wood veneer (Photo 13) are set in a plaster mould. This is placed in a vacuum bag and the air drawn out, forcing the materials to conform to the mould with great precision (Photo 14).
The whole assembly is then heated to about 280 Fahrenheit for a number of hours.
The heat is provided, at least on my set-up, by silicon rubber heaters stuck to the underside of a ¾” thick aluminum plate (Photo 15). These heaters came from a science supply catalogue and cost about $70 each. They provide extremely even heat distribution, are easy to mount using silicon cement, and four of them cover the two-foot square plate nicely. Together they give 2000 watts of power, which is about right for a plate that size. (It is important, for proper curing, to be able to bring the mould up to temperature within half an hour.)
The heaters can be controlled by a simple thermostat, though I used an electronic temperature controller and a solid state relay, which does the job more efficiently and accurately (Photo 16).
Photo 17 shows our vacuum pump, a Mercury model rated at five cubic feet per minute. It has an automatic switch which cycles the pump on and off as needed, maintaining the vacuum at a set level (adjustable with a small screw). For a fuller understanding of the scope of vacuum clamping techniques, there are several good books devoted to their use in veneering furniture.
There are people who worry about the aesthetics of graphite fiber. I don’t have any qualms in this regard. It can be covered with wood veneer, or some other material. Left exposed, the black contrasts beautifully with wood when the two are used side by side, as in Photo 18, a wooden lute by Charles Besnainou with a graphite top. Black also ties in with the violin’s frequent accompanist, the piano, and of course the black clothing favored by classical musicians for concert wear.
But why use composites in the first place? There are several advantages, and some disadvantages. Graphite is extremely stable in the face of changing humidity, a quality wood can hardly claim. This create a problem when using it together with wood; the difference in expansion rates, when not accounted for, can create instability. Graphite fiber has an extremely high tensile strength (resistance to stretching), and by sandwiching it over a light core material, stiffness to weight ratios not achievable with spruce (the stiffest wood for its weight) are possible. This can be very beneficial for the power and response of the instrument. Tone quality is greatly influenced by the damping of the materials used. Graphite is less damped than maple or spruce (i.e. it will ring longer when tapped), and so optimal damping must be achieved by combining it with core materials that counterbalance it. This is too complex a matter to go into here, but I believe it represents one of the central challenges to be faced in creating first class bowed string instruments using alternative materials.
I should add that graphite fiber is not cheap. It is difficult to buy in small quantities, and costs more than first class spruce. Furthermore, it has a shelf life – though this can be extended by keeping it in a freezer. But vacuum forming a plate is considerably faster than carving one, and the material’s consistency is attractive beside the unpredictability of wood. Many of the characteristics of composites make them suitable for mass production. This, however, is an area with its own set of problems, and not an area I am much interested in. Project Evia is an ongoing one. The wooden prototype, as expected, sounded much like my other violas. I now have a number of composite backs and tops waiting on my bench for trial. Given the limited amount of time I have to devote to such things, I imagine it will take several years before anything resembling a marketable instrument is developed.
There is a saying among material engineers that something rebuilt using composites is badly designed if it ends up looking the same as the original. Every material creates its own design problems and opportunities. The traditional violin evolved closely around the properties of the woods used. It therefore inevitable, I think, that the adoption of new materials will send instrument design off in new directions. I find this very exciting, and feel fairly sure that successful composite instruments will begin showing up in concert halls within the next decade. I would love to have my label in some of them!