By David Folland | From the December 2009 issue of Strings
One of the most often asked questions string players pose about their instrument goes something like this: “Why does my violin back have two pieces, and my stand partner’s violin just one?”
In other words, is a one-piece back better than a two-piece back?
The answer can be somewhat complex, but basically, one is not inherently better than the other.
The Two-Piece Process
The majority of violins are made with two-piece backs because they can be cut from a tree only slightly wider than the instrument that will be made from it. Since there are more small trees than big trees, there is a greater selection of small cuts from which to choose the right piece of wood.
To make a two-piece back, the wood is first cut out of the log in a wedge (Ex. 1), like a piece of firewood. This wedge is then cut again down the middle (Ex. 2), opened up like a book, and the thick edges glued together to make a wide plank. The resulting back is “quartered,” meaning the wood grains are perpendicular to the plane of the ribs, which is its strongest and most stable orientation.
It is also “book-matched,” meaning the grain, flames, and consistency of the wood are fairly symmetrical from side to side.
The One-Piece Process
A one-piece, quartered back is cut from a single wedge wide enough for the entire back (Ex. 3). This back has the same vertical grain as a two-piece back, but needs to come from a tree that is more than twice as wide as the instrument that will be made from it. Rare is the tree that is wide enough for a one-piece quartered cello back! One- and two-piece quartered backs cut from very similar wood can be tonally quite similar. However, when the grain orientation is changed from vertical to horizontal, or “slab” cut, there is usually a marked change in tone.
The Sonic Impact
A slab-cut back is flat sawn through the log (Ex. 4), like a board from a lumberyard. A slab back tends to produce a deeper, rounder, less edgy sound. This can work well for violas and cellos, but many great-sounding violins have been made from slab-cut wood as well. However, slab backs are not as stable as quartered backs, and over time usually exhibit more arching deformation, though they continue to function quite well.
What is important is not whether the back is made of one or two pieces, but rather that the wood is good. And it doesn’t hurt if it happens to be drop-dead gorgeous, either.
Q: Why are the plates [top and back]of the violin usually made of two joined pieces? Wouldn’t a one-piece plate be structurally superior? —Conrad Szablewski Flushing, New York
A: There are a number of reasons for using two-piece top and back plates on an instrument. Most are the result of tradition, beauty, and economics.
For the sake of simplification, let’s concern ourselves with the top or table of a violin, which is usually of spruce, a strong, lightweight wood. Its grain reflects how the tree grew. Growth occurs every year in the tree’s outermost layer, just under the bark, expanding the tree’s girth and adding another grain. This annual growth starts in early spring with lush wood characterized by pulpy, air-filled cells, which are light in weight and color. When the tree growth slows to a halt in summer, the cells get smaller and denser, compacted into tough red lines. This cycle of annual growth rings repeats year after year until the tree is harvested. Grain in a violin top will run the length of the plate when cut out of a tree on the quarter and will usually look like pin striping. The harder grain from summer growth will act like joists to make the plate very strong, able to withstand string pressure; yet, because of the softer spring growth in between, the plate remains light and flexible. These two properties are essential to good top wood. (For more about properties of wood, see Understanding Wood by R. Bruce Hoadley [Taunton Press, 1980]).
To get an idea of how different cuts of wood come out of a tree, picture a log the length of a violin top, standing on end like a tall cake. Cut or split a wedge from it. Split the wedgeinto two thinner wedges, and open them like a book at the spine (hence the term “book-matched”). Join and glue those thicker (bark) sides together to make a bigger board, and plane one side flat. The other side of this board looks like a very low-peaked roof: the peak in the center of the plate will be the peak of the arching. This book-matching method explains why tops and backs cut out this way have symmetrical figure radiating from the center joint.
Violins are approximately eight inches wide at the lower bouts, so a log only has to be about five-plus inches to the center of the tree, or about a foot in diameter, to be usable. Smaller trees, which frequently grow in the shade of larger ones and have finer grain as a result, can be well suited to violins. When a tree is big enough (at around 20 inches in diameter), a one-piece quartered violin top or back can be cut out. Such sizes are more rare (more expensive)and are most frequently used as two-piece cello plates. Another way to cut wood from the tree is “on the slab.” Picture the original log, but this time instead of splitting a wedge out, you cut the log into long boards. The first few boards have the round of the tree on the sides, but eventually a board wide enough for the lower bouts comes off. The grain in this cut of wood is more parallel to the arching. Slab tops are very rare, seen only on early Brescian instruments, like those of Gasparo da Salò, or those from lesser members of the Testore family of Milan. Slab backs are less rare and can be very lovely, with a much silkier look to the flame than quartered wood provides. The grain lines in slab wood can run like contour lines on a topographical map. Because they are a little weaker, slab backs are usually left a bit thicker than quartered backs.
The beauty of a one-piece back is undeniable, and the extra cost of the wood adds to the cost of the finished instrument. But the strength of an instrument is unaffected when a two-piece plate is used (and two-piece backs can be equally exciting to look at). Making a center joint is a very difficult thing to do well, but when it is done with precision, traditional hide glue has a wonderful record of holding wood together. If you look at a center joint in the back of a Stradivari violin, you rarely see a glue line—you see only where one piece of wood touches another. In many cases, joined wood planks are actually the strongest option; one big piece of wood is subject to natural internal stresses that want to pull it apart. This sounded like such a simple question, but we haven’t even scratched the surface. A questioner in the not-too-distant future might ask why there aren’t computer-formed carbon fiber–cast instruments made entirely in one piece—but we’ll leave that to the next generation. —contributed by Joseph Grubaugh and Sigrun Seifert
The complete edition of the Care & Repair of Violin or Viola series from Strings magazine gives you a library of video and written instruction that will provide you with extensive knowledge that will help you understand your instrument and, in turn, be a more informed owner and user of stringed instruments and bows.