By James N. McKean

The worst piece of playground equipment in days of old was the see-saw. They’re mainly extinct now, and had a predatory look to them: a long pole, balanced in the center, with a seat at each end. You’d see tiny children rising high into the sky—soaring, un-helmeted, ten feet above the asphalt, and then swooping back down. It spelled exhilarating freedom for the child, but pure terror for the watching parent.

For violin makers, it’s still a shame they’re gone. Rather than explaining why the strings go up and down on your instrument, I could just say, “Go watch a couple of kids on a see-saw, and you’ll get the idea.” The long metal pole is the neck and fingerboard; the kids are the weight of the strings tuned up to pitch; and the axle is where the neck is dovetailed into the upper block.

As with the see-saw, your instrument is all about balance. Strings at full pitch exert an enormous amount of pressure, which is increased when you bow them. Most of that pressure goes down through the bridge into the top; the rest is divided between the upper and lower ends, where solid blocks inside the instrument stabilize the top and the back. By themselves, the strings are inaudible; all that glorious sound that you bring forth comes from the amplification caused by the vibration of the wooden box.

That’s where the balance comes in: The wood has to be thick enough to withstand those enormous pressures, but thin enough to vibrate as freely as possible. The body has to be as rigid as it is flexible. It’s quite an engineering task. The trick is to make it as flexible as possible where it will produce the most vibration, but then use the rest to reinforce it. The top is where most of the sound comes from; the back and the ribs provide the extra vibrations that help create the richness of the overtones.

If you look at your instrument from the side, you’ll see that the top rises quickly at each end, but that most of it is flat—particularly the part under the bridge, between the fingerboard and the tailpiece. This isn’t due to settling under pressure. It’s carved that way. That flatness, called the saddle, is crucial to maximizing the movement of the spruce top. As you bow, the top rocks back and forth and moves up and down.

Turn the instrument over and you’ll see that the back arch is an even curve from one end to the other. That’s because it moves completely differently from the top: It’s set in motion by the soundpost, which moves up and down like a plunger under the rocking of the bridge. By themselves, all the parts—the ribs, back, and top—are extremely flexible. You can bend and twist them this way and that. But when the back is glued to the ribs, they suddenly become much less flexible, and when the top is added, this lightweight wooden box becomes very rigid. It’s designed to stabilize the box as much as possible so that the center of the top—the saddle—is free to move.

The delicate balance of your instrument is seen nowhere more than at the ends of the top, where it rises abruptly from the edge to reach the saddle. That part is called the crown, and it’s what for the most part is responsible for your strings going up and down. Because the truth is that the strings themselves aren’t moving at all; it’s the fingerboard. And the amount it can move depends on the shape and strength of the crown. While most of the pressure from the strings is downward, through the bridge, there is almost as much from the compression at each end of the top—at the upper end, the neck setting, and at the lower, the endbutton.

Here’s the trick for a maker: the longer the saddle, the more flexible the top, and thus more sound—in volume and overtones. But the longer you extend the saddle, the steeper you have to make the rise of the crown. And that makes it less stable. It’s endgrain (the wood is cut across a tree’s growth rings), which is weaker, and softens more when the weather turns humid, which is why the strings go high in the hot, wet summer months. So when you have the constant pressure of the pivot of the seesaw—the neck and fingerboard—right against the base of the crown, it has to be as strong as possible.

The truth is that the strings themselves aren’t moving at all; it’s the fingerboard.”

As a maker, I can stabilize that area by making it lower and more gradual. Time is on my side in that regard; arches now are much flatter and lower than they were in the early days of the violin. Almost all makers prior to the end of the 18th century followed the lead of Amati or Stainer, making very high arches with abrupt and steep crowns. Stradivari and a few others were outliers in employing flat arches, which produce a more powerful, bright sound and yield a much greater dynamic range.

The heel of the neck itself is also endgrain, but it’s much thicker, and made of maple—a very dense wood. It’s also sealed at both ends, and firmly held in a dovetail joint. While it might contribute to the movement of the neck, almost all the variation in string height can be traced to the crown of the top. As a maker, I can use the endblocks and thickness graduations to make the crown even more solid.

Some seasonal variation in string height is a part of life, even with the most stable instruments. But it can be minimized. When you’re looking for an instrument, pay close attention to the top arch. A high one, by its nature, can be problematic: Ask the maker or dealer whether this particular instrument needs seasonal bridges. Look at them to see how different the height is: On a cello, a variation of two or three millimeters is to be expected. On most violins, the variation is slight enough that you won’t need seasonal bridges, particularly if the instrument is built on a Stradivari or Guarneri del Gesù model. On an antique instrument, any damage to the top (particularly in the area of the crown, at either end) can affect its stability. Check the schematic drawings of all the repairs.

If your instrument suffers from a lot of neck movement, there’s not much you can do. To eliminate it, you would have to isolate it from all ambient weather—and not many musicians want (or can afford) to live in the hermetically sealed world of a museum. The more constant the conditions, the better, so reduce exposure to humidity as much as possible. You can also ask your repairperson  to make an arch protector. That’s a thin wedge of cardboard specially fitted to go between the top and the fingerboard at the top of the crown. It looks simple, but it’s not: Don’t try making it yourself. It has to be just the right tension, and fit perfectly.