By James N. McKean | From the March/April 2020 issue of Strings Magazine

Sometimes your best friend is your worst enemy—and it’s always someone you can’t live without. When it comes to your violin, it’s the soundpost: the indispensable heart and soul of your instrument’s sound and response. Since it can be adjusted to meet your own particular needs and taste, it’s your best friend. But it can also break your heart.

A dowel of spruce wedged between the top and the back, the soundpost is set just inside the treble foot of the bridge, and slightly back of it, toward the tailpiece. That off-center position is what makes it acoustically so important: By not being directly under the bridge, it allows a delay of the vibrations from the top to the back. The two plates are connected, and yet independent, making a vital contribution to the complexity of the overtones. It’s a delicate balance—the top and back have to be strong enough to withstand immense pressure and constant movement, and yet flexible enough to vibrate freely. That’s easy enough to do for an experienced violin maker, and the results can be astonishingly long-lived—there are violins being played today made over four hundred years ago with no damage from the soundpost.

But even the best balance can be upset. No matter how careful you are, accidents do happen; you slip on the ice and the case goes flying, or you land on it. And that’s when your best friend can, in a second, turn into your worst enemy. The angled ends of the soundpost have to match the inside arching perfectly, and the edges left sharp to ensure the best and most complete contact, and to keep it from slipping. Almost without exception, a soundpost crack is the result of a sharp jolt, when that sharp-edged, hard dowel turns from a piston into a spike, cracking the wood it rests against.

If your instrument does happen to get a soundpost crack, there’s no way around it: This is as serious as it gets. Aside from the intrusive repair, there will be significant depreciation. “It’s usually ten to 15 percent of the total value for a soundpost crack in the top, but for a crack in the back, it’s 40 to 50 percent,” says Rob Mayes, director of sales at Carriage House Violins in Upper Newton Falls, Massachusetts.

A back crack is so much more problematic than a top crack—which is why it accounts for a much higher rate of depreciation. Aside from the fact that the maple is twice as thick in the soundpost area, necessitating that much larger a patch, there is a greater chance of the crack reopening. Think of the way the back moves: It acts as a trampoline, with the soundpost constantly pushing it outward as it responds to the movement of the bridge. Also, maple is fiendishly difficult to retouch, and that area of the back is highly exposed and subject to wear.


The depreciation is even greater on contemporary instruments, since a major crack greatly reduces their salability. It’s perfectly understandable: Why would someone buy an instrument with major damage, no matter how well repaired, when they can just go directly to the maker and get a pristine one? The standard practice is to replace the broken part (a time-honored custom, by the way; I know a Stradivari violin with a top made 20 years after the rest of the instrument, and there is a famous Joseph Filius Andrea Guarneri cello with a top by Guadagnini). But then the entire instrument has to be revarnished to match the new part with the rest, and the whole process takes many months before the instrument is ready to be put back in service.

So as substantial as the cost of the repair will be, it’s easily dwarfed by the loss of value. Be sure to get written statements of both from your repair shop to submit with your insurance claim.

The reason a soundpost patch is such a cause of concern is that while the crack looks like just a tiny scratch, it’s in the most structurally stressed part of the instrument, subject to constant pressure and movement. Just gluing it won’t do the trick, even with reinforcing studs on the inside. The only remedy is a patch—thinning down the original wood and replacing it.

The repair itself requires a high level of expertise and experience. Just taking the top off is a risky prospect, one that requires hours of painstakingly slow effort to loosen the plate without causing any additional cracks or damage to the edges. A plaster cast of the top is poured, and any distortions to the arch in the damaged area corrected. Once the crack is glued and the top securely clamped into the plaster counterpart, the area for the patch is thinned down. Only a few tenths of a millimeter of the original spruce are left over the crack itself, to ensure that it doesn’t reopen over time. To match the flexibility of the rest of the top or back, and to prevent any ancillary cracks from developing, the patch has to be gradually feathered in with the original wood. Even though the original crack in a violin top might be a ghost line only a centimeter long, the resulting patch will at a minimum be two and a half by three and a half centimeters, and even larger on the back.

Fitting a patch properly can easily take a full day. Using chalk on the prepared area as a guide, the repairperson minutely shapes the patch with a knife and steel scraper until the new piece is entirely and evenly white from the chalk. Gluing the patch in is an art unto itself. Due to its unsurpassed bonding and invisibility, hot hide glue is still the only adhesive used in violin making or repair. But its proper use, particularly in repairs, requires as much skill and expertise as the actual wood work. If left too thin, the glue can cause the grain of the top to reverse and cloud the varnish; but used too thick, it will gum up and prevent a perfect bonding of the new wood with the old. And it begins to cool almost immediately, so there are only seconds to apply it and clamp the patch in place before it begins to set.

Hide glue takes 24 hours to set and dry properly. After the patch is unclamped, the new wood is very slowly and carefully thinned down to blend with the original. And while the repairperson uses a dial micrometer, graduated in tenths of a millimeter, he or she is guided as much by feel as by the measurements.

How will a patch affect the sound? That’s impossible to know. It varies with every instrument. The wood has been chosen to match the original, and it’s been properly thicknessed to make it blend as well as possible. But still, the patched area is now a sandwich of two pieces of wood, with glue in between. That will inevitably affect the way it vibrates. But restoring the structural integrity of the plate is the driving factor; the resulting sound, good or bad, matters little if the repair doesn’t hold up.

The good news is that all it takes to avoid being your own worst enemy is to be careful. Preventing a soundpost crack (or any damage, for that matter) is pretty simple. Get a set up done by a top professional and keep your instrument in a safe place (the safest being, of course, the case), and you won’t have anything to worry about.