Violin Soundpost Patch

An advanced repair for cracks to the front of a violin in the soundpost area

In this video, we look at some of the steps involved in repairing a crack to the front of a violin in the soundpost area. The full video for the restoration of this violin, on the Masters of Craft channel, can be found by clicking the button below:

Soundpost Crack Causes:

As the wood of the soundpost connects the front and back of the violin, any sudden impacts such as a drop or fall may crack the wood where it connects with the front or back. As the front of an instrument is most commonly made of spruce and the back of maple, a soundpost crack is most common in the front. Being a lighter, lower density wood than maple, spruce is more susceptible to cracking, especially along the grain, the long winter growth.

Another cause of cracking may be a soundpost that is too tightly fitted. This may cause both unnecessary stress to the instrument and make it sound harsh and high tension. A little soundpost tension may be desirable to achieve a punchier, more direct and focused tone, but too much can be dangerous for the instrument.

The passage of time can affect the tension of the soundpost too. As the wood of the violin expands and contracts through the seasons and years, the tension of the soundpost may increase and decrease accordingly. Excess highs and lows of temperature, as well as humidity will affect the instruments balance. Much of this is natural but it’s always a good idea to have a check up with your luthier.

Professional Violin Repair:

A soundpost patch is a fully insured repair performed by a trained luthier. While gluing and studding a soundpost crack without a patch may help temporarily, it is not a guaranteed repair. A violin soundpost will reintroduce tension to the instrument and most likely reopen the crack. Replacing the wood of the crack with a new, expertly fitted internal patch will ensure that the crack will not reopen.

An instrument’s value after a soundpost crack:

As a general rule of thumb, an instrument that has suffered a soundpost crack may be devalued by around 20% if cracked on the front and 50% if cracked on the back.

It is so common for very old instruments to have a soundpost crack though that in our opinion, such a commonality does not devalue the instrument at all, if cracked on the front. An old instrument if cracked in the back will still be devalued by around 50% however.

It is also essential if a crack occurs that this guaranteed repair is made, without which it may be difficult or impossible to sell an instrument. This should be factored into the price of an instrument when buying a violin from a violin shop or dealer.

If you would like a luthier to assess your violin for any soundpost cracks, message us using the button below:

How a violin soundpost patch is made:

As we can see in the photo above, a solid cast is first made of the instrument, to protect it while fitting and enable the perfect amount of pressure to be made whilst gluing it in.

This particular cast is made of dental compound, which is heated in a water bath until soft. When at the correct temperature, the cast is removed and the form of the violin is taken. A wooden backing board is placed behind to facilitate clamping and a layer of clingfilm is used to protect the instrument itself.

When clamped in place, under the soundpost area, it is left to cool and solidify, creating a perfect mould.

Removing the cracked wood:

The thicknesses of the original front are recorded so that they may be replicated exactly with the new patch. If the wood is particularly thin, a possible reason for the crack in the first place, the luthier may replace it with a thicker piece for security.

The cracked wood is removed in a reversed dome shape, with the mould behind protecting it while it gets thinner. The violin front will become less than 1mm thick during this process, to remove as much of the original crack as possible and replace it with new, stronger wood. Starting with a gouge, then moving on to a sharp scraper and finishing with a very fine sandpaper.

Fitting the new soundpost patch:

A spruce patch is prepared as the new piece of wood that will become part of the violin. It is made from fine grain, well seasoned spruce. A luthier may want to replicate the original grain of the instrument also, off setting the grain to one side slightly to give it strength.

The patch is dome shaped and ovular, making sure that there are no hard, straight lines that may crack the wood if a future impact occurs.

Using fine chalk in the newly made hollow, the patch is fitted with the precision of a trained luthier. First using a chisel, then file, sanding stick and scrapers. It is essential that the new patch fits perfectly, as it will become an intrinsic part of the violin, securing it and affecting its tone.

Some luthiers also like to clamp the patch in place, then glue in location studs around its perimeter to ensure it goes back to the same place every time.

Above: Using a sanding stick to finely fit the soundpost patch into place

When fitting perfectly, the patch is trimmed above the height of the front and hide glue is prepared. This strong, long lasting but reversible glue is a fundamental part of musical instrument making and essential in the luthier’s workshop. Applied hot, it will bind the wood together firmly for centuries to come.

Below: The soundpost patch trimmed & glued in with two clamps, with the cast underneath.

The clamps are left on for at least six hours while the glue dries and sets, becoming rock solid. When the clamps are taken off finally, the excess wood is then removed with thumb planes, to flatten the patch and bring it back to the original thicknesses of the violin, checking with a dial calliper.

Above: Trimming the new soundpost patch back with a thumb plane

Below: Checking the thickness of the new patch with a dial calliper

The soundpost patch is now complete, with a new, strong piece of wood reinforcing the violin plate, having removed the crack in the previous old piece. The guaranteed repair is finished and the violin can go on to perform securely for many more years.