A sound post is a small piece of dowel made of well-aged European Spruce. Despite its rather insignificant appearance, a sound post is the soul of a bowed stringed instrument like the violin. Its exact location is critical to ensure perfect sound transmission.
The sound post stands inside the violin connecting the top-plate and back-plate and is located slightly below the right hand bridge foot. It is standing up only under tension, not glued to the inner surfaces of the plates. It therefore has to stand under the correct tension; too loose and it will fall over, too tight and it will damage the plates. Its end-grain surfaces have to fit perfectly to the inner surfaces of the plates of the violin.
The sound post has to be at a certain spot behind the right hand foot which is different in every violin but follows a strict set of rules depending on the build, shape and density of the plates.
If the sound post is moved only a tenth of a millimetre away from that place the whole violin will not sound as beautiful any more.
It takes years and years of experience to be able to put the sound post in the right place, fitting to the inner surfaces, under the right tension at the right spot.
Many inexperienced people have tried to move it themselves or fit new one without the right tools and knowledge and have destroyed the inner surfaces of their valuable and irreplaceable Master violins.
Fitting the sound post:
With a special tool I measure the inner distance between top and back and roughly cut a piece of already prepared spruce dowel to the right length.
The end-grain surfaces I cut with a very sharp carving knife to an angle similar to the arching of the plates.
Then I stick the sound post to the special tool called a sound post setter and carefully insert it into the violin through the f-hole and stand it up in roughly the correct position.
I then look through the little end-pin hole and check how well it is fitting.
In order to be able to see the other side of the sound post I use a little dentist mirror.
This whole procedure is repeated until the sound post fits perfectly in the right spot under the right tension.
After that it can still be moved around to fine tune the instrument.
If the sound post is in the right spot in relation to the violin and to the position of the bridge, the violin will have a beautiful, even, carrying sound and the strings will speak easily when played with the bow.
It truly gives the violin’s sound its soul.