Violin Explained

The Sound Post

From Left to Right. Sound Posts that you can expect to find in poorly worked on instruments and factory rush rush editions. The one on the far right is what a sound post should look like.

The above ‘borrowed’ image shows how the relationship between the sound post, bass bar and bridge work.

The sound post is a ‘dowel’ of quarter sawn spruce that is positioned inside all violin family instruments. It is known in French as l’âme (the soul) because it is the singular part that transfers and regulates the sound – the graphic equaliser. The central point between the Bridge, top and back that determines how, depending on its position and contact inside the instrument, it sounds and how well it responds.

Once positioned in the relatively correct place, it can be moved within fractions of a millimetre or millimetres to alter and regulate the sound and response of the instrument. The smallest movement of the sound post can have a major influence on how well or poorly the instrument sounds. Even a Stradivari violin can sound harsh and wild if the sound post is too tight, thin, not making correct contact or completely dead if too loose or far from the bridge.

The relative position of the sound post determines the intensity of the sound, the balance between the upper and lower registers and how well the harmonics of the instrument resonates in phased vibrational modes.

Of course, there are other influences from the construction of the instrument that determine what sound is produced and where the sweet spot of the sound is. One example of this is often experienced when you decide to use a different set of strings and find that the fantastic reviews are seemingly rubbish! Not so fast, in this case it is just the response of the instrument with different strings that needs regulating so that the two relatives ‘meet’ in a position that causes a pleasing resonance.

It is ‘loosely’ held in place between the top and back plates of the instrument, about the diameter of itself mid back of the bridge treble side foot. It is supposed to be cut exactly the shape of the instrument’s inner arch slope so that the contact area of each end is a flush fit. A general rule of thumb, if the fit of the sound post is snug it will produce a clean and pleasing sound. If it does not fit well on either end or both it will likely produce an intensity that is not pleasing to listen to because the ‘concentrated’ transfer of sound amplifies too much for the plates to handle it. The same principle as being stepped on with a regular shoe heel or a stiletto, the stiletto concentrates the load.

Additionally, if the sound post is cut with too much angle on either end there is a chance that it may cause a sound post crack because of the pressure on the post edge causes it to skewer through the quarter sawn grain of the plates. This is detrimental to the instrument and particularly expensive to repair – depending on the type of instrument and repair method.

Best idea is a well a cut post in the right and first place.

This means visiting a Luthier when you walk out of cash converters or most music shops – right after you bought it.

An interesting example of someone who needed to get the sound in without a sound post setter … problems are that the wire is still attached and the top of the post is poorly cut! The dark edge on the right is the contact area.

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