As each instrument leaves a workshop, it is adjusted to sound its best at that moment in time. However, a violin is made from many individual parts and several different types of wood. Wood, being a porous material, is sensitive to changes in atmosphere, temperature and especially humidity. As each part of the violin expands or contracts at a different rate, factors like the neck angle or the tightness of the soundpost are affected, which in turn will influence the quality of the sound.
Another cause for an instrument being 'out of adjustment' is the bridge being moved during daily use, either while the player is straightening it or through it being accidentally knocked. Even a small movement of the bridge can have a large impact on the sound and response of an instrument, so often a small adjustment is all that is needed to restore your violin to its former beauty of tone.
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