Basics – is related to the sound quality; can be demolished or replaced by shock or being dropped, which will significantly change the sound.
Known in some cultures as a “the soul” or “the spirit” of the instrument, it is located inside the, and its relative position to acting as a support for the upper board, and is a point from which redirected vibrations to the top and back and thereby has a substantial influence on the tone.
The ends of the sound post are cut follow the arc of the boards in this area to contact well in the inner curve of the instrument. The sound post must be chosen in length that prevent to not be too tight or too loose, and the fit should be tight and clean. Since it not glued in place, can be moved in particular with hard shocks or changes in the climate (top and the back of the instrument to expand and contract with the changes in humidity). This can result in the sound post be either too tight or too loose as a result the sound will vary in quality.
If notice a change in sound quality of the instrument over a long period of time (i.e. by full rich tone towards a shallow, dry, raw or difficult to play instrument) may be that the sound post must be corrected. If you hear a rattle inside the instrument, it is possible your sound post has fallen. If this happens, loosen all the strings go to the luthier. This can happen in shock release or replacement of all strings simultaneously. Will only take a few minutes to put it back, but it is important to be done by a professional. It is good to attend to test the instrument and work with a qualified luthier acoustic which make exactly the sound you prefer.