Underneath the soundboard

Underneath the soundboard are a number of ribs which are attached either to give support to the bridges (over which the strings pass), or, in the case of the longer cutoff bar, to control its vibrations.
The rose is firmly attached (to stop it from vibrating) by its four arms to the underneath. The soundboard is planed to a 1/16th" taper at the edges, making it very sensitive to the vibrations produced by the strings acting through the bridges. Correct fitting and treatment of the soundboard is vital for acoustical quality.
Its extreme thinness also makes it vulnerable to large changes in temperature and humidity, which can cause it to bow or crack