Here is a shimmed soundboard. The light coloured stripes are the filled cracks. Thin wedges of spruce are cut to size and glued into the cracks to restore the board to its original state as an acoustic unit.. The metal parts are the bridges which transfer the string vibrations to the wood.
A piano with overdamper action viewed from above. The (over)dampers cut off the view of the hammers.
These pianos cannot be recommended, for even where the damping quality is adequate, the tone of the piano fails to meet today's standards.
Old keyboard felts
Here you can see cracks in the soundboard.
These cracks develop over a period of time through humidity and temperature fluctuation; they weaken the soundboard's ability to transfer the vibrations thus reducing the tone quality.