The piano soundboard is constructed with high precision. The convexity, the thickness of the wood, the strings under the soundboard, and the bed of the soundboard are calculated with precision. Each builder follows his own procedures when he builds the soundboard. The differences can be a variable convexity so that the "charge" is more evenly distributed, or that the thickness is equal throughout the board. Others may have a board that is thicker in the center and thinner towards the edges. The position of the chains under the table is highly individual as is the design and shape of the chains. The perimeter, shape of the edge of the board varies greatly from brand to brand.

Soundboard function

When the pianist strikes a key, the hammer is accelerated towards the string and strikes it. When the string is struck, it absorbs most of the hammer's kinetic energy. The string is set in vibration. There is a deformation in the string which propagates towards the bridge and towards the nut, where it will be reflected and return towards the point of percussion. The transverse deviation is indeed very weak. Each time the wave is reflected against the bridge, it loses some of its energy on the soundboard.

The soundboard now functions as a reflective membrane that transfers over and under pressures to the air, which we perceive as the sound of the instrument.

The reason why a soundboard is needed is that the string has a very small contact surface with the air. To obtain a full and "carried" sound from the instrument, the vibration of the string must be transferred to a larger surface, capable of receiving the vibrations, which moves in unison and carries forward the vibrations. The hammer supplies the string with energy. The harder the hammer strikes the string, the stronger and shorter the initial impulse will be. This means that the harder the hammer, the more partials there will be in the sound.

Material properties

Spruce is the most common soundboard material. Sometimes other materials are used: Douglas pine or plywood boards. However, spruce remains the best material. It is light and resistant. The thickness of the soundboard and the way it is bonded to the inner band are very important factors in the vibrational mode of the soundboard itself. The most popular way is to firmly anchor the board along the entire perimeter of the internal band. In a few old instruments, the soundboard can be found, in some places, suspended freely.

Fir is much stronger, or more difficult to bend, along the grain direction than across the grain (that is, perpendicular to the grain than parallel). This can be clearly seen if we try to fold two rectangular boards of the same shape and thickness, one cut with the grain arranged according to the longer side, and one according to the shorter side. The modulus of elasticity is about 25 times higher when we try to bend the board with the grain along the longest side. The lower internal friction of fir is slightly compared to other types of wood. However, internal friction is about 1.3 times higher along the fiber than across it. It can be stated that the internal friction is approximately equal in all directions.