For the simulation of sound pressure, the soundboard is imbedded in a case with perfectly reflecting surfaces. In some situations, a lid and a bottom plate are added in order to investigate their influence on the resulting sound. The figures below show the meshes used for the five modeled pianos, with identical scale for comparison. The strings, hammers and keyboard are removed, for clarity. The sound pressure is generated by considering the continuity of the normal velocity between the vibrating soundboard and the acoustic velocity.