Input impedance and sound radiation of the piano sound board
Klaus Wogram · The Journal of the Acoustical Society of America · 1987
The soundboard of the piano acts as the signal converter from the string vibration to the airborne sound. The type of mounting of the soundboard on the back, as well as the ribs, influences both the sound radiation and the input impedance that acts as a load for the strings as vibration generators. Furthermore, the iron plate affects the effectiveness of the soundboard. Extensive measurements have shown that mass loading by the ribs is in general too large to compensate for the unisotropism in its modulus of elasticity. This causes an additional damping and sometimes an increase of the decay rate of the piano sound.