Influence of ribs on the radiation of a piano soundboard.

Abstract

The presence of ribs attached to the soundboard of a piano influences the transfer of energy from strings to soundboard through the bridge. Measurements and simulations show that the input admittance at the bridge depends on the distance between string end and ribs. A second effect of ribs is related to the periodicity of rib spacing. Simulations of soundboard driving‐point mobility were conducted for three different spacing rules: periodic, almost periodic with small random fluctuations, and random distribution of spacing within a given interval. The results show that aperiodicity reduces the emergence of strong peaks in the mobility spectrum. Finally, measurements and simulations were made on the radiated sound in an anechoic chamber. The primary effect of ribs here is due to the additional stiffness, compared to a flat plate, which reduces the critical frequency and thus increases the frequency range where the radiated sound power is significant. In addition, the presence of ribs influences the directivity of the sound field: strong differences exist in a plane parallel to ribs compared to ribs perpendicular to them. These results also serve as references for comparison with time‐domain simulations of the complete piano including strings, soundboard vibrations, and radiation.