A bracing structure for a soundboard for a musical instrument is disclosed, the bracing structure being a unitary sheet structure having a plurality of elongate semi-tubular elements. A dielectric film, a solid electrolyte layer, and a current-collecting layer are formed in this order on the porous section. The modular blocks are six sided with a detent and fastener mechanism for attaching the block to the gauge bar. The plurality of converting units are configured to convert the at least one amplified signal for obtaining at least one strength value of the at least one amplified signal.