Sound boards having an elongate, approximately trapezoid shape, provided on the front face with a central longitudinal profiled string-carrier member and on the reverse side with a central profiled reinforcing member or beam, and with two side profiled members or sound bars, symmetrically disposed with respect to the reinforcing beam are provided. In such sound boards the cross-section of the reinforcing beam has a central portion with an increased height or thickness and two adjacent, symmetrical side portions or wings having a height or thickness which tapers gradually towards the outside through a concave arcuate profile up to a predetermined minimum value.