A rib-stiffened sound wave projector plate is disclosed which generates lowrequency sound waves in a fluid medium when energized and flexed. A flexible sound wave projector plate includes at least first and second parallel, major planar surfaces. The first major planar surface includes at least one set of sound wave projector plate ribs, disposed perpendicular to the first major planar surface. Each set of sound wave projector plate ribs includes at least first and second sound wave projector plate rib set members. Each member of the rib sets are offset or spaced laterally from one another by a first predetermined distance, while the first rib member of each rib set is spaced apart a second predetermined distance which is greater than the first distance between the rib set members. Further, each rib set member has a predetermined height and width which may vary from other rib set members in each rib set.