A musical instrument having strings and a soundboard, wherein the soundboard is excited by the strings by a transducer and is associated with differential stiffening mechanism defining at least two zones of the soundboard that present complementary vibratory behaviors. The two zones are separated by a slot extending along a common boundary between the two zones. The transducer extends across the slot so as to be connected to both zones of the soundboard, such that both zones are excited simultaneously when action is taken on one of the strings.