The invention relates to an ultrasound horn comprising a fixing section (1a), a sealing section (1c) and a transfer section (1b) extending therebetween, one or more elongate recesses (3, 4) being formed at least in the transfer section (1b), and said recesses (3, 4) extending in a direction (A) between the fixing section (1a) and the sealing section (1c). Said recesses (3, 4) have a rounding-off encompassing, along the rounding-off, at least a first portion (5a, 7a) with a first radius of curvature, a second portion (5b, 7b) with a second radius of curvature and a third portion (5c, 7c) with a third radius of curvature. The invention also relates to a novel forming of the transfer section (1b) and recesses (9, 10) at the ends of the sealing section (1c).