Rotary acoustic horn

A rotary acoustic horn comprising,

• a shaft having an axial input end and an axial output end;
• and
• at least one welding portion comprising an outer weld face, a first opposing end portion and a second opposing end portion;
• wherein the welding portion is positioned between the axial input end and the axial output end of the shaft such that the outer weld face has a diameter that expands and contracts with the application of acoustic energy;
• wherein the welding portion comprises through holes located between the weld face and the shaft and extending substantially along an axial direction of the welding portion from the first opposing end portion to the second opposing end portion, and
• wherein the sections of at least some through holes change long an axial direction of the through holes.