An improved throat (2) for transmitting acoustic energy from a source driver unit (7) to a feeder section (3) of a directivity controlling acoustic horn is disclosed. The throat (2) comprises: a circular throat entrance (2i) connectable to the source driver unit (7); a rectangular throat exit (2e) connectable to or integral with the feeder section (3); and a circular cross-section to rectangular cross-section transition portion (2a) extending between the throat entrance (2i) and the throat exit (2e). The throat (2) is shaped such that its profiles initially diverge from an axis longitudinal to the throat (14) at the same angle in a direction from the throat entrance (2i) towards the throat exit (2e). Such a throat, when fitted in an appropriate acoustic horn with a source driver unit having a taper matching the aforesaid profile angles, provides a smooth transition for sound waves propagating out from the source driver unit into the horn.