Abstract: Equaliser (4) or phase plug, for electro-acoustic transducers (1), having at least a central hole (40), and or a first series of openings (41), or slots, in the from of concentric rings, coaxial to an axis (4a) of symmetry of the phase plug (4). Said phase plug is characterised in that it has at least a second series of radial slots (42) positioned externally to said hole (40) or to said first series of slots (41). In the phase plug (4) has a third series of radial slots (43) interposed between said first and second series (41;42).