The invention relates to a public address system including one or more loudspeakers, each of which is in particular equipped with a section for reproducing high-frequency sounds, including a wave expansion guide, which receives, at its input sound waves coming from a transducer and having, projecting in a plane, a form opening outwards from its input to its output for distributing, in a solid transmission angle, the sound waves coming from the expansion guide. According to the invention, the expansion guide includes one or more mobile flaps that can be moved by a movement made parallel to the plane, so as to enable the solid transmission angle of the sound waves to be adjusted.