An acoustic transformer for transforming sound waves generated by, for example, a round membrane, into a rectangular wave front with reduced interfering resonances is provided in a form of a waveguide with a generally circular entrance and a generally rectangular exit defined by outer walls. The sound waves, arriving from the radiating membrane, are divided geometrically into two flows of sound waves of generally semicircular cross section. Each of the two flows of sound waves is deformed individually into a rectangular shape. Subsequently, the flows of sound waves are brought together once again at an acute angle. The division of the sound flow of circular cross section into two sound flows of semicircular cross section creates two sound flows, which already have a straight side surface. The two sound flows are passed into curved sound guides, which initially have a generally semicircular cross section and then gradually change over into a generally rectangular cross section. A displacement structure which is approximately elliptical in cross section, thickens gradually and, after reaching a maximum, falls off once again, is disposed to protrude inward of the approximately straight and flat wall of each of the sound guides. Each of the displacement structures along with a corresponding one of the outer walls provides a sound channel, which initially is semicircular in cross section, with a bent cross section of uniform thickness and then stretches into a rectangular cross section at an end thereof.