Abstract: The invention relates to multifrequency acoustic transducers exhibiting a wide band around each resonant frequency. It consists in inserting between a .lambda./2 active emitter plate (201) and the soft reflector (203) which supports it a rear plate (202) resonating in .lambda./4 mode and in placing on this active plate two marcher plates (204, 205) whose impedances are designed so as to best match the two frequencies obtained by inserting this rear plate. Thicknesses of these marcher plates are optimized with the aid of a model of for example Mason type starting from a value close to .lambda./4 for the frequency to be matched. It makes is possible to construct sonar transducers which operate equally well in detection mode and in classification mode.