A simple technique for maintaining the beamwidth of a transducer constant over a very wide frequency range (over N octaves) is described. An acoustical end-fire line array of five weighted sensors is used to produce a radiation pattern, without side lobes, at frequency F 1. A half-scale model is implemented to give the same directivity pattern at frequency 2 F 1. Two compensation filters, whose frequency responses are derived by imposing the constant beamwidth constraints, are used in the respective array outputs, to produce a constant beamwidth, without side lobes, over the octave. The design process is repeated N times, to obtain an acoustical array without side lobes and with constant beam shape over N octaves.