An embodiment of a method of designing a grooved reflector comprises selecting two given wavefronts; and designing two surfaces meeting at an edge to form a groove such that the rays of each of the given wavefront become rays of a respective one of the given wavefronts after a reflection at each of the surfaces. According to the invention, the signal of the channel of highest energy is modified in a filter with a transformation function in a first parallel branch and is modified in a second filter with a reverberation function in a second parallel branch, whereupon the modified signals are joined together in a summation unit. Support rod members are provided at the first end plate.