first and second reflectors , having a parabolic concave reflective surface and a conical reflecting surface , respectively , are vertically spaced on co - linear axis . an energy source , such as a loudspeaker mounted atop the frusto - conical second reflector near the apex of the conical reflective surface thereof is at or proximate the focal point of the concave reflective surface of the parabolic reflector . it is desirable for the major diameters of the reflectors to be approximately twice the wave - length of the lowest frequency sound for which the device is applicable . the shapes of the reflective surfaces are established to provide essentially equal path lengths of energy radiated from the source to a wave front to provide coherent omnidirectional energy propagation from the assembly or , in an alternative use of the apparatus , receive radiant energy and focus it on target instead of a loudspeaker at the focal point of the parabolic reflective surface .