Abstract: A directional loudspeaker unit for reproducing mid-range audio frequencies, comprising a cone loudspeaker and, disposed forwardly of the surface of the cone of the loudspeaker, a phase plug and a horn, wherein the phase plug and preferably also the horn are arranged co-axially on the axis of the cone, and wherein the phase plug has a central aperture. Preferably the horn has a diffraction slot defined by lateral walls which converge from the entrance (throat) of the horn.

Abstract: A directional loudspeaker unit for reproducing mid-range audio frequencies, comprising a cone loudspeaker and, disposed forwardly of the surface of the cone of the loudspeaker, a phase plug and a horn, wherein the phase plug and preferably also the horn are arranged co-axially on the axis of the cone, and wherein the phase plug has a central aperture. Preferably the horn has a diffraction slot defined by lateral walls which converge from the entrance (throat) of the horn.

Abstract: Readily assembled and disassembled furniture supported by propping against a wall or other vertical environmental surface. The furniture has vertical legs located on its front side. Shelves or other horizontal members span the legs, and interfit with the legs at grooved joints. The grooves are horizontal, and the shelves slide into engagement with the legs from the rear. The shelves are notched to cooperate with the legs such that the front and side surfaces of a joined leg and shelf are flush. Knobs projecting downwardly from the shelves occupy dedicated grooves formed in the legs. The knobs prevent lateral horizontal displacement of the shelves, while eliminating the need for precision at the notched joints. Assembly is most readily performed with the legs lying on the floor, face down. After the shelves are slid into place, the assembled furniture is tilted into an upright orientation, and propped against the wall. The legs support the shelves vertically.

Abstract: A digital radio system is described in which data symbols are transmitted over a radio channel using multi-level modulation. A receiver receives the multi-level modulation signal and a first symbol estimator gives a first estimate of a symbol represented by the received multi-level modulation signal and a second estimator gives a second estimate of a symbol represented by said signal; the output of the first estimator is provided when the first and second outputs are the same or have a predetermined relationship and an output based on the output of the second estimator is provided otherwise.