Abstract: In a moving coil loudspeaker of the type including a pair of co-axial speech coils, one driving a cone and the other a high-frequency diaphragm at the rear of the loudspeaker, the speech coils operating in respective annular air gaps in series with one another and formed in a magnetic assembly comprising an outer ring magnet, a pair of annular magnetic plates fitted at the ends of the ring magnet and a central magnetic pole piece formed with an axial passage defining a horn for the acoustic output of the diaphragm and extending into the openings in the annular plates to define the two air gaps, the central pole piece is formed with an encircling flange forward of its rear end which is secured to the rear annular plate by way of a non-magnetic member to constitute the sole fixing for the pole piece.

Abstract: A moving coil loudspeaker of the type including a pair of co-axial speech coils, one for driving a high frequency diaphragm at the rear of the loudspeaker to provide an output along a horn and the other for driving a cone forming a continuation of the horn and reproducing the lower frequencies has an acoustic lens fitted in the region where the horn contour is taken over by the cone, the lens being shaped over its external surface so as to conform snugly with the contour of the cone and being effective to increase the divergence of the beam of acoustic radiation from the horn in the operative plane of the lens. The acoustic lens is preferably so designed that the divergence of the acoustic beam from the horn matches that from the cone and may be of the slant-type, being held by a cruciform mounting extending across the mouth of the horn proper.

Abstract: An electro-acoustic transducer having a sound-generating diaphragm and means for driving the diaphragm in which the diaphragm is provided with perforations filled with damping material to oppose the formation of standing waves in the diaphragm. The perforations are arranged in between three and eight generally radially extending curved bands, each band being formed of a plurality of parallel rows of perforations extending along the length of the band.