Compression drivers

A compression driver for connection to the throat of an acoustic horn, the compression driver comprising a diaphragm having a concave sound-radiating surface, a phase plug having a convex surface shaped complementarily to match the concave surface of the diaphragm, and a magnet, the diaphragm being connected to a voice coil former along a line forming a closed loop and which lies in a plane, the diaphragm and former being adapted to reciprocate along an axis, the diaphragm, phase plug, voice coil former together being configured to form:

• a compression cavity between the concave surface of the diaphragm and the convex surface of the phase plug;
• a surround cavity bounded by an outer surface of the voice coil former, an inner surface of the magnet and an edge side of the diaphragm outside the voice coil former;
• a magnetic gap transverse to the axis between outer and inner parts of the magnet adjacent the diaphragm through which magnetic gap the voice coil former reciprocates, opening into
• a voice coil former cavity which extends along the axis away from the magnetic gap, the voice coil former cavity having an outer part extending between the outside of the voice coil former and the magnet and an inner part extending between the inside of the voice coil former and the phase plug, the voice coil former cavity leading from the magnetic gap to a magnet cavity,
• in which an abstract surface can be generated by rotating about the axis an abstract line extending from the diaphragm on the line of the closed loop to the convex surface of the phase plug perpendicularly thereto, and in which a plurality of holes are formed in the voice coil former around at least a part of its circumference and pass through the voice coil former to connect the compression cavity with the surround cavity, the holes having a total area substantially the same as or greater than the area of the abstract surface.