The kone loud speaker

The stalloy pole pieces used in this instrument are polarised by a large permanent magnet, an armature being suspended centrally in the air gap, so that it is only subjected to a magnetic pull when a current flows through the coils; the vibration of the armature is communicated to the diaphragm by push rods and levers. There is no horn, but a large diaphragm consisting of paper cones cemented around the bases which are approximately 18 in. in diameter. The apex of the cone is made to hold a push rod of the magnet system. The modes of vibration of the diaphragm are discussed. Best results are obtained from an amplifier having an impedance of about 2000 ohms, which gives impedance matching at about 300 cycles per second; where it is used with valves of low-power handling capacity, a suitable transformer should be used to reduce the output impedance of the amplifier to 2000 ohms.