Electrodynamic transducer usable as loudspeaker or microphone - has coil formed as printed circuit group of spirals on both faces of membrane above alternating concentric magnetic poles

摘要

The device may be used as a microphone or speaker and comprises a cup-shaped base closed by a cover with a circular flexible plastics membrane secured between the two. The base contains a circular soft iron or steel magnetic shunt which supports a number of annular permanent magnets concentric with a central magnet and separated and secured by a plastics filling. The magnets present alternate poles several centimetres below the membrane. The membrane has a number of series connected concentric spiral conductor groups formed on one or both surfaces by printed circuit techniques, each group on a surface being 'wound' in the opposite direction to each adjacent group with the outermost group connecting with a terminal. The groups are positioned 'between' the magnet poles with the centre group on each surface being interconnected through a metallised hole. Multiple insulated layers of groups may be provided.