Planar diaphragm loudspeakers have been in use for over twenty years but have never achieved the same popularity as cone-type speakers, due primarily to their cost and to their size and different performance characteristics.
Numerous examples of such speakers may be found in the patent literature, for example, U.S. Pat. No. 3,674,946 Winey, U.S. Pat. No. 3,919,499 Winey, U.S. Pat. No. 3,829,623 Willis et al, U.S. Pat. No. 4,468,530 Torgeson and U.S. Pat. No. 4,471,172 Winey. The last mentioned patent illustrates the structure of a typical planar diaphragm speaker, which comprises a polyester film diaphragm, a current carrying conductor adhered to the diaphragm, spaced bar magnets for generating a magnetic field which intersects the conductor, with the conductor typically being positioned in alignment with the gaps between the bar magnets. When an exciting current passes through the conductor, the diaphragm will be vibrated by the reactive forces generated by the interfering magnetic fields surrounding the conductor and between the adjacent bar magnets.
Most existing planar diaphragm speakers in commercial production utilize polyester film, such as Mylar (registered trade mark) having a thickness of the order of 0.01 mm to 0.1 mm. The present applicant believes that the quality of sound produced by speakers constructed in this way is to a certain extent colored by the use of polyester film or similar materials. Furthermore, the use of such materials results in manufacturing difficulties, such as the ease with which the film may be properly tensioned and the care with which the film must be handled during manufacture.