GB452051A - Improvements in microphones - Google Patents

Abstract

452,051. Microphones. MIDGLEY, A. H., 9, Priory Hill Avenue, Wembley, Middlesex. Feb. 20, 1935, Nos. 5478, 7834, and 20354. [Class 40 (iv)] A microphone comprises one or more units, each of shallow box-like form constituting an air-tight compartment and arranged so that the incident sound-waves impinge directly on the end surfaces of small area of the unit while the compression and rarefaction phases, of the waves act upon the relative ly much larger areas lying in planes substantially parallel to the direction of travel of the waves. The condenser microphone unit, Figs. 1, 5, comprises metal plates a, b secured on opposite sides of a rectangular spacer member c to form a shallow air-tight box - member, provided with holes by which the unit is threaded on to supporting members e carried on an insulating base g. The units are spaced by members f and each unit is mounted so that the incident sound waves impinge on the edges of the box-like members, the sides of the box being subjected to the consequent waves of compression and rarefaction. In a modified form, Figs. 6, 9, 11, the unit comprises a metal plate i formed with apertures i<1>, a diaphragm k of thin aluminium, an insulation frame with apertures corresponding to the apertures i<1>, an insulation cover and a central electrode member o, mounted in superposed relation. The electrode member is formed by a sheet of a phenolic condensation product in which is moulded an electrode having plates n which register with the openings in the plate i. In a modified form, Figs. 15, 16, the electrode member t has metallic plates s joined by narrow neck portions s<1> and an annular opening t<1> which communicates through holes r<1> in the insulation cover r with the space beneath the diaphragm. The shallow box-like member may be filled with carbon granules, and in the form shown in Figs. 6 to 11 the insulating cover is omitted.