GB1412597A - Microphone damping - Google Patents

Abstract

1412597 Microphones; acoustic impedance elements PLESSEY DUCON PTY Ltd 22 Nov 1972 [23 Nov 1971] 53914/72 Headings H4J and H3U An acoustic impedance element comprises a mesh having apertures of substantially uniform dimensions, the aperturesbeing closed over one or more selected areas of the mesh by means of a coating on the selected area or areas of the mesh. Preferably photo-sensitive material is applied to the whole of a metal mesh to block all the apertures. Using a mask, one or more suitable areas of the mesh are exposed to light. The photo-sensitive material is subsequently removed from the exposed area or areas. A microphone comprises a metal case 10, a perforated cover 12 and connecting pins 13. An encapsulated integrated circuit amplifier 15 is connected by leads 14 to a diaphragm 17 comprising a thin piezoelectric disc bonded to a metal disc. A disc 20, to which is adhered a partly closed metal mesh 21, is spaced from the diaphragm 17 by a spacing ring 16a. A further annular spacer 22 spaces disc 20 from a disc 23 to which is adhered a partly closed metal mesh 24. A plastics membrane 26 protects the microphone from saliva or humidity. An inner cavity bounded by spacing rings 16a damps a natural resonance in the region 3 to 4 kHz. The cavity bounded by spacer 22 controls resonance in the region of 12 kHz.