GB1057853A - Improvements in or relating to hearing aids - Google Patents

Abstract

1,057,853. Electro-mechanical, transducers; diaphragms. A. P. BESSON & PARTNER Ltd. Sept. 25, 1963, No. 37762/63. Heading H4J. A microphone comprises a ferromagnetic box-like casing containing a U-shaped armature having parallel arms 8, 9, the arm 9 being adjacent one face of the casing and secured at one end 13 thereof, the intermediate web being supported by the casing through a tab 10. A coil 17 encircles the arm 8. A U-shaped polepiece 14 carrying permanent magnets 15, 16 is affixed to the arm 9 and embraces the arm 8. A silver-plated beryllium copper drive pin 21 connects the arm 8 to a diaphragm 22 extending across the casing. Sound waves enter the casing through an aperture 32. In a similarly constructed earphone the magnets 15, 16 and, if desired, the coil 17, are mounted on the arm 8. Sound waves are conducted through a tube attached to the aperture 32 to a person's ear, or the distribution of masses and stiffnesses may allow energy transfer to the mastoid bone. A tool may be inserted through a window 31 to bend an extension 30 of the armature to adjust the polepiece 14. The thickness of the silver layer on the pin 21, and thus the moving mass, may be adjusted by rolling. The diaphragm 22 comprises a sheet 24 of polyethylene terephthalate secured to the casing and carrying an aluminium sheet 25 with its centre part raised in an oval bead to provide a tubular space connecting a front opening 27 through the sheet 25 and a rear opening 28 of the sheet 24. This tube permits control of the frequency characteristics by varying the positions of openings 27, 28. The microphone and earphones may be used in a spectacle type of hearing aid. Reference has been directed by the Comptroller to Specification 869,234.