GB1276498A - Improvements in and relating to ear defenders - Google Patents

Abstract

1276498 Ear protectors AMPLIVOX Ltd 22 July 1969 [1 Aug 1968 4 June 1969] 36842/68 Heading A5R [Also in Division H4] An ear defender, which attenuates at least higher frequency components of sound (e.g. above 3,000 Hz) passing to the wearer's ear, includes a rigid shell for placing over the wearer's ear, the shell having a passage for sound waves and acoustic impedance between the outside of the shell and the passage. An acoustic valve is operable selectively to open or close the passage. The rigid shell 1, which incorporates a telephone receiver 11, has a seal 2 consisting of a tube filled with liquid or plastics foam. Ports 3 are provided which may be aligned with ports 5 in a rotatable disc 4 covered with a felt or foamed plastics pad 7 constituting an acoustic resistance. A low pass filter is constituted by the acoustic resistance of the pad 7 and the ports 3, 5 and the capacitance of the air chamber. The pad 7 may be protected by a mesh grill 8 or a thin polyethylene disc. If a polyethylene disc is mounted in non-taut manner explosive loud noises make it taut and it acts as a substantial attenuating impedance. An outer housing 9 holds the parts together and provides a grip for rotation of the valve elements. A spring 10 holds disc 4 and shell 1 in intimate contact. Alternatively, an additional air volume 13 (Fig. 5) and a stiff, relatively heavy diaphragm 14 are provided. A handle 15 (or knob) permits rotation of disc 4. Instead of being stiff and relatively heavy, the diaphragm 14 may be of sheet polyethylene mounted in non-taut manner to provide additional attenuation of explosive noises. The ear defender may be supported by a headband or incorporated in a protective helmet.