Abstract: A hearing aid is described which comprises an outer front opening and an outer rear opening which are connectable to the respective sides of a membrane in a microphone within the housing of the hearing aid for directional use, and mechanical means for closing the outer rear opening for omnidirectional use, in which said closing means is formed and arranged so as in the closing position thereof to establish a narrow acoustically dimensioned sound passageway from the outer opening not closed to the side of the membrane corresponding to the closed outer opening. According to one embodiment, the mechanical closing means is a slide displaceable along the housing wall in which the opening to be closed is formed, and in which the narrow acoustically dimensioned passageway is an elongated recess in the displaceable slide.

Abstract: A hearing aid for individuals with a loss of sensitivity to the higher frequencies acoustically attenuates the lower frequencies by providing a sound reproducer coupled to a sound delivering conduit provided with an aperture of prescribed size coupled to a cavity which surrounds the sound reproducer.