Abstract: A wax guard for a hearing aid is mushroom-shaped, having a cross passage through its head which intersects an axial passage in its stem. The axial passage contains an acoustic filter terminating the axial passage in its characteristic impedance. The cross passage is semi-circular in section to reduce the projection of the guard into an ear canal and the total area of the two branches of the passage exiting from the axial passage is equal to that of the axial passage. The guard removably snap fits into a metal ring glued into the outlet port of the hearing aid.

Abstract: A connecting cord has a plug at each end. Either such plug may be plugged into the receptacle of a hearing aid and the other plug may be plugged into an external microphone. The contacts of each plug are connected in a different circuit configuration to the conductors of the cord so that when one plug is plugged into the receptacle, the internal hearing aid microphone is shorted out, and when the other plug is plugged into the receptacle, both microphones operate in parallel. The plug contacts are formed of printed circuit board and each plug has a rocker with a hooked top which engages a slot in the receptacle to prevent the inadvertent movement of the plug out of the receptacle. Other plug internal circuit configurations allow connection of other signalling systems to the hearing aid.