Directional microphone for head mounted midget hearing aids

Claim 1

A directional microphone for head-mounted eyeglass and behind-the-ear hearing aids, comprising: a rigid metal casing of box-like configuration, the casing having front and rear portions including rigid walls with exterior and interior surfaces and the walls defining front and rear access openings into the casing, the front access opening in the wall of the front portion providing substantially unrestricted sound access into the casing, the rear access opening in the wall of the rear portion being many times larger than required to provide sound access into the casing, a vibratable diaphragm in the casing and dividing the interior of the casing into two chambers, said diaphragm being disposed between said access openings and restricting air communication across the interior of the casing and between said two chambers, the diaphragm being coupled to transducer means in one of the chambers to produce electric signals in response to vibration of the diaphragm, and a discrete plate larger than said rear access opening and constructed of thin foil-like metal in contrast to the rigid metal walls of the casing, said discrete plate overlying and obstructing the entire rear access opening in the wall of the rear portion of the casing and continuously secured around the entire periphery of the plate to the exterior surface of the casing, said discrete plate having a multiplicity of minute apertures therethrough, each of said apertures having substantially the same size as adjacent apertures and each of said apertures providing open communication from the exterior of the casing and directly and linearly through the rear access opening and into the adjoining chamber within the casing, and said multiplicity of minute apertures cumulatively defining the sole acoustic resistance coordinated with the volume of the chamber between the discrete foil plate and the diaphragm to cooperatively produce a time delay for sounds entering the minute apertures to the time at which the sounds are effective for moving the diaphragm, and the peripheries of the minute apertures in the discrete foil plate being tapered in a direction through the thickness of the foil plate to minimize the effect of the thickness of the foil plate upon the resistance offered to passage of sound.