Hearing aid with directional microphone system

Claim 2

In a hearing aid, a highly directional microphone system comprising: acoustic conduit means defining a front-to-back sound conduit through the hearing aid; a microphone assembly including a housing and diaphragm means coupled to transducer means for translating mechanical vibrations acoustically induced in said diaphragm means into corresponding electrical signals; and support means for supporting said microphone assembly in said conduit such that said assembly is substantially isolated from stray mechanical energy in the hearing aid, but such as to define a passageway for the conduction of sound waves of audible frequencies around said microphone assembly without substantial impedance thereof, said housing for said microphone assembly having a front orifice which communicates exclusively with one side of said diaphragm means and which presents a predetermined acoustic impedance to sound waves, at least those in low and middle ranges of audible frequencies, propagating in said passageway, said housing for said microphone assembly also having a rear orifice which communicates exclusively with the opposite side of said diaphragm means, which is effectively spaced from said front orifice by a predetermined acoustic path length which is such that sound waves, at least those in said low and middle ranges of audible frequencies reaching opposite sides of said diaphragm means through said front and rear orifices establish a pressure gradient across said diaphragm means, and which has a predetermined acoustic impedance greater than said acoustic impedance of said front orifice and of such magnitude as to produce a highly directional characteristic for the hearing aid.

Claim 3

The apparatus defined by claim 1 wherein said rear orifice is a slit.

Claim 4

In a behind-the-ear hearing aid having an electroacoustic transducer, a highly directional microphone system comprising: a microphone assembly having a box-like housing with front and rear wall panels, said assembly also including diaphragm means coupled to transducer means for translating mechanical vibrations acoustically induced in said diaphragm means into corresponding electrical signals; microphone casing means substantially surrounding said microphone assembly except for front and rear openings disposed to admit sound waves to said microphone assembly; and visco-elastic cushioning means positioned between said housing and said casing means for isolating said microphone assembly from stray mechanical energy in said casing means and for spacing said microphone assembly from said casing means, to define an interstitial sound-transmissive passageway around said microphone assembly, said front panel of said housing for said microphone assembly having a relatively large front orifice which communicates exclusively with one side of said diaphragm means and which presents a predetermined first acoustic impedance to sound waves, at least those in low and middle ranges of audible frequencies propagating in said passageway, said rear panel of said housing for said microphone assembly having a slit-like rear orifice which communicates exclusively with the opposite side of said diaphragm means, which is effectively spaced from said front orifice by a predetermined acoustic path length which is such that sound waves, at least those in said frequency ranges, reaching opposite sides of said diaphragm means, through said front and rear orifices establish a pressure gradient across said diaphragm means, and which rear orifice has a predetermined acoustic impedance greater than said acoustic impedance of said front orifice and of such magnitude as to produce a highly directional characteristic for the hearing aid.

Claim 5

In a behind-the-ear hearing aid having an electroacoustic transducer, a highly directional microphone system comprising: a microphone assembly having a box-like housing with front and rear wall panels, said assembly also including diaphragm means coupled to transducer means for translating mechanical vibrations acoustically induced in said diaphragm means into corresponding electrical signals; microphone casing means substantially surrounding said microphone assembly except for front and rear openings disposed to admit sound waves to said microphone assembly; and visco-elastic cushioning means positioned between said housing and said casing means for isolating said microphone assembly from stray mechanical energy in said casing means and for spacing said microphone assembly from said casing means, to define an interstitial sound-transmissive passageway around said microphone assembly, said front panel of said housing for said microphone assembly having a relatively large front orifice which communicates exclusively with one side of said diaphragm means and which presents a predetermined first acoustic impedance to sound waves, at least those in low and middle ranges of audible frequencies propagating in said passageway, said rear panel of said housing for said microphone assembly having a slit-like rear orifice which communicates exclusively with the opposite side of said diaphragm means, which is effectively spaced from said front orifice by a predetermined acoustic path length which is such that sound waves, at least those in said frequency ranges, reaching opposite sides of said diaphragm means, through said front and rear orifices establish a pressure gradient across said diaphragm means, and which rear orifice has a predetermined acoustic impedance greater than said acoustic impedance of said front orifice and of such magnitude as to produce a highly directional characteristic for the hearing aid.

Claim 6

The apparatus defined by claim 3 wherein said rear orifice is a slit having a smaller dimension of approximately 0.0015 inch.

Claim 7

The apparatus defined by claim 3 wherein said rear orifice has length and width dimensions of approximately 0.050 and 0.0015 inch, respectively.

Claim 8

The system defined by claim 5 wherein said casing means is a thin metal can.

Claim 9

In a hearing aid having a protective shell, the system defined by claim 5 wherein said casing is plastic and is integral with said shell.