DIRECTIONAL MICROPHONE FOR HEARING AID

• US 3,662,124 A
• Filed: 09/25/1970
• Issued: 05/09/1972
• Est. Priority Date: 06/05/1967
• Status: Expired due to Term

• Current Assignee: Johannes Wittkowski, Otto Hassler
• Original Assignee: Johannes Wittkowski, Otto Hassler
• Inventors: Hassler, Otto, Wittkowski, Johannes
• Primary Examiner(s): Claffy, Kathleen H.
• Assistant Examiner(s): Kundert, Thomas L.
• Application Number:
  US05/075,548
• Time in Patent Office: 592 Days
• Field of Search: 179/179,180,1DM,121D,107,121R 181/31R
• US Class Current: 381/357
• CPC Class Codes: H04R 1/38 in which sound waves act upon both sides of a diaphragm and incorporating acoustic phase-shifting means, e.g. pressure-gradient microphone

Abstract

The disclosure is directed to an improvement in a microphone used primarily in head-worn hearing aids in which the microphone achieves a directional characteristic. The chamber and aperture in front of the diaphragm or other speech-responsive member is constructed in the normal manner while the chamber to the rear of the diaphragm or other speech-responsive member has a plurality of hollow elongated members secured within the walls of the microphone housing. The elongated members may be formed from sintered porous material such as metal, glass, or plastic, and may be arranged side-by-side or in a honeycomb arrangement. The elongated members attenuate the propagation of the sound waves, the attenuation being approximately 20 decibels lower than that reaching the other side of the diaphragm or other speechresponsive member without materially changing the inherent response characteristic of the microphone.

Claims

1. An improved miniature microphone constructed and arranged to be used in a hearing aid housing to be worn on the head of the wearer wherein the improvement comprises:

a miniature elongated microphone housing having a substantially enclosed end and an open end, said enclosed end having a sound admitting aperture formed therein which is considerably smaller than said open end, a sound pressure-responsive member secured to said housing and disposed between said ends to define first and second chambers therebetween, said pressure-responsive member adapted to be coupled to a transducer for movement by sound waves;

a transducer for producing electrical signals representative of sound waves operably connected to said sound pressureresponsive member and secured within said second chamber in said housing; and

a propagation-retarding acoustic resistance mechanism disposed within and obstructing said open end of the housing, said mechanism forming a plurality of narrow elongated passages, each having substantially the same length to admit the sound waves to said sound pressure-responsive member, said mechanism containing a plurality of elongated elements in juxtaposition arrangement forming said plurality of narrow elongated passages and extending between the open end of said housing and said transducer in said second chamber, said transducer producing electrical signals from sound waves received through said acoustic resistance mechanism which has a frequency response having a profile substantially the same as that produced by said transducer from sound waves received from said aperture.

2. The invention set forth in claim 1 wherein said open end of the housing having said propagation-retarding acoustic resistance mechanism disposed therein has a cross-sectional area substantially equal to the effective area of said sound pressure-responsive member.

3. The invention set forth in claim 1 wherein said propagation-retarding acoustic resistance mechanism produces an acoustic attenuation having a means value of substantially 20 decibels higher than that for sound waves entering the aperture of the substantially enclosed end of the housing.

4. A microphone for a hearing aid to be worn on a person'"'"''"'"'s head for detecting A sound and discriminating the direction of the source of the sound, comprising a sound pressure-responsive diaphragm having opposite sides, an electric signal-generating transducer connected to the diaphragm and producing such signals in response to diaphragm movement, a housing confining and mounting the diaphragm and defining open and substantially enclosed chambers respectively disposed at the opposite sides of the diaphragm, the housing having a sound admitting aperture communicating with the substantially enclosed chamber, the open chamber being disposed to the rear of the diaphragm and having an open end to face away from the source of sound, the housing defining unobstructed space adjacent the transducer to freely transmit sound past the transducer and to the diaphragm, and a sound wave propagation-retarding acoustic resistance mechanism obstructing the open rear end of the open chamber, said mechanism including a plurality of elongate and substantially parallel capillaries, the individual capillaries having a size of opening of the order of the size of passages existing between confined camel hairs, and said capillaries being assembled into a block and confined in the elongate open chamber of the housing the open ends of the capillaries confronting the open end of the open chamber to face the direction opposite the source of sound, the sound waves creating minimum and maximum pressures impinging the diaphragm and producing movement thereof, the sound wave propagation being retarded by the resistance mechanism to the extend that at the time the sound waves impinge the front side of the diaphragm with a maximum pressure, the sound waves impinge the back side of the diaphragm with less than maximum pressure, whereby to achieve directional effect with the microphone.

5. The invention according to claim 4 and the overall open cross section of the capillaries corresponding approximately to the effective area of the diaphragm.

6. The invention according to claim 4 and the overall open cross section of the capillaries being approximately the same as the effective area of the open end of the open chamber.

7. The invention according to claim 4 and the dimensions of the propagation wave-retarding resistance mechanism including the capillaries being dimensioned to maximize the ration of the sound wave pressures applied against the front of the diaphragm in relation to such pressures applied to the back of the diaphragm.

8. A microphone for a hearing aid to be worn on a person'"'"''"'"'s head for detecting a sound and discriminating the direction of the sound, comprising, a sound pressure-responsive diaphragm having front and back sides, an electric signal-generating transducer connected to the diaphragm and producing such signals in response to diaphragm movement, a housing confining and mounting the diaphragm and defining open and substantially enclosed chambers respectively disposed at the back and front sides of the diaphragm, the housing having a sound-admitting aperture communicating with the substantially enclosed chamber, the open chamber being elongate and disposed at the rear of the housing and having an open rear end to face away from the source of the sound and for admitting sound for propagation to the back side of the diaphragm, a sound wave propagation-retarding acoustic resistance mechanism obstructing the open rear end of the open chamber, said mechanism including a plurality of elongate and substantially parallel capillaries, the individual capillaries having a size of opening of the order of the size of the discrete passages existing between confined camel hairs, said capillaries being assembled into a block and confined in the elongate open chamber of the housing, the capillaries in the block extending generally longitudinally of the chamber and toward the open end thereof, the open ends of the capillaries confronting the open end of the chamber to face the direction opposite the source of sound, the sound waves cReating maximum and minimum pressures impinging the diaphragm and producing movement thereof, the sound wave propagation being retarded by the resistance mechanism to the extent that at the time the sound waves impinge the front side of the diaphragm with a maximum pressure, the sound waves impinge the back side of the diaphragm with substantially minimum pressure, to thereby substantially maximize the ratio of sound wave pressure applied against the front and back sides of the diaphragm, whereby to achieve a significant directional effect with the microphone.

9. A directional microphone for use in a hearing aid to be worn on a person'"'"''"'"'s head, comprising:

a diaphragm sensitive to sound pressure;

a diaphragm-operated transducer generating electric signals related to the sound pressures sensed by the diaphragm;

a microphone housing enclosing the diaphragm and defining front and rear chambers at opposite sides of the diaphragm, the housing having a sound opening communicating with the front chamber and freely admitting sound pressures to impinge upon the diaphragm; and

means defining clear passages into the rear chamber of the housing at a location remote from the sound opening said passages having a size admissive to sound pressures and also resistive to transmission of such sound pressures to retard impingement of the sound pressures against the diaphragm, the retardation effected by the clear passages causing sound pressure from the preferred direction acting upon the rear of the diaphragm being at a minimum level while sound pressure admitted through the sound opening at the rear of the diaphragm reaches a maximum level.