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Directional microphone assembly
| Details |
Inventors: Killion, Mead C.; Stewart, Jonathan; Wilson, Don; Roberts, Matthew J.; Iseberg, Steve; Monroe, Timothy S.;
Assignee: Etymotic Research, Inc. (Elk Grove Village, IL)
Primary Examiner: Tran; Sinh
Assistant Examiner:
Attorney, Agent or Firm: McAndrews, Held & Malloy, Ltd.
A microphone capsule for an in-the-ear hearing aid is disclosed. The capsule can include a top plate having first and second spaced openings defining front and rear sound inlets, and a directional microphone cartridge enclosing a diaphragm. The diaphragm is oriented generally perpendicular to the top plate and divides the directional microphone cartridge housing into a front chamber and a rear chamber. A front sound passage communicates between the front sound inlet and the front chamber, and a rear sound passage communicates between the rear sound inlet and the rear chamber. Front and rear acoustic damping resistors having different resistance values are associated with the front and rear sound passages. The acoustic resistor pair provides a selected time delay, such as about 4 microseconds, between the front and rear sound passages. The use of two acoustic resistors instead of one levels the frequency response, compared to the frequency response provided by a rear acoustic damping resistor alone. |
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DETAILED DESCRIPTION OF THE INVENTION DESCRIPTION OF THE PREFERRED EMBODIMENTS Certain elements of the functions of the present invention, in particular the use of a switch to choose directional or omnidirectional operation with the same frequency response, were described in Applicant's U.
S.
Pat.
No.
3,835,263, dated 1974.
The combination of directional and omnidirectional microphones in a hearing aid with an equalization circuit and a switch to provide switching between omnidirectional and directional responses with the same frequency response was described in Applicant's U.
S.
Pat.
No.
5,524,056, 1996.
The disclosures of these two patents are incorporated herein by reference.
A hearing aid apparatus 100 constructed in accordance with one embodiment of the invention is shown generally at 10 of FIG.
1.
As illustrated, the hearing aid apparatus 10 utilizes a microphone capsule 40, a switch 55 to select the directional-microphone or omni-directional microphone outputs of capsule 40, and a windscreen 90 to reduce the troublesome effects of wind noise.
FIG.
2 shows more of the construction of capsule 40, consisting of a top plate 80 (defining an exterior portion of said capsule as worn), a cylinder or housing 50 and an equalization circuit 60.
FIG.
3 shows a subassembly 45 of one embodiment of the capsule 40 of the present invention, showing a top plate 80 with sound tubes 85 and 86 coupling sound inlets 83, 84, to the front chamber 22 and the rear chamber 24 of microphone cartridge 20.
Adhesive 27 seals tubes 85 and 86 to microphone cartridge 20.
Microphone cartridge 20 is mounted with the plane of the diaphragm 21 generally normal to the top plate 80.
This configuration eliminates the need for the prior art metal inlet tube or tubes of the microphone and provides a smaller distance D (measured as shown in FIG.
17 of the '056 patent) than would be possible using prior art constructions.
As a result, the diameter of capsule 40 may be maintained a 0.
25 inches or less.
Also shown is sound inlet 88, to which omnidirectional microphone cartridge 30 (not shown) is to be connected
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