MICROPHONE ASSEMBLY OPERABLE IN DIRECTIONAL AND NON-DIRECTIONAL MODES

• US 3,835,263 A
• Filed: 02/05/1973
• Issued: 09/10/1974
• Est. Priority Date: 02/05/1973
• Status: Expired due to Term

• Current Assignee: Knowles Electronics Incorporated 1151 Maplewood Dr Itasca IL
• Original Assignee: Mead Clifford Killion
• Inventors: Killion, Mead Clifford
• Primary Examiner(s): Blakeslee, Ralph D.
• Application Number:
  US05/329,673
• Time in Patent Office: 582 Days
• Field of Search: 181/23 179/17FD,17S,17E,17H
• US Class Current: 381/313
• 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
• CPC Class Codes: H04R 25/402 using contructional means

Abstract

A microphone assembly being selectively operable in directional and non-directional modes; and, having similar response characteristics relative to frequency whether operating in one or the other mode.

Claims

1. A microphone assembly selectively operable in directional and non-directional modes, comprising, in combination, diaphragm means positioned to have its front and back sides responsive to sound coupled thereto, at least two spaced sound inlets and at least two sound ports, means providing acoustical communication between said sound inlets and said sound ports, sound entering a first sound port being effective on the front side of said diaphragm, and sound entering a second sound port being effective on the back side of the diaphragm whereby said microphone assembly functions in a directional mode, means for selectively interrupting acoustical communication between the second sound inlet and the second sound port whereby said microphone assembly functions in a non-directional mode when communication between the second sound inlet and the second sound port is interrupted, and an acoustical communication path including an impedance means therein for controllably conveying sound from said first sound inlet to the second sound port to thereby obtain substantially the same response characteristics relative to frequency when the microphone assembly is operated in a directional as when it is operated in a non-directional mode.

2. A microphone assembly as in claim 1 further including an acoustical impedance positioned in said second sound port to provide an acoustical phase shift.

3. A microphone assembly as in claim 1 wherein the sound conveyed by said acoustical communication path to said second port and the other side of the diaphragm has minimal effect when said second sound inlet is open.

4. A microphone assembly as in claim 1 wherein adjustable vane means are provided for interrupting said acoustical communication.

5. A hearing aid microphone assembly selectively operable as a directional device and as a non-directional device comprising at least a pair of spaced sound inlets, a microphone having a diaphragm and at least two sound ports communicating to respectively opposite sides of a diaphragm, means for coupling sound from the first sound inlet to the first sound port, an acoustical communication path including an acoustical impedance means therein for controllably coupling sound from the first inlet to the second sound port, means coupling sound from the second sound inlet to the second sound port, and means for selectively closing and opening said second inlet to cause said hearing aid microphone assembly to function as a non-directional and a directional mode respectively, and the acoustical impedance of said acoustical communications path providing an acoustical match whereby said hearing aid microphone assembly develops substantially the same response characteristics relative to frequency when it is functioning in a directional mode as when it is functioning in a non-directional mode.

6. A hearing aid as in claim 5 wherein said acoustical passage comprises an elongated tube having one end connected to a sound inlet of the housing and the other end connected to a first port of the microphone.

7. A microphone assembly comprising diaphragm means, first and second sound ports acoustically communicating with opposite sides of the diaphragm means, first and second sound inlets respectively communicating with the first and second ports, one of said sound inlets being selectively openable and closeable to cause said microphone assembly to function as a directional and non-directional device respectively, and auxiliary acoustical communication path means including impedance means for enabling said microphone assembly to have substantially the same characteristic response relative to frequency whether it is functioning as a directional or non-directional device.

8. A microphone assembly as in claim 1 wherein said microphone assembly is mountable on a heAd worn hearing aid and said openings are in a fore and aft relatively spaced relation, whereby by the maximum response sensitivity is in a direction toward the front of the wearer.

9. A microphone assembly as in claim 1 wherein the sound pressure level effective on the back side of the diaphragm from sound entering through one sound inlet is less than the pressure level effective on the back side of the diaphragm from sound entering through the other sound inlet.

10. A microphone assembly as in claim 1 wherein the sound pressure level input from the second sound inlet to the second sound port is sufficiently high such that when there is acoustical communication therebetween, sound coupled from the first sound inlet to the second sound port has minimal effect.

11. A microphone assembly as in claim 1 comprising a housing, the diaphragm mounted in said housing to provide a front and back cavity, a bulkhead mounted in the housing to provide a distinct and separable sound communication paths between said sound inlets and said sound ports, an acoustical impedance in one of said paths and means including said bulkhead forming a chamber in said communication path and cooperating with said back cavity to effect the characteristic response of said assembly.

12. A microphone assembly as in claim 7 further including a chamber formed between said second sound opening and said second sound port, a cavity formed between said second sound port and said diaphragm means, said chamber being relatively small as compared to said cavity whereby the transistion from one mode to the other mode will have the effect of shifting the response characteristic at the upper end of the frequency range.

13. A microphone assembly as in claim 12 wherein the chamber is relatively large as compared to said cavity thereby providing a minimal difference in the operating characteristics whether the microphone is operating in the directional mode or in the non-directional mode.

14. A microphone assembly as in claim 7 including a first chamber between the front sound opening and the second sound port, vane means in said first chamber and operable to a first position for closing the rear sound opening to cause the microphone to operate in a non-directional mode, the vane means operable to a second position for closing the acoustical communication between the front sound opening and the rear sound port to cause the microphone to operate in a directional mode, a second chamber formed between the rear sound opening and the rear sound port when said vane means is in the second position whereby some loss in frontal sensitivity is realized when operating in a non-directional mode while the frequency response characteristic curves of the assembly for either mode remain substantially the same.

15. A hearing aid as in claim 5 wherein a first acoustical cavity is formed between said first sound opening and said first sound port, a second cavity is formed between said second sound opening and said second sound port, acoustical impedance means mounted between said sound cavities, and said microphone having an internal cavity formed behind the acoustical element of said sound port and assuring that the second cavity is substantially larger than the internal cavity thereby to assure that there is minimal difference in the sensitivity and frequency characteristics irrespective of the operating mode of the hearing aid.