Apparatus and method for matching the response of microphones in magnitude and phase

• US 20030198356A1
• Filed: 04/29/2003
• Published: 10/23/2003
• Est. Priority Date: 08/25/1998
• Status: Active Grant

• Current Assignee: Knowles Electronics Llc (Knowles Corporation)
• Original Assignee: Knowles Electronics Llc (Knowles Corporation)
• Inventors: Thompson, Stephen C.
• Granted Patent: US 7,113,604 B2
• Time in Patent Office: Days
• US Class Current: 381/92
• CPC Class Codes: H04R 25/407 Circuits for combining signals of a plurality of transducers
• CPC Class Codes: H04R 29/006 Microphone matching
• CPC Class Codes: H04R 3/005 for combining the signals of two or more microphones specially adapted for hearing aids H04R25/407
• CPC Class Codes: H04R 3/04 for correcting frequency response

Abstract

An apparatus is provided for matching the response of a pair of microphones. The two microphones provide a first and second output, respectively, in response to an audible input. The microphone outputs are subtract from each other to produce a gain control output for operably controlling the gain of the first microphone output, resulting in a gain compensated microphone output. A phase adjustment circuit also is provided responsive to the gain compensated microphone output and a rolloff control output for producing a matching output. The rolloff control output is generated by a phase difference subtractor circuit responsive to both the matching output and the second microphone output. Moreover, the output of at least one of the microphones has a resonance frequency that is shifted to a desired preselected frequency.

Claims

1. A device for receiving an audible input comprising:

a hearing aid housing;

a first microphone operably attached to the hearing aid housing and having an output responsive to the audible input;

a second microphone operably attached to the hearing aid housing and having an output responsive to the audible input;

a phase adjustment circuit responsive to the first microphone output and a rolloff control output for producing a compensated microphone output; and

a subtractor circuit responsive to the compensated microphone output and the second microphone output for generating the rolloff control output.

2. The device of claim 1, further comprising a bandpass filter operably connected between the subtractor circuit and the compensated microphone output.

3. The device of claim 2, further comprising a bandpass filter operably connected between the subtractor circuit and the second microphone output.

4. The device of claim 3, further comprising a buffer operably connected to the compensated microphone output.

5. The device of claim 4, further comprising a buffer operably connected to the second microphone output.

6. The device of claim 1, further comprising a feedback circuit operably connected to the compensated microphone output and the phase adjustment circuit.

7. The device of claim 6, wherein the said feedback circuit includes a capacitor.

8. The device of claim 1, wherein the outputs of the microphones have a resonance frequency and a circuit is operably connected to at least one of the microphones for shifting the resonance frequency within the output of the microphone.

9. A circuit for shifting the rolloff of a microphone comprising:

an input terminal for receiving an output from the microphone;

an amplifier having an inverting input and an output;

a gain control circuit operably connected between the input terminal and the inverting input of the amplifier for adjusting the gain of the microphone output; and

a feedback circuit operably connected to the output of the amplifier and the inverting input, the feedback circuit including a feedback adjustment circuit responsive to a rolloff control output.

10. The device of claim 9, wherein said feedback circuit includes a capacitor.