Active noise reduction headphone
An active noise reduction earphone includes a speaker, a plurality of microphones and a feedback system. Each microphone is displaced from the speaker and the other microphones, and each microphone generates a microphone signal responsive to received acoustic noise. The feedback system receives a combination of the microphone signals and generates an inverse noise signal that is applied to the speaker. The speaker generates an inverse acoustic noise signal that substantially cancels the acoustic noise signal at a predetermined location relative to the speaker and the microphones. The feedback system can include a microphone signal combiner in communication with the microphones. The microphone signal combiner generates a signal that may be a sum or weighted sum of the microphone signals and can be used to generate the inverse noise signal. The earphone has an increased noise reduction bandwidth and improved cancellation capability relative to conventional earphones.
1. An active noise reduction earphone, comprising:
a speaker configured to generate an acoustic signal in response to a speaker input signal;
a plurality of feedback microphones each fixed in location relative to the speaker and to each of the other feedback microphones, each of the feedback microphones configured to generate a microphone signal in response to an acoustic noise signal received at the feedback microphone; and
a feedback system in communication with the speaker and the plurality of feedback microphones, the feedback system combining the microphone signals generated by the plurality of feedback microphones into a single feedback error signal and generating the speaker input signal in response to the single feedback error signal, wherein the speaker input signal comprises an inverse noise signal to generate an inverse acoustic noise signal at the speaker that reduces the acoustic noise signal at a predetermined location relative to the speaker and the feedback microphones.
2. The active noise reduction earphone of claim 1 wherein one of the feedback microphones is disposed at a location proximate to the speaker and another one of the feedback microphones is disposed at a location remote to the speaker.
3. The active noise reduction earphone of claim 1 wherein the speaker input signal comprises an audio signal and the inverse noise signal.
4. The active noise reduction earphone of claim 1 further comprising an earphone body.
5. The active noise reduction earphone of claim 4 wherein the earphone body comprises one of a circumaural earphone body, a supra-aural earphone body and an intra-aural earphone body.
6. The active noise reduction earphone of claim 1 wherein one of the feedback microphones is disposed at a location where an acoustic pressure caused by the inverse acoustic noise signal at the location is substantially equal to an acoustic pressure caused by the inverse acoustic noise signal inside the ear canal.
7. The active noise reduction earphone of claim 1 wherein the feedback system comprises a microphone signal combiner in communication with the plurality of feedback microphones.
8. The active noise reduction earphone of claim 7 wherein the microphone signal combiner generates a signal that is a sum of the microphone signals generated by the plurality of feedback microphones.
9. The active noise reduction earphone of claim 8 wherein the microphone signal combiner applies a weight to at least one of the microphone signals and wherein the sum of the microphone signals is a weighted sum.
10. The active noise reduction earphone of claim 8 wherein the microphone signals are electrical current signals provided at an output of each of the feedback microphones and wherein the microphone signal combiner comprises a resistance load that is common to the outputs of the feedback microphones.
11. The active noise reduction earphone of claim 8 wherein the microphone signals are voltage signals and wherein the microphone signal combiner comprises a serial configuration of resistive loads, the voltage signal from each of the feedback microphones being provided across a respective one of the resistive loads.
12. The active noise reduction earphone of claim 8 wherein the microphone signal combiner comprises a microprocessor configured to perform digital addition.