Apparatus and method for non-occluded active noise shaping
Non-occluding active noise suppression apparatus and methods are disclosed. A housing includes an inlet to admit ambient sound and an outlet to output personal sound to the ear of a user. An acoustic path and an electronic path are provided from the inlet to the outlet within the housing. For a predetermined frequency range, a phase difference between the acoustic path and the electronic path is substantially 180 degrees.
1. A non-occluding active noise suppression apparatus, comprising:
a housing including an inlet to admit ambient sound and an outlet to output personal sound to the ear of a user;
an acoustic path from the inlet to the outlet within the housing; and
an electronic path from the inlet to the outlet within the housing,
wherein, for an operating frequency range, the electronic path is configured to provide a phase difference between the acoustic path and the electronic path of substantially 180 degrees.
2. The apparatus of claim 1 , wherein, for the predetermined frequency range, the phase difference between the acoustic and the electronic path is within 180±10 degrees.
3. The apparatus of claim 1 , wherein, for the predetermined frequency range, the phase difference between the acoustic and the electronic path is within 180±18 degrees.
4. The apparatus of claim 1 , wherein the acoustic path couples ambient air pressure from the inlet to the outlet.
5. The apparatus of claim 1 , wherein the acoustic path comprises an acoustic delay line.
6. The apparatus of claim 5 , wherein the acoustic delay line comprises a serpentine tube.
7. The apparatus of claim 5 , wherein the acoustic delay line comprises a tube filled with a material in which a speed of sound is lower than a speed of sound in air.
8. The apparatus of claim 1 , wherein the acoustic path comprises a passive low-pass filter.
9. The apparatus of claim 8 , where a cutoff frequency of the passive low-pass filter sets an upper limit of the operating frequency range.
10. The apparatus of claim 1 , where the electronic path comprises:
a microphone to convert a portion of the ambient sound to an ambient audio signal;
an audio processor to process the ambient audio signal to provide a processed audio signal; and
a speaker to convert the processed audio signal to processed sound.
11. The apparatus of claim 10 , further comprising a mixing volume proximate the outlet in which the sound from the acoustic path and the processed sound combine.
12. The apparatus of claim 11 , wherein the processed sound includes anti-sound to cancel at least a portion of the sound from the acoustic path over the operating frequency range.
13. The apparatus of claim 10 , wherein
the acoustic path comprises a passive low-pass filter, and
a cutoff frequency of the passive low-pass filter is less than or equal to a resonant frequency of the speaker.
14. The active acoustic filter of claim 1 , wherein:
the housing is an earbud housing configured to fit, at least partially, within and be supported by the ear of the user.
15. A method for suppressing noise, comprising:
providing a housing including an inlet to admit ambient sound and an outlet to output personal sound to the ear of a user;
conveying a portion of the ambient sound along an acoustic path within the housing from the inlet to the outlet; and
conveying a portion of the ambient sound along an electronic path within the housing from the inlet to the outlet,
wherein, for an operating frequency range, the electronic path is configured to provide a phase difference between the acoustic path and the electronic path of substantially 180 degrees.
16. The method of claim 15 , wherein, for the predetermined frequency range, the phase difference between the acoustic and the electronic path is within 180±10 degrees.
17. The method of claim 15 , wherein, for the predetermined frequency range, the phase difference between the acoustic and the electronic path is within 180±18 degrees.
18. The method of claim 15 , further comprising:
coupling ambient air pressure from the inlet to the outlet along the acoustic path.
19. The method of claim 15 , wherein conveying a portion of the ambient sound along an acoustic path further comprises:
delaying the ambient sound by means of the acoustic delay line.
20. The method of claim 19 , wherein delaying the ambient sound comprises:
conveying the ambient sound through a serpentine tube.
21. The method of claim 19 , wherein delaying the ambient sound comprises:
conveying the ambient sound through a tube filled with a material in which a speed of sound is lower than a speed of sound in air.
22. The method of claim 15 , wherein conveying a portion of the ambient sound along an acoustic path further comprises:
filtering the ambient sound with a passive low-pass filter.
23. The method of claim 22 , where a cutoff frequency of the passive low-pass filter sets an upper limit of the operating frequency range.
24. The method of claim 15 , wherein conveying a portion of the ambient sound along an electronic path further comprises:
a microphone converting a portion of the ambient sound to an ambient audio signal;
processing the ambient audio signal to provide a processed audio signal; and
a speaker converting the processed audio signal to processed sound.
25. The method of claim 24 , further comprising:
combining the sound from the acoustic path and the processed sound in a mixing volume proximate the outlet.
26. The method of claim 25 , wherein the processed sound includes anti-sound to cancel at least a portion of the sound from the acoustic path over the operating frequency range.
27. The method of claim 24 , wherein conveying a portion of the ambient sound along an acoustic path further comprises:
filtering the ambient sound with a passive low-pass filter, wherein
a cutoff frequency of the passive low-pass filter is less than or equal to a resonant frequency of the speaker.
28. The method of claim 15 , wherein:
the housing is an earbud housing configured to fit, at least partially, within and be supported by the ear of the user.