Reducing Occlusion Effect in ANR Headphones

• US 20140126735A1
• Filed: 11/02/2012
• Published: 05/08/2014
• Est. Priority Date: 11/02/2012
• Status: Active Grant

• Current Assignee: Bose Corporation
• Original Assignee: Daniel M. Gauger Jr
• Inventors: Gauger, Daniel M. Jr.
• Granted Patent: US 9,020,160 B2
• Time in Patent Office: Days
• US Class Current: 381/71.6
• CPC Class Codes: G10K 11/17823 Reference signals, e.g. ambient acoustic environment
• CPC Class Codes: G10K 11/17825 Error signals
• CPC Class Codes: G10K 11/17837 by retaining part of the ambient acoustic environment, e.g. speech or alarm signals that the user needs to hear
• CPC Class Codes: G10K 11/17861 using additional means for damping sound, e.g. using sound absorbing panels
• CPC Class Codes: G10K 11/17881 the reference signal being an acoustic signal, e.g. recorded with a microphone
• CPC Class Codes: G10K 11/17885 additionally using a desired external signal, e.g. pass-through audio such as music or speech
• CPC Class Codes: G10K 2210/1081 Earphones, e.g. for telephones, ear protectors or headsets
• CPC Class Codes: G10K 2210/3026 Feedback
• CPC Class Codes: G10K 2210/3027 Feedforward
• CPC Class Codes: G10K 2210/3056 Variable gain
• CPC Class Codes: H04R 1/1008 Earpieces of the supra-aural or circum-aural type
• CPC Class Codes: H04R 1/1083 Reduction of ambient noise active noise reduction per se G10K11/175; protective devices for the ear, e.g. providing acoustic protection A61F11/06
• CPC Class Codes: H04R 2460/05 Electronic compensation of the occlusion effect

Abstract

In an active noise reducing headphone, a signal processor is configured to apply first feedback filters to the feedback signal path, causing the feedback signal path to operate at a first gain level, as a function of frequency, during a first operating mode, and apply second feedback filters to the feedback signal path, causing the feedback signal path to operate at a second gain level less than the first gain level at some frequencies during a second operating mode. The first gain level is a level of gain that results in effective cancellation of sounds transmitted through or around the ear cup and through the user'"'"'s head, and the second level is a level of gain that is matched to the level of sound of a typical wearer'"'"'s voice transmitted through the wearer'"'"'s head when wearing the headphone.

Claims

1. An active noise reducing headphone comprising:

an ear piece configured to couple to a wearer'"'"'s ear to define an acoustic volume comprising the volume of air within the wearer'"'"'s ear canal and a volume within the ear piece;

a feedback microphone acoustically coupled to the acoustic volume and electrically coupled to a feedback active noise cancellation signal path;

an output transducer acoustically coupled to the acoustic volume via the first volume and electrically coupled to the feedback signal path; and

a signal processor configured to apply filters and control gains of the feedback signal path;

wherein the signal processor is configured to;

apply first feedback filters to the feedback signal path, the first feedback filters causing the feedback signal path to operate at a first gain level, as a function of frequency, during a first operating mode, and

apply second feedback filters to the feedback signal path, the second feedback filters causing the feedback signal path to operate at a second gain level less than the first gain level at some frequencies during a second operating mode,

the first gain level being a level of gain that results in effective cancellation of sounds transmitted through or around the ear piece and through the user'"'"'s head into the acoustic volume when the ear piece is coupled to the wearer'"'"'s ear, and

the second level being a level of gain that is matched to the level of sound of a typical wearer'"'"'s voice transmitted through the wearer'"'"'s head when the ear piece is coupled to the wearer'"'"'s ear.

2. The headphone of claim 1, further comprising a feed-forward microphone acoustically coupled to an external environment and electrically coupled to a feed-forward active noise cancellation signal path;

wherein;

the output transducer is electrically coupled to the feed-forward signal path;

the signal processor is further configured to apply filters and control gains of the feed-forward signal path;

in the first operating mode the signal processor is configured to apply first feed-forward filters to the feed-forward signal path in conjunction with applying the first feedback filters to the feedback signal path to achieve effective cancellation of ambient sound; and

in the second operating mode, the signal processor is configured to apply second feed-forward filters to the feed-forward signal path, the second filters being selected to provide active hear-through of ambient sounds with ambient naturalness.

3. The headphone of claim 2, wherein the second feedback filters and the second feed-forward filters are selected to provide active hear-through of a user'"'"'s own voice with self-naturalness.

4. The headphone of claim 2, wherein the second feed-forward filters applied to the feed-forward path is a non-minimum phase response.

5. The headphone of claim 1, wherein the sound of the typical wearer'"'"'s voice below a first frequency passively transmitted through the wearer'"'"'s head is amplified when the ear piece is coupled to the wearer'"'"'s ear, and sound above the first frequency is attenuated when the ear piece is so coupled, and the feedback signal path is operative over a frequency range extending higher than the first frequency.

6. The headphone of claim 1, wherein the signal processor is a first signal processor and the feedback signal path is a first feedback signal path, the headphone further comprising:

a second ear piece configured to couple to a wearer'"'"'s second ear to define a second acoustic volume comprising the volume of air within the wearer'"'"'s second ear canal and a volume within the second ear piece;

a second feedback microphone acoustically coupled to the second acoustic volume and electrically coupled to a second feedback active noise cancellation signal path;

a second output transducer acoustically coupled to the second acoustic volume via the volume within the second ear piece and electrically coupled to both the second feedback active noise cancellation signal path; and

a second signal processor configured to apply filters and control gains of the second feedback active noise cancellation signal path;

wherein the second signal processor is configured to;

apply third feedback filters to the second feedback signal path, the second feedback filters causing the second feedback signal path to operate at the first gain level during the first operating mode of the first signal processor, and

apply fourth feedback filters to the second feedback signal path to operate at the second gain level during the second operating mode of the first signal processor.

7. The headphone of claim 6, wherein the first and second signal processors are portions of a single signal processing device.

8. The headphone of claim 6, wherein the third feedback filters are not identical to the first feedback filters.

9. A method of configuring an active noise reducing headphone comprising

an ear piece configured to couple to a wearer'"'"'s ear to define an acoustic volume comprising the volume of air within the wearer'"'"'s ear canal and a volume within the ear piece;

a feed-forward microphone acoustically coupled to an external environment and electrically coupled to a feed-forward active noise cancellation signal path;

a feedback microphone acoustically coupled to the acoustic volume and electrically coupled to a feedback active noise cancellation signal path;

an output transducer acoustically coupled to the acoustic volume via the volume within the ear piece and electrically coupled to both the feed-forward and feedback active noise cancellation signal paths; and

a signal processor configured to apply filters and control gains of both the feed-forward and feedback active noise cancellation signal paths,

the method comprising;

for at least one frequency, measuring the ratio

10. The method of claim 9, further comprising iterating the steps of selecting K_on and K_ht, applying the selected filters, and measuring the ratio

11. The method of claim 9, wherein selecting the filter for the feed-forward signal path comprises:

selecting a value of K_ht that causes the formula