ACTIVE NOISE REDUCTION SYSTEM

• US 20110206214A1
• Filed: 02/25/2011
• Published: 08/25/2011
• Est. Priority Date: 02/25/2010
• Status: Active Grant

• Current Assignee: Harman Becker Automotive Systems GmbH (Samsung Electronics Co. Ltd.)
• Original Assignee: Harman Becker Automotive Systems GmbH (Samsung Electronics Co. Ltd.)
• Inventors: Wurm, Michael, Perkmann, Michael, Christoph, Markus
• Granted Patent: US 8,903,101 B2
• Time in Patent Office: Days
• US Class Current: 381/71.6
• CPC Class Codes: G10K 11/17813 characterised by the analysis of the acoustic paths, e.g. estimating, calibrating or testing of transfer functions or cross-terms
• CPC Class Codes: G10K 11/17854 the filter being an adaptive filter
• CPC Class Codes: G10K 11/17857 Geometric disposition, e.g. placement of microphones
• CPC Class Codes: G10K 11/17873 using a reference signal without an error signal, e.g. pure feedforward
• 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 2210/3055 Transfer function of the acoustic system

Abstract

A system for actively reducing noise at a listening point, includes an earphone housing, a transmitting transducer, a receiving transducer and a controller. The transmitting transducer converts a first electric signal into a first acoustic signal, and radiates the first acoustic signal along a first acoustic path having a first transfer characteristic and along a second acoustic path having a second transfer characteristic. The receiving transducer converts the first acoustic signal and ambient noise into a second electrical signal. The controller compensates for the ambient noise by providing a noise reducing electrical signal to the transmitting transducer. The noise reducing electrical signal is derived from a filtered electrical signal that is provided by filtering the second electrical signal with a third transfer characteristic. The second and the third transfer characteristics together model the first transfer characteristic.

Claims

1. An active noise reduction system, comprising:

an earphone to be acoustically coupled to an ear of a user, the earphone comprising

a cupped housing having an aperture;

a transmitting transducer that converts a first electrical signal into a first acoustical signal, and that radiates the first acoustical signal to the ear, where the transmitting transducer is arranged at the aperture of the cupped housing thereby defining an earphone cavity; and

a receiving transducer that converts a second acoustical signal into a second electrical signal, where the receiving transducer is arranged within the earphone cavity;

a first acoustical path that extends from the transmitting transducer to the ear, and that has a first transfer characteristic;

a second acoustical path that extends from the transmitting transducer to the receiving transducer, and that has a second transfer characteristic; and

a control unit electrically connected to the receiving transducer and the transmitting transducer, and that compensates for ambient noise by generating a noise reducing electrical signal that is supplied to the transmitting transducer;

where the noise reducing electrical signal is derived from a filtered electrical signal, which is provided by filtering the second electrical signal with a third transfer characteristic; and

where the second and the third transfer characteristics together model the first transfer characteristic.

2. The system of claim 1, where the noise reducing electrical signal and the ambient noise signal have substantially equal amplitudes, and where phase of the noise reducing electrical signal is substantially opposite to phase of the ambient noise signal.

3. The system of claim 1, further comprising a signal source that provides a source signal, where the first electrical signal is derived from the source signal and the noise reducing electrical signal.

4. The system of claim 3, where the control unit comprises a first filter that provides a first filtered signal, and that has a fourth transfer characteristic that is substantially inverse to the first transfer characteristic.

5. The system of claim 4, where the control unit further comprises a second filter that provides a second filtered signal, and that has a fifth transfer characteristic that is substantially equal to the second transfer characteristic.

6. The system of claim 5, where the control unit further comprises:

a subtracting unit connected to the first filter and the signal source, where the subtracting unit subtracts the first filtered signal from the source signal to generate the first electrical signal, and where first electrical signal is inverted and supplied to the second filter; and

a summing unit connected to the second filter and the receiving transducer, where the summing unit adds the second filtered signal to the second electrical signal to generate an electrical noise signal that is supplied to the first filter.

7. The system of claim 5, where at least one of the first and second filters is an adaptive filter.

8. The system of claim 1, where the control unit comprises at least one of analog and digital circuitry.

9. The system of claim 1, where the transmitting transducer is mounted to a hermetically sealed volume.

10. The system of claim 9, where the transmitting transducer is hermetically mounted to the housing to form the hermetically sealed volume.

11. A system for actively reducing noise at a listening point, comprising:

an earphone housing having an earphone aperture and an inner earphone cavity;

a transmitting transducer positioned at the earphone aperture, where the transmitting transducer converts a first electric signal into a first acoustic signal, and radiates the first acoustic signal along a first acoustic path having a first transfer characteristic and along a second acoustic path having a second transfer characteristic;

a receiving transducer positioned within the earphone cavity, where the receiving transducer converts the first acoustic signal and ambient noise into a second electrical signal; and

a controller that compensates for the ambient noise by providing a noise reducing electrical signal to the transmitting transducer, where the noise reducing electrical signal is derived from a filtered electrical signal that is provided by filtering the second electrical signal with a third transfer characteristic;

where the first acoustic path extends from the transmitting transducer to the listening point, where the second acoustic path extends from the transmitting transducer to the receiving transducer, and where the second and the third transfer characteristics together model the first transfer characteristic.

12. The system of claim 11, where the noise reducing electrical signal and the ambient noise have substantially equal amplitudes, and where phase of the noise reducing electrical signal is substantially opposite to phase of the ambient noise.

13. The system of claim 11, further comprising a signal source that provides a source signal, where the first electrical signal is derived from the source signal and the noise reducing electrical signal.

14. The system of claim 13, where the controller comprises a first filter having a fourth transfer characteristic that is substantially inverse to the first transfer characteristic, where the first filter filters a third electric signal derived from the filtered electric signal to provide a first filtered signal, and where the first electrical signal is derived from the first filtered signal.

15. The system of claim 14, where the controller further comprises a second filter having a fifth transfer characteristic that is substantially equal to the second transfer characteristic, where the second filter filters the first electrical signal to provide a second filtered signal, and where the third electric signal is derived from the second filtered signal.

16. The system of claim 15, where the controller further comprises:

a subtractor connected to the first filter and the signal source, where the subtractor subtracts the first filtered signal from the source signal to generate the first electrical signal, and where first electrical signal is inverted and supplied to the second filter; and

an adder connected to the second filter and the receiving transducer, where the adder adds the second filtered signal to second electrical signal to generate an electrical noise signal that is supplied to the first filter.

17. The system of claim 15, where at least one of the first and second filters is an adaptive filter.

18. The system of claim 11, where the transmitting transducer is mounted to a hermetically sealed volume.

19. The system of claim 18, where the transmitting transducer is hermetically mounted to the housing to form the hermetically sealed volume.