Ear defenders employing active noise control

• US 5,600,729 A
• Filed: 08/22/1995
• Issued: 02/04/1997
• Est. Priority Date: 01/28/1993
• Status: Expired due to Term

• Current Assignee: Qinetiq Limited (QinetiQ Group PLC)
• Original Assignee: The secretary of state for defence in her Britannic Majesty's Government of the United Kingdom of Great Britain And Northern Ireland
• Inventors: Darlington, Paul, Powell, Gerald A.
• Primary Examiner(s): Isen, Forester W.
• Application Number:
  US08/495,661
• Time in Patent Office: 532 Days
• Field of Search: 381/71, 381/72, 381/74, 381/25
• US Class Current: 381/71.6
• CPC Class Codes: A61F 11/145 electric, e.g. for active noise reduction
• 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 11/17875 using an error signal without a reference signal, e.g. pure feedback
• CPC Class Codes: G10K 2210/1081 Earphones, e.g. for telephones, ear protectors or headsets
• CPC Class Codes: G10K 2210/3011 Single acoustic input
• CPC Class Codes: G10K 2210/30232 Transfer functions, e.g. impulse response
• CPC Class Codes: G10K 2210/506 Feedback, e.g. howling

Abstract

An ear defender having one or more microphones (1) for detecting the sound level in the proximity of the wearer'"'"'s ear, one or more speakers (4) for generating a noise reduction signal within the earshell, and a digital feedback controller (W) for generating a feedback signal derived from the output of the microphones and for applying said feedback signal to the speaker inputs, and estimation means (F'"'"') for providing an estimation of the earshell transfer function and subtracting from the input to the feedback controller a signal representing the estimated electroacoustic transfer function of the system. The operation of the digital feedback controller may be controllable by the output of a computational circuit (C) operable on the difference between the microphone output and the feedback controller input modified by a model (F") of the electroacoustic transfer function. A second, analogue or digital, feedback controller (W'"'"') may be included to provide an approximate feedback signal to the speakers and to improve the impulse response of the system.

Claims

1. An ear defender comprising an earshell, detector means (1) for detecting the sound level in the proximity of the wearer'"'"'s ear, output means (4) for generating a noise reduction signal wig the earshell, and a digital feedback controller (W) for generating a feedback signal derived from the output of said detector means and for applying said feedback signal to the input of the output means, characterised by estimation means (F'"'"') for providing an estimation of the earshell transfer function and subtracting from the input to the feedback controller a signal representing the estimated electroacoustic transfer function of the system, and a second feedback controller (W'"'"') for providing active noise control on the basis of an average configuration for the system.

2. An ear defender according to claim 1 including means for determining the configuration and operation of the feedback controller (W) and the estimation means (F'"'"') when the system is activated or on other known occasions.

3. An ear defender according to claim 1 in which the second feedback controller (W) operates by analogue means.

4. An ear defender according to claim 1 including means for modifying the action of the first feedback controller (W) to reflect variations in the electroacoustic transfer function of the earshell.

5. An ear defender according to claim 4 in which the means for modifying the action of the first feedback controller (W) comprises a computational circuit operating on the difference between the output of the detector means and the output of an additional controller (F") which consists of the sum of a model of the electroacoustic transfer function and the input of the fast feedback controller.

6. An ear defender according to claim 5 in which the computational circuit operates on the said difference by means of an LMS algorithm.

7. An ear defender according to claim 1 in which the detector means comprise one or more microphones.

8. An ear defender according to claim 1 in which the output means for generating a noise reduction signal comprise one or more loudspeakers.

9. An ear defender according to claim 1 including means for communicating aural information to the wearer, said means being applied to the input of the output means for generating a noise reduction signal.

10. An ear defender according to claim 1 including means for controlling the operation of the fast feedback controller and the estimating means in accordance with the nature of the ambient noise.