Feedback control

• US 4,494,074 A
• Filed: 04/28/1982
• Issued: 01/15/1985
• Est. Priority Date: 04/28/1982
• Status: Expired due to Term

• Current Assignee: Bose Corporation
• Original Assignee: Bose Corporation
• Inventors: Bose, Amar G.
• Primary Examiner(s): Mullins, James B.
• Assistant Examiner(s): Wan, G.
• Application Number:
  US06/372,472
• Time in Patent Office: 993 Days
• Field of Search: 330/75, 330/85, 330/97, 330/109, 330/294
• US Class Current: 330/109
• CPC Class Codes: G10K 11/17825 Error signals
• CPC Class Codes: G10K 11/17833 by using a self-diagnostic function or a malfunction prevention function, e.g. detecting abnormal output levels
• CPC Class Codes: G10K 11/1785 Methods, e.g. algorithms; Devices G10K11/1781, G10K11/1783 take precedence
• CPC Class Codes: G10K 11/17853 of the filter
• CPC Class Codes: G10K 11/17875 using an error signal without a reference signal, e.g. pure feedback
• 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 2210/108 Communication systems, e.g. where useful sound is kept and noise is cancelled
• 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 2210/3013 Analogue, i.e. using analogue computers or circuits
• CPC Class Codes: G10K 2210/506 Feedback, e.g. howling
• CPC Class Codes: G10K 2210/509 Hybrid, i.e. combining different technologies, e.g. passive and active
• CPC Class Codes: H03F 3/68 Combinations of amplifiers, e.g. multi-channel amplifiers for stereophonics power amplifiers using a combination of several semiconductor amplifiers H03F3/211; combinations of amplifiers using coupling networks with distributed constants H03F3/602
• CPC Class Codes: H03G 3/32 the control being dependent upon ambient noise level or sound level
• 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 5/033 Headphones for stereophonic communication details thereof, e.g. relating to batteries, cables or control elements H04R1/10

Abstract

Headphones have a small cavity between the diaphragm and the ear canal with a microphone in the cavity closely adjacent to the diaphragm providing a feedback signal that is combined with the input electrical signal to be reproduced by the headphones to provide a combined signal that is power amplified for driving the diaphragm.

Claims

1. In a feedback control system for providing a controlled output signal in response to an input control signal having components including amplifying means having an input and output for amplifying a signal applied to said input and arranged in a closed loop with feedback means for coupling said output to said input and the amplifying means characterized by open loop gain and phase margin between said input and output when the feedback path therebetween is interrupted, the improvement comprising,

means for establishing the open loop gain of said amplifying means substantially uniform at a significant level over a predetermined frequency range bounded substantially at at least one end by a break frequency,

said amplifying means including means for establishing the change in said open loop gain as a function of frequency outside said predetermined frequency range in a region from said break frequency to a critical frequency where said open loop gain is substantially unity with magnitude of slope of said open loop gain greater than 6 decibels per octave for a significant portion of said region while maintaining the phase margin in said region sufficient to ensure stability,

thereby providing high gain over said predetermined frequency range while avoiding oscillation and minimizing the error between said controlled output signal and a desired controlled output signal designated by said input control signal.

2. The improvement of claim 1 wherein said phase margin is at least π

/6.

3. The improvement of claims 1 or 2 wherein said amplifying means further includes means for establishing said change in frequency response with said magnitude of slope of said open loop gain being significantly greater than 6 decibels per octave from said break frequency to a first frequency between said break frequency and said critical frequency, less than 12 decibels per octave from said first frequency to a second frequency separated from said first frequency by said critical frequency and substantially zero decibels per octave from said second frequency to a third frequency separated from said critical frequency by said second frequency.

4. The improvement of claim 3 wherein said third frequency is separated from said second frequency by at least an octave.

5. The improvement of claim 3 wherein said magnitude of slope between said cutoff frequency and said first frequency is at least 12 decibels per octave.

6. The improvement of claim 4 wherein said magnitude of slope between said first and second frequencies is no greater than 6 decibels per octave.

7. The improvement of claim 6 wherein said magnitude of slope between said first and second frequencies is substantially 6 decibels per octave.