Active attenuation system with on-line modeling of speaker, error path and feedback pack

• US 4,677,676 A
• Filed: 02/11/1986
• Issued: 06/30/1987
• Est. Priority Date: 02/11/1986
• Status: Expired due to Term

• Current Assignee: Nelson Industries Incorporated (Cummins Incorporated)
• Original Assignee: Nelson Industries Incorporated (Cummins Incorporated)
• Inventors: Eriksson, Larry J.
• Primary Examiner(s): Rubinson, Gene Z.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/828,454
• Time in Patent Office: 504 Days
• Field of Search: 381/71, 381/73, 381/94
• US Class Current: 381/71.11
• CPC Class Codes: G10K 11/17817 between the output signals and the error signals, i.e. secondary path
• CPC Class Codes: G10K 11/17819 between the output signals and the reference signals, e.g. to prevent howling
• CPC Class Codes: G10K 11/1785 Methods, e.g. algorithms; Devices G10K11/1781, G10K11/1783 take precedence
• 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 11/17881 the reference signal being an acoustic signal, e.g. recorded with a microphone
• CPC Class Codes: G10K 2210/3017 Copy, i.e. whereby an estimated transfer function in one functional block is copied to another block
• CPC Class Codes: G10K 2210/30232 Transfer functions, e.g. impulse response
• CPC Class Codes: G10K 2210/3045 Multiple acoustic inputs, single acoustic output
• CPC Class Codes: G10K 2210/3049 Random noise used, e.g. in model identification
• CPC Class Codes: G10K 2210/32272 Helmholtz resonators
• CPC Class Codes: G10K 2210/511 Narrow band, e.g. implementations for single frequency cancellation
• CPC Class Codes: G10K 2210/512 Wide band, e.g. non-recurring signals

Abstract

An active acoustic attenuation system is provided that actively models direct and feedback paths as well as characteristics of the secondary cancelling sound source and the error path on an on-line basis. The primary model uses a recursive least mean squares RLMS algorithm that is excited by the input acoustic noise and uses the residual acoustic noise as an error signal. The secondary sound source or cancelling speaker and the error path are modeled by a second algorithm, particularly an LMS algorithm, that uses an additional auxiliary low level, random, uncorrelated noise source as an input signal. The resulting overall system provides excellent attenuation of narrow band and broad band noise over a relatively wide frequency range on a completely adaptive basis without directional transducers.

Claims

1. In an acoustic system having an input for receiving an input acoustic wave and an output for radiating an output acoustic wave, an active attenutation method for attenuating undesirable said output acoustic wave by introducing a cancelling acoustic wave from an output transducer, comprising:

sensing the combined said output acoustic wave and said cancelling acoustic wave from said output transducer with an error transducer and providing an error signal;

modeling said acoustic system with an adaptive filter model having an error input from said error transducer and outputting a correction signal to said output transducer to introduce the cancelling acoustic wave such that said error signal approaches a given value;

providing an auxiliary noise source and introducing noise therefrom into said model, such that said error transducer also senses the auxiliary noise from said auxiliary noise source.

2. The invention according to claim 1 comprising introducing noise from said auxiliary noise source which is random and uncorrelated to said input acoustic wave.

3. The invention according to claim 2 comprising modeling said output transducer on-line with a second adaptive filter model having a model input from said auxiliary noise source, and providing a copy of said second adaptive filter model in said first mentioned adaptive filter model to compensate for said output transducer.

4. The invention according to claim 3 comprising summing the outputs of said error transducer and said second adaptive filter model and using the result as an error input to said second adaptive filter model, and summing the outputs of said auxiliary noise source and said first adaptive filter model and using the result as said correction signal to said output transducer.

5. The invention according to claim 2 wherein said error transducer is spaced from said output transducer along an error path, and comprising modeling said error path on-line with a second adaptive filter model having a model input from said auxiliary noise source, and providing a copy of said second adaptive filter model in said first mentioned adaptive filter model to compensate for said error path.

6. The invention according to claim 5 comorising summing the outputs of said error path and said second adaptive filter model and using the result as an error input to said second adaptive filter model, and summing the outputs of said auxiliary noise source and said first adaptive filter model and using the result as said correction signal to said output transducer.

7. The invention according to claim 2 wherein said error transducer is spaced from said output transducer along an error path, and comprising modelling both said error path and said output transducer on-line with a second adaptive filter model having a model input from said auxiliary noise source, and providing a copy of said second adaptive filter model in said first mentioned adaptive filter model to compensate for said output transducer and said error path.

8. The invention according to claim 7 comprising:

summing the outputs of said error path and said second adaptive filter model and using the result as an error input to said second adaptive filter model;

summing the outputs of said auxiliary noise source and said first adaptive filter model and using the result as said correction signal to said output transducer.

9. In an acoustic system having an input for receiving an input acoustic wave and an output for radiating an output acoustic wave, an active attenuation method for attenuating undesirable said output acoustic wave by introducing a cancelling acoustic wave from an output transducer, and for adaptively compensating for feedback to said input from said output transducer for both broad band and narrow band acoustic waves on-line without off-line pre-training, and providing both adaptive error path compensation and adaptive compensation of said output transducer on-line without off-line pre-training, comprising:

sensing said input acoustic wave with an input transducer;

sensing the combined said output acoustic wave and said cancelling acoustic wave from said output transducer with an error transducer spaced from said output transducer along an error path and providing an error signal;

modeling said acoustic system with an adaptive filter model having a model input from said input transducer and an error input from said error transducer and outputting a correction signal to said output transducer to introduce the cancelling acoustic wave such that said error signal approaches a given value;

modeling the feedback path from said output transducer to said input transducer with the same said model by modeling said feedback path as part of said model such that the latter adaptively models both said acoustic system and said feedback path, without separate modeling of said acoustic system and said feedback path, and without a separate model pre-trained off-line solely to said feedback path;

providing an auxiliary noise source and introducing noise therefrom into said model, such that said error transducer also senses the auxiliary noise from said auxiliary noise source;

modeling both said error path and said output transducer on-line with a second adaptive filter model, and providing a copy of said second adaptive filter model in said first mentioned adaptive filter model to compensate for said output transducer and said error path.

10. The invention according to claim 9 comprising providing said second adaptive filter model having a model input from said auxiliary noise source.

11. The invention according to claim 10 comprising summing the outputs of said error path and said second adaptive filter model and using the result as an error input to said second adaptive filter model.

12. The invention according to claim 11 comprising summing the outputs of said auxiliary noise source and said first adaptive filter model and using the result as said correction signal to said output transducer.

13. The invention according to claim 12 comprising providing said first adaptive filter model with first and second algorithm means each having an error input from said error transducer, summing the outputs of said first and second algorithm means and then summing the result thereof with said auxiliary noise from said auxiliary noise source and using the result as said correction signal to said output transducer, and providing a copy of said second adaptive filter model in each of said first and second algorithm means.

14. The invention according to claim 13 comprising providing a first copy of said second adaptive filter model of said error path and said output transducer, providing an input to said first algorithm means from said input transducer, providing an input to said first copy from said input transducer, multiplying the output of said first copy with said error signal and using the result as a weight update signal to said first algorithm means, providing a second copy of said second adaptive filter model of said error path and said output transducer, providing an input to said second algorithm means from said correction signal, providing an input to said second copy from said correction signal, multiplying the output of said second copy with said error signal and using the result as a weight update signal to said second algorithm means.

15. The invention according to claim 11 comprising providing said second adaptive filter model with algorithm means, summing the outputs of said algorithm means and said error path and multiplying the sum with said auxiliary noise from said auxiliary noise source and using the result as a weight update signal to said algorithm means.

16. In an acoustic system having an input for receiving an input acoustic wave and an output for radiating an output acoustic wave, active attentuation apparatus for attenuating undesirable said output acoustic wave by introducing a cancelling acoustic wave from an output transducer, comprising:

an error transducer sensing the combined said output acoustic wave and said acoustic wave from said output transducer and providing an error signal;

an adaptive filter model adaptively modeling said acoustic system on-line and having an error input from said error transducer and outputting a correction signal to said output transducer to introduce said cancelling acoustic wave such that said error signal approaches a given value;

an auxiliary noise source introducing auxiliary noise into said adaptive filter model which is random and uncorrelated with said input acoustic wave; and

a second adaptive filter model having a model input from said auxiliary noise source and an error input from said error transducer.

17. The invention acccording to claim 16 comprising summer means summing auxiliary noise from said auxiliary noise source with the output of said first adaptive filter model and supplying the result as said correction signal to said output transducer.

18. The invention according to claim 17 wherein said second adaptive filter model comprises algorithm means, and comprising second summer means summing the outputs of said error transducer and said algorithm means, and comprising multiplier means multiplying the output of said second summer means with said auxiliary noise from said auxiliary noise source and supplying the result as a weight update signal to said algorithm means.

19. In an acoustic system having an input for receiving an input acoustic wave and an output for radiating an output acoustic wave, active attenuation apparatus for attenuating undesirable said output acoustic wave by introducing a cancelling acoustic wave from an output transducer, and for adaptively compensating for feedback to said input from said output transducer for both broad band and narrow band acoustic waves on-line without off-line pre-training and for providing both adaptive error path compensation and adaptive compensation of said output transducer on-line without off-line ore-training, comprising:

an input transducer for sensing said input acoustic wave;

an error transducer spaced from said output transducer along an error path and sensing the combined said output acoustic wave and said acoustic wave from said output transducer and providing an error signal;

a first adaptive filter model adaptively modeling said acoustic system on-line without dedicated off-line pre-training, and also modeling the feedback path from said output transducer to said input transducer on-line without dedicated off-line pre-training, said first adaptive filter model having a model input from said input transducer and an error input from said error transducer and outputting a correction signal to said output transducer to introduce said cancelling acoustic wave such that said error signal approaches a given value;

an auxiliary noise source introducing auxiliary noise into said adaptive filter model;

a second adaptive filter model adaptively modeling both said error path and said output transducer on-line without dedicated off-line pre-training; and

a copy of said second adaptive filter model in said first adaptive filter model to compensate for both said error path and said output transducer adaptively on-line.

20. The invention according to claim 19 wherein said second adaptive filter model has a model input from said auxiliary noise source.

21. The invention according to claim 20 comprising summer means summing the outputs of said error path and said second adaptive filter model and outputting the result as an error input to said second adaptive filter model.

22. The invention according to claim 21 wherein said second adaptive filter model comprises algorithm means, and comprising multiplier means multiplying the output of said summer means with said auxiliary noise from said auxiliary noise source and supplying the result as a weight update signal to said algorithm means.

23. The invention according to claim 21 comprising second summer means summing auxiliary noise from said auxiliary noise source with the output of said first adaptive filter model and supplying the result as said correction signal to said output transducer.

24. The invention according to claim 23 wherein said first adapative filter model comprises first and second algorithm means each having an error input from said error transducer, and comprising third summer means summing the outputs of said first and second algorithm means and using the result as an input to said second summer means for summing with said auxiliary noise, and comprising a first copy of said second adaptive filter model of said error path and said output transducer in said first algorithm means, and comprising a second copy of said second adaptive filter model of said error path and said output transducer in said second algorithm means.

25. The invention according to claim 24 wherein said first algorithm means has an input from said input transducer, said first copy of said second adaptive filter model has an input from said input transducer, and comprising first multiplier means multiplying the output of said first copy with said error signal and using the result as a weight update signal to said first algorithm means, and wherein said second algorithm means has an input from said correction signal, said second copy of said second adaptive filter model has an input from said correction signal, and comprising second multiplier means multiplying the output of said second copy with said error signal and using the result as a weight update signal to said second algorithm means.