Active acoustic attenuation system with differential filtering
First Claim
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 attenuation method for attenuating undesirable said output acoustic wave by introducing a cancelling acoustic wave from an output transducer, comprising:
- sensing said input acoustic wave with an input transducer and providing an input signal;
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 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;
bandpass filtering said input signal;
bandpass filtering said error signal to a narrower range than said bandpass filtered input signal.
1 Assignment
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Accused Products
Abstract
An adaptive active acoustic attenuation system is provided with extended frequency range to attenuate undesired noise which was previously filtered out to avoid instability of the adaptive model. The input signal from the input microphone to the model and the error signal from the error microphone to the model are differentially bandpass filtered to provide a narrower frequency range error signal. In one embodiment, the model operates in its stable region to provide accurate well behaved correction signals to the cancelling loudspeaker, while still receiving a low frequency input noise signal from the input microphone including frequencies below such range. Minimum attenuation frequency has been reduced by at least an octave.
80 Citations
36 Claims
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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 attenuation method for attenuating undesirable said output acoustic wave by introducing a cancelling acoustic wave from an output transducer, comprising:
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sensing said input acoustic wave with an input transducer and providing an input signal; 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 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; bandpass filtering said input signal; bandpass filtering said error signal to a narrower range than said bandpass filtered input signal. - View Dependent Claims (2, 3, 4)
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5. 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, comprising:
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sensing said input acoustic wave with an input transducer and providing an input signal; 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 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; highpass filtering said error signal; highpass filtering said input signal to a lower cut-off frequency than said highpass filtered error signal. - View Dependent Claims (6, 7, 8, 9, 10)
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11. 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, comprising:
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sensing said input acoustic wave with an input transducer and providing an input signal; 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 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; highpass filtering said error signal; highpass filtering said input signal to a lower cut-off frequency than said highpass filtered error signal; lowpass filtering said error signal; lowpass filtering said input signal. - View Dependent Claims (12, 13, 14)
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15. 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 system method for attenuating undesirable said output acoustic waves by introducing a cancelling acoustic wave from an output transducer, comprising:
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sensing said input acoustic wave with an input transducer and providing an input signal; sensing the combined said output acoustic waves 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 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; lowpass filtering said input signal; highpass filtering said input signal; lowpass filtering said error signal at one stage; lowpass filtering said error signal at another stage to a lower cut-off frequency than said one stage; highpass filtering said error signal at one stage; highpass filtering said error signal at another stage to a higher cut-off frequency than said one stage highpass filtered error signal; said cut-off frequency of said other stage lowpass filtered error signal being greater than the cut-off frequency of said other stage highpass filtered error signal; the frequency band between said lowpass filtered input signal and said highpass filtered input signal being greater than the frequency band between said other stage lowpass filtered error signal and said other stage highpass filtered error signal. - View Dependent Claims (16, 17, 18)
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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, comprising:
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an input transducer sensing said input acoustic wave and providing an input signal; an error transducer sensing the combined said output acoustic wave and said cancelling acoustic wave from said output transducer and providing an error signal; an adaptive filter model adaptively modeling said acoustic system and 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; a first bandpass filter filtering said input signal; a second bandpass filter filtering said error signal to a narrower range than said bandpass filtered input signal. - View Dependent Claims (20, 21, 22)
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23. 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, comprising:
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an input transducer sensing said input acoustic wave and providing an input signal; an error transducer sensing the combined said output acoustic wave and said cancelling acoustic wave from said output transducer and providing an error signal; an adaptive filter model adaptively modeling said acoustic system and 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; a first highpass filter filtering said error signal; a second highpass filter filtering said input signal to a lower cut-off frequency than said highpass filtered error signal. - View Dependent Claims (24, 25, 26, 27, 28)
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29. 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, comprising:
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an input transducer sensing said input acoustic wave and providing an input signal; an error transducer sensing the combined said output acoustic wave and said cancelling acoustic wave from said output transducer and providing an error signal; an adaptive filter model adaptively modeling said acoustic system and 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; a first highpass filter filtering said error signal; a second highpass filter filtering said input signal to a lower cut-off frequency than said highpass filtered error signal; a first lowpass filter filtering said error signal; a second lowpass filter filtering said input signal. - View Dependent Claims (30, 31, 32)
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33. 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, comprising:
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an input transducer sensing said input acoustic wave and providing an input signal; an error transducer sensing the combined said output acoustic wave and said cancelling acoustic wave from said output transducer and providing an error signal; an adaptive filter model adaptive modeling said acoustic system and 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; a first lowpass filter filtering said input signal; a first highpass filter filtering said input signal; a second lowpass filter filtering said error signal; a third lowpass filter filtering said error signal to a lower cut-off frequency than said second lowpass filter; a second highpass filter filtering said error signal; a third highpass filter filtering said error signal to a higher cut-off frequency than said second highpass filter; the cut-off frequency of said third lowpass filter being greater than the cut-off frequency of said third highpass filter; the frequency band between said first lowpass filter and said first highpass filter being greater than the frequency band between said third lowpass filter and said third highpass filter. - View Dependent Claims (34, 35, 36)
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Specification