Active attenuation of nonlinear sound

In an acoustic system having an input receiving high level input sound and an output radiating an unwanted output sound, an active attenuation method for attenuating said output sound, comprising the steps of:

• sensing said input sound with an input transducer so as to derive therefrom a corresponding electric input signal;
• injecting a canceling sound into said acoustic system by using an output transducer for converting an electric control signal into said canceling sound;
• modeling the transfer characteristic of the input and output transducers;
• modeling the nonlinear propagation of said input sound from said input transducer to the point where said input sound meets said canceling sound by a first nonlinear overall model;
• and
• modeling the nonlinear propagation of said canceling sound from said output transducer to said input transducer by a second nonlinear overall model;
• modeling the nonlinear propagation of said canceling sound from said output transducer to the point where said canceling sound meets said input sound by a third nonlinear overall model;
• and
• separating in each said first, second and third nonlinear overall model a linear system which describes the transmission of a linear part from a nonlinear system which describes the generation of second-order or higher-order nonlinear distortions in said input sound and said canceling sound, whereas both said linear and nonlinear systems are connected in parallel;
• generating said electric control signal from said electric input signal by using a nonlinear filter architecture which is derived from the modeling of the nonlinear sound propagation and from the modeling of the input and output transducers in a manner to compensate for nonlinearities in the acoustic system and to substantially attenuate said output sound through cancellation of said input sound by said canceling sound.

In an acoustic system having an input receiving high level input sound and an output radiating an unwanted output sound, an active acoustic attenuation arrangement for attenuating said output sound, comprising:

• an input transducer sensing said input sound and providing therefrom an electric input signal;
• an output transducer driven by an electric control signal and injecting a canceling sound into said acoustic system;
• and
• a nonlinear controller, having an sensing input supplied with said electric input signal and a controller output connected with said output transducer, whereas said electric control signal is derived from said electric input signal by simulating the nonlinear sound propagation in the acoustic system and by compensating for the linear or nonlinear transfer behavior of said input and output transducers to substantially attenuate said output sound through cancellation of said input sound by said canceling sound;
• wherein said nonlinear controller comprises:
• a nonlinear filter having a downstream input and a downstream output for modeling the nonlinear propagation of said input sound and having an upstream input and an upstream output for modeling the nonlinear propagation of a feedback sound radiated by said output transducer in upstream direction;
• an inverter having an input connected to said downstream output and having an inverter output connected with said upstream input for providing an 180.degree. phase shifted input signal;
• an output filter having an input connected to the output of said inverter, having an output connected with said controller output and having a transfer characteristic between the input and output of said output filter such that the signal at the output of said inverter is equal to said cancelling sound in the acoustic system;
• an input filter having an input connected to said sensing input and an output, the transfer characteristic between the input and output of said input filter being adjusted such that the signal at the output of said input filter is equal to the sum of said input sound and said feedback sound;
• and
• a summer having a noninverting input connected to the output of said input filter, an inverting input connected to the upstream output of the nonlinear filter and an output for providing said input sound to the downstream input of said nonlinear filter.

In an acoustic system having an input receiving high level input sound and an output radiating an unwanted output sound, an active acoustic attenuation arrangement for attenuating said output sound, comprising:

• an input transducer sensing said input sound and providing therefrom an electric input signal;
• an output transducer driven by an electric control signal and injecting a canceling sound into said acoustic system;
• and
• a nonlinear controller, having an sensing input supplied with said electric input signal and a controller output connected with said output transducer, whereas said electric control signal is derived from said electric input signal by simulating the nonlinear sound propagation in the acoustic system and by compensating for the linear or nonlinear transfer behavior of said input and output transducers to substantially attenuate said output sound through cancellation of said input sound by said canceling sound;
• wherein said nonlinear controller comprises:
• a summer having a first input connected with said sensing input of said nonlinear controller, a second input and an output providing the sum of the signals at the first and second input;
• a downstream filter having an input connected with the output of said summer and an output connected to said controller output for modeling the nonlinear propagation of said input sound;
• and
• an upstream filter having an input connected with said controller output and an output connected to the second input of said summer for modeling the nonlinear propagation of said canceling sound in said acoustic system.

In an acoustic system having an input receiving high level input sound and an output radiating an unwanted output sound, an active acoustic attenuation arrangement for attenuating said output sound, comprising:

• an input transducer sensing said input sound and providing therefrom an electric input signal;
• an output transducer driven by an electric control signal and injecting a canceling sound into said acoustic system;
• and
• a nonlinear controller, having an sensing input supplied with said electric input signal and a controller output connected with said output transducer, whereas said electric control signal is derived from said electric input signal by simulating the nonlinear sound propagation in the acoustic system and by compensating for the linear or nonlinear transfer behavior of said input and output transducers to substantially attenuate said output sound through cancellation of said input sound by said canceling sound;
• wherein said nonlinear controller comprises:
• a summer having a first input, a second input and an output connected to said controller output providing the sum of the signals at the first and second input;
• a first filter having an filter input connected with said sensing input of said nonlinear controller and an filter output connected with the first input of said summer forming a feed-forward path;
• and
• a second filter having an filter input connected with the output of said summer and an filter output connected to the second input of said summer forming a feedback path, either said first filter or said second filter or both said first filter and said second filter have a nonlinear transfer characteristic between the filter input and the filter output.

In an acoustic system having an input receiving high level input sound and an output radiating an unwanted output sound, an active acoustic attenuation arrangement for attenuating said output sound, comprising:

• an input transducer sensing said input sound and providing therefrom an electric input signal;
• an output transducer driven by an electric control signal and injecting a canceling sound into said acoustic system;
• and
• a nonlinear controller, having an sensing input supplied with said electric input signal and a controller output connected with said output transducer, whereas said electric control signal is derived from said electric input signal by simulating the nonlinear sound propagation in the acoustic system and by compensating for the linear or nonlinear transfer behavior of said input and output transducers to substantially attenuate said output sound through cancellation of said input sound by said canceling sound;
• wherein said nonlinear controller comprises:
• a feed-forward tapped delay line, comprising a plurality of n delay elements connected in series, having an input connected to said sensing input and providing a set of n+1 progressively delayed signal outputs;
• a feedback tapped delay line, comprising a plurality of m delay elements connected in series, having an input connected to said controller output and providing a set of m+1 progressively delayed signal outputs;
• and
• a neural network having a plurality of m+n+2 inputs connected respectively to the signal outputs of said feed-forward tapped delay line and said feedback tapped delay line, having an output connected to said controller output.