Active control of sound and vibration

1. An apparatus for active cancellation of sound and vibration, the apparatus comprising

a padding ( 170 ) and sound and vibration generation means ( 110 ) for jointly producing vibration and sound under control of a driving signal (d) provided as input thereto, said sound and vibration generation means ( 110 ) arranged inside the padding ( 170 ) to generate mechanical vibration that is perceivable as a vibration and sound on at least one outer surface ( 172 ) of the padding ( 170 ) and to radiate a sound through said at least one outer surface ( 172 ) of the padding ( 170 );

feedback means ( 130 ) for providing feedback information (f) that is indicative of acoustic energy of sound and vibration inside the padding ( 170 ); and

driving means ( 150 ) for generating the driving signal (d) in dependence of said feedback information (f) so as to reduce energy of ambient sound and vibration induced inside the padding ( 170 ) due to one or more external sources of sound and vibration,

wherein the feedback means ( 130 ) comprises

a first sensor arranged to provide a first feedback signal (f 1 ) that is descriptive of acoustic kinetic energy within the padding ( 170 ), and

a second sensor arranged to provide a second feedback signal (f 2 ) that is descriptive of acoustic potential energy within the padding ( 170 ); and

the feedback information (f) comprises said first and second feedback signals (f 1 , f 2 ).

2. An apparatus according to claim 1 , wherein

the first sensor comprises an accelerometer ( 132 ) arranged to provide the first feedback signal (f 1 ) that is descriptive of a velocity of movement within the padding ( 170 ); and

the second sensor comprises a pressure sensor ( 134 ) arranged to provide the second feedback signal (f 2 ) that is descriptive of a sound pressure within the padding ( 170 ).

3. An apparatus according to claim 1 , wherein the driving means ( 150 ) is arranged to

derive a first cancellation signal by multiplying the first feedback signal (f 1 ) by a first adaptable gain value (g 1 );

derive a second cancellation signal by multiplying the second feedback signal (f 2 ) by a second adaptable gain value (g 2 ); and

generate the driving signal (d) as a signal that includes a combination of the first and second cancellation signals.

4. An apparatus according to claim 3 , wherein the driving means ( 150 ) is arranged to generate the driving signal (d) as the sum of the first and second cancellation signals.

5. An apparatus according to claim 3 , wherein the driving means ( 150 ) is arranged to

receive an input audio signal (s) for reproduction by the sound and vibration generation means ( 110 ); and

generate the driving signal (d) as the sum of said input audio signal (s), the first cancellation signal and the second cancellation signal.

6. An apparatus according to claim 3 , further comprising an adaptation means ( 152 ) arranged to carry out one of the following:

derive respective values of the first and second adaptable gains (g 1 , g 2 ) such that the energy of the driving signal (d) is minimized, thereby reducing both the kinetic energy and the potential energy of ambient sound and vibration induced inside the padding ( 170 );

set the value of the first adaptable gain (g 1 ) to zero and derive the value of the second adaptable gain (g 2 ) such that the energy of the driving signal (d) is minimized, thereby reducing the potential energy of ambient sound and vibration induced inside the padding ( 170 );

set the value of the second adaptable gain (g 2 ) to zero and derive the value of the first adaptable gain (g 1 ) such that the energy of the driving signal (d) is minimized, thereby reducing the kinetic energy of ambient sound and vibration induced inside the padding ( 170 ).

7. An apparatus according to claim 3 , wherein the driving means ( 150 ) is arranged to

process the first feedback signal (f 1 ) by a first compensation filter (H 1 ) that is arranged to model an inverse of a first transfer function from the driving signal (d) to the first feedback signal (f 1 ); and

process the second feedback signal by a second compensation filter (H 2 ) that is arranged to model an inverse a second transfer function from the driving signal (d) to the second feedback signal (f 2 ).

8. An apparatus according to claim 7 , further comprising an adaptation means ( 152 ) arranged to carry out a filter calibration procedure to determine said first and second transfer functions (H 1 , H 2 ), the filter calibration procedure comprising

providing a predefined calibration signal as the driving signal (d) as input to the sound and vibration generation means ( 110 ) to generate corresponding first and second feedback signals (f 1 , f 2 ), and

deriving first and second sets of filter coefficients that, respectively, estimate the first and second transfer functions.

9. An apparatus according to claim 8 , wherein said calibration signal is a noise signal that exhibits one or more of the following:

predefined spectral characteristics,

predefined signal level.

10. An apparatus according to claim 8 , wherein the adaptation means ( 152 ) is arranged to carry out the filter calibration procedure in conditions where the feedback information (f) indicates energy of ambient sound and vibration that is below a predefined threshold.

11. An apparatus according to claim 2 , wherein the driving means ( 150 ) is arranged to

derive a first cancellation signal by multiplying the first feedback signal (f 1 ) by a first adaptable gain value (g 1 );

derive a second cancellation signal by multiplying the second feedback signal (f 2 ) by a second adaptable gain value (g 2 ); and

generate the driving signal (d) as a signal that includes a combination of the first and second cancellation signals.

12. An apparatus according to claim 4 , further comprising an adaptation means ( 152 ) arranged to carry out one of the following:

derive respective values of the first and second adaptable gains (g 1 , g 2 ) such that the energy of the driving signal (d) is minimized, thereby reducing both the kinetic energy and the potential energy of ambient sound and vibration induced inside the padding ( 170 );

set the value of the first adaptable gain (g 1 ) to zero and derive the value of the second adaptable gain (g 2 ) such that the energy of the driving signal (d) is minimized, thereby reducing the potential energy of ambient sound and vibration induced inside the padding ( 170 );

set the value of the second adaptable gain (g 2 ) to zero and derive the value of the first adaptable gain (g 1 ) such that the energy of the driving signal (d) is minimized, thereby reducing the kinetic energy of ambient sound and vibration induced inside the padding ( 170 ).

13. An apparatus according to claim 5 , further comprising an adaptation means ( 152 ) arranged to carry out one of the following:

derive respective values of the first and second adaptable gains (g 1 , g 2 ) such that the energy of the driving signal (d) is minimized, thereby reducing both the kinetic energy and the potential energy of ambient sound and vibration induced inside the padding ( 170 );

set the value of the first adaptable gain (g 1 ) to zero and derive the value of the second adaptable gain (g 2 ) such that the energy of the driving signal (d) is minimized, thereby reducing the potential energy of ambient sound and vibration induced inside the padding ( 170 );

set the value of the second adaptable gain (g 2 ) to zero and derive the value of the first adaptable gain (g 1 ) such that the energy of the driving signal (d) is minimized, thereby reducing the kinetic energy of ambient sound and vibration induced inside the padding ( 170 ).

14. An apparatus according to claim 11 , further comprising an adaptation means ( 152 ) arranged to carry out one of the following:

derive respective values of the first and second adaptable gains (g 1 , g 2 ) such that the energy of the driving signal (d) is minimized, thereby reducing both the kinetic energy and the potential energy of ambient sound and vibration induced inside the padding ( 170 );

set the value of the first adaptable gain (g 1 ) to zero and derive the value of the second adaptable gain (g 2 ) such that the energy of the driving signal (d) is minimized, thereby reducing the potential energy of ambient sound and vibration induced inside the padding ( 170 );

set the value of the second adaptable gain (g 2 ) to zero and derive the value of the first adaptable gain (g 1 ) such that the energy of the driving signal (d) is minimized, thereby reducing the kinetic energy of ambient sound and vibration induced inside the padding ( 170 ).

15. An apparatus according to claim 4 , wherein the driving means ( 150 ) is arranged to

process the first feedback signal (f 1 ) by a first compensation filter (H 1 ) that is arranged to model an inverse of a first transfer function from the driving signal (d) to the first feedback signal (f 1 ); and

process the second feedback signal by a second compensation filter (H 2 ) that is arranged to model an inverse a second transfer function from the driving signal (d) to the second feedback signal (f 2 ).

16. An apparatus according to claim 5 , wherein the driving means ( 150 ) is arranged to

process the first feedback signal (f 1 ) by a first compensation filter (H 1 ) that is arranged to model an inverse of a first transfer function from the driving signal (d) to the first feedback signal (f 1 ); and

process the second feedback signal by a second compensation filter (H 2 ) that is arranged to model an inverse a second transfer function from the driving signal (d) to the second feedback signal (f 2 ).

17. An apparatus according to claim 11 , wherein the driving means ( 150 ) is arranged to

process the first feedback signal (f 1 ) by a first compensation filter (H 1 ) that is arranged to model an inverse of a first transfer function from the driving signal (d) to the first feedback signal (f 1 ); and

process the second feedback signal by a second compensation filter (H 2 ) that is arranged to model an inverse a second transfer function from the driving signal (d) to the second feedback signal (f 2 ).

18. An apparatus according to claim 9 , wherein the adaptation means ( 152 ) is arranged to carry out the filter calibration procedure in conditions where the feedback information (f) indicates energy of ambient sound and vibration that is below a predefined threshold.