Patent ID: 6959092

Claim:
Noise reduction arrangement comprising: a plurality of actuators ( 3 ( n )) for generating secondary noise (p s ) to reduce primary noise (p p ) generated by at least one primary source ( 4 ); a plurality of sensors ( 2 ( m )) for sensing a total amount of noise resulting from the primary noise after being reduced by the secondary noise and for generating a plurality of sensor signals (p(m)); control means ( 5 a (i), 5 b (i)) for controlling the actuators ( 3 ( n )) based on the sensor signals (p(m)), a distance (d) between the plurality of actuators ( 3 ( n )) and the plurality of sensors ( 2 ( m )) being selected to have an optimised reduction in power RP of the total amount of noise relative to the primary noise within a predetermined frequency band, characterised in that the plurality of actuators ( 3 ( n )) are located in a first two dimensional array in a first surface; the plurality of sensors ( 2 ( m )) are located in a second two dimensional array in a second surface arranged substantially parallel to the first surface; the plurality of actuators ( 3 ( n )) are sub-divided into a plurality of sub-sets of actuators ( 3 ( n )); the control means ( 5 a (i), 5 b (i)) comprise a plurality of controllers ( 5 a (i), 5 b (i)), each controller ( 5 a (i), 5 b (i)) being arranged to receive sensor signals of a sub-set of said plurality of sensors ( 2 ( m )) and arranged to control one single sub-set of actuators ( 3 ( n )); and said first and second surfaces are arranged at such a mutual distance that the reduction of power RP is within the following range: 0.9 ×RP max ≦RP≦RP max in which RP max is maximum obtainable reduction in power of the total amount of noise relative to the primary noise at an optimum distance between said first and second surfaces as established by testing, where both RP and RP max are expressed in decibel, the plurality of actuators being arranged in rows and columns, mutual distances between adjacent columns and mutual distances between adjacent rows being equal to a predetermined actuator distance d x , the plurality of sensors being arranged in the same way as the plurality of actuators, the distance d between the first and the second surfaces meeting the following condition: 0.5 ×d x ≦d≦d x .