This paper presents the results of research of active control of noise. The authors built a prototype to lower the direct field of a known source using a linear array of 40 loudspeakers controlled by delay lines and a digital signal processor. The inspiring theoretical tool is wave field synthesis (WFS), an holographic approach to sound control, which was proposed by Berkhout, et al., in 1988, at the Delft University of Technology. An average reduction of 3 dB was obtained on an area of 16-square meters for a frequency of 1000 Hz.:
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