Acoustic field conformation using multichannel active noise control techniques

This paper describes the experimental application of sensors array and multichannel digital signal processing to the equalization of the acoustic field in car compartments. The aim of this multichannel active noise control system is not simply to cancel undesirable noise but to reshape the sound field around the listener´s head. A modified version of filtered-X LMS active noise equalizer algorithm has been developed and extended to multiple channels. A 4100 type Bruel dummy head and torso with two calibrated microphones at the ear´s canals has been used to obtain sound levels in an hypothetic listener´s ears. The equalization points are not only the error sensors position but an area around them which is measured using the manikin. It has been found that at low frequencies the zones of equalization created around the point of control are large enough to cover the movements of the head without disturbing algorithm´s stability