Virtual sensors in active noise control

Abstract

Traditional active noise control systems achieve the greatest noise reduction at the locations of the error sensor(s). In many cases it is desirable to be able to achieve the maximum noise reduction remote from an error sensor. One way of doing this is to measure the transfer function between the desired location of maximum reduction and the error sensor and incorporate it in the control algorithm. The disadvantage of this method is that it is not robust to changes in the acoustic environment. Another method relies on using two or more microphones to estimate the sound level at a remote location using forward prediction. This method results in a lower performance but it can be adapted to changes in the acoustic environment as well as to changes in the location of the desired pressure minimum. This paper will report on a study that compares the relative merits of various forward prediction method in various situations. These commence with a free field environment (to introduce the concept) and then progress to a more practical application of an aircraft cabin. Single and multiple control sources will be considered as will sound pressure sensing and energy density sensing.