Adaptive noise reduction in aircraft communication systems

It has been reported that the application of broadband noise cancelling techniques to the control of aircraft cockpit noise pickup is only successful at low frequencies. This effect is explained in terms of measures of the noise transmission across a standard British oxygen mask and a discussion of the spatial characteristics of the cockpit´s acoustic field. A theoretical prediction of the maximum noise reduction given by a single channel noise cancelling system controlling a group of independantly excited noise transmission paths is presented.