Active Noice Reduction headset

Abstract: Conventional (passive) headsets used in propeller aircrafts are reasonably good at attenuating mid to high frequency noise, but fail to achieve good attenuation in the low frequency region (below approximately 300 Hz). Active Noise Reduction (ANR) improves the low frequency attenuation by introducing an anti-noise signal creating destructive interference thus decreasing the residual noise level. The aim of this thesis is to develop and implement a digital narrowband active noise reduction headset that works properly in aircrafts and not only in a laboratory environment. The implementation is based on a narrowband ltered-X least mean squares (FXLMS) algorithm where the tonal components in the noise spectrum are synthesized for use as reference signals to the algorithm. The controller is implemented in a parallel fashion where each tonal component is handled separately. The system is built into a headset and laboratory tests show that the algorithm can handle ve simultaneous tonal components with an adaptation time of less than one second. Aircraft tests show peak attenuation of 17 dB in both singleand twin-engine aircrafts thus fullling the requirements. Simulations and true performance show some minor discrepancies which are explained and discussed.