A New Active Headset For a Helicopter Application

In helicopters, the low frequency noise generated by the rotors and engines often masks and jeopardizes safe communication. Additionally, pilots are likely to suffer from hearing damages due to the higher sound levels in the headset produced whencompensatingfor the noiseby increasedspeakerlevels. A feasible approach is to reduce the low frequency noise using active techniques, thereby enabling lower speakerlevels. In many Active Noise Control (ANC) applicationsthe primary noise field is either periodic or broadband which simplifiesthe choice of algorithm. In our application, noise up to 100 Hz is dominated by tones and in the range from 100 Hz to 400 Hz the noise characteristicsis more broadband. In order to achievean efficientattenuationof the primarynoise, a combination of a digital feedforward controller and an analog feedback controller is employed. The feedforwardcontroller is tachometerbased and reducesthe tonal components, whilethe feedback controller attenuatesthe more broadband noise. In this paper, a combination of these two techniquesis evaluatedon real data.