NVX Active Noise Control Systems reduce interior, average propeller SPL and SPL gradients regardless of the synchrophasor setting. Propeller tones are comprised of multiples of the fundamental blade passing frequency. In most cases, the fundamental frequency is between 70 and 130 Hz. The fundamental, first and second harmonics are, usually, the prime contributors to cabin noise. Thus, the frequency range of interest is between 70 and 390Hz.
Passive noise absorbing treatments have only limited impact on propeller noise.
Since the complexity of disturbance paths can often make it difficult to isolate noise at its source, Active Noise Control provides local control using speakers placed inside the cabin. Microphones detect cabin noise, and the electronically controlled speakers replicate a mirror image of the sound pressure field in the cabin. Not only is the fundamental frequency of the disturbance canceled, the harmonics are also canceled. NVX Active Noise Control is certified on the Beech King Air and the Cessna Conquest . In addition to fixed wing solutions, Lord has demonstrated NVX Active Noise Control on helicopters.