Rethinking Systems Analysis & Design

Method and device for reducing noise produced by propellers. Anti-sound generators (devices reproducing sound vibrations but of inverted phase) are placed in the region of the noise generation but at a spacing therefrom determined by a mathematical relationship such that the zone of noise cancellation will be at the desired zone with respect to the point of noise generation. When the noise suppression is to be through a substantial region, and variable pitch propellers, or other similar variations in the mechanics of noise generation will cause the above-mentioned spacing to vary, multiple units at varying distances from the noise source may be utilized.