Improvements in Active Noise Control of Helicopter Noise in Mock Cabin

Salt Lake Community College

The application of active noise control (ANC) to interior cabin noise of helicopters is a challenging problem because of multiple tones and significant broadband frequency content. The most common control approach is to use the standard filtered-x algorithm. For this algorithm, the convergence and tracking speed is dependent on the eigenvalues of the filtered-x autocorrelation matrix, with these eigenvalues being frequency dependent. To maintain stability, the system must be implemented based on the slowest converging frequency that will be encountered, which can lead to significant degradation in the overall performance of the control system. This paper will discuss an approach that has been developed which largely overcomes this frequency dependent performance, in a manner that maintains a relatively simple control implementation but significantly improves the overall performance of the control system. The favorable convergence characteristics are demonstrated through the application of helicopter noise in a mock helicopter cabin.