Error Microphone Placement Optimization for Concurrent MIMO Feedback ANC Systems

The use of active noise control (ANC) systems in automotive applications has been common practice for well over a decade. Many of these systems utilize at least one error microphone that is placed inside the vehicle cabin and provides feedback to the algorithm in order to assess the effectiveness of the anti-noise signal as it attempts to cancel primary noise. Prior work pertaining to optimal error microphone placement has not provided any objective metrics that correlate to the noise reduction experienced inside the vehicle cabin. The goal of this paper is to establish empirically-based metrics which can be used to quantitatively describe why one microphone position in the vehicle is superior or less favorable when compared to another. These metrics are used when considering concurrent multiple-input multiple-output (MIMO) ANC systems that utilize the same error microphones but are trying to attenuate both broadband and narrowband noise. Empirical correlation of these metrics with respect to the noise reduction achieved is shown with in-vehicle acoustic measurements. Cross-correlation effects were observed between error microphones in different quadrants of the vehicle; however, an average of the metrics and the noise reduction across all quadrants of the vehicle showed a meaningful correlation that can be used as the basis for further development of this methodology.