Improved Direct–Parallel Active Noise Control Systems for Narrowband Noise

Narrowband active noise control (NANC) systems are extensively used to cancel narrowband noise. Direct, parallel, and direct–parallel NANC systems use nonacoustic sensors to measure rotational speeds, and a bank of signal generators then produces synchronized sinusoidal waveforms as reference signals corresponding to the fundamental frequency of the undesired noise. The performance of direct NANC systems is based on the frequency difference between two adjacent reference input sinusoids. Parallel NANC systems apply several sinewave generators and two-weight adaptive filters in parallel to attenuate these narrowband components. Conventional direct–parallel NANC systems split these sinusoids into several mutually exclusive sets such that the distance between frequencies within sets is maximized. This paper proposes an improved direct–parallel NANC system in which reference sinusoidal signals are separated by amplitude to enhance efficiency and improve noise reduction performance. Several experiments were conducted using a muffler model to verify the performance of the proposed NANC system.