Digital Signal Processing and System Theory

Talk Jullie Lindsay Torres

Active Noise Control

Date: 01.12.2011, 13:00 h - 14:00 h, Room: Aquarium

Jullie Lindsay Torres
CAU, Kiel, Germany


In almost all environments the control of acoustic noise has been one of the biggest challenges over the years. Nevertheless, for a long period of time the proposed solutions only included physical barriers and not active adaptive components. This caused solutions to be not practical in space, expensive and not effective for the noise reduction in all frequency ranges.

Fortunately, since 1936 when Lueg proposed his patent in order to use a microphone and a loudspeaker to create an active cancellation noise signal, the Active Noise Control (ANC) system has evolved. The study of the possible active solutions now includes more complex definitions, all of them based in the simple acoustic principle of superposition. This principle consists in the addition of two signals in the acoustic domain, which due to their opposite characteristics cancel each other. The effect that the superposition principle produces is present only if the ANC system is situated near to the listener, i.e., in the area comprised between the ANC's loudspeaker and the listener's ear. The amount of noise signal canceled by the anti-noise signal produced in the ANC system strongly depends on the estimation's accuracy in amplitude and phase of this signal, however, it is independent of the noise source position.

Nowadays, ANC systems have applications in noise control inside cars, in ducts, aircrafts, boats and in industrial noise control, among others. This progress brings implicitly competition between the companies in order to provide the market more complex and efficient noise reduction solutions for specific kinds of noise and scenarios.

The aim of this thesis is to implement a feedforward ANC system for closed headphones, which cancels different noise disturbing signals that come from any outside point and can affect the playback of the desired local signal, like speech or music. In the implementation, the acoustic environment as well the signal processing domain in which the headphones are involved, are included. Furthermore, different approaches to improve the ANC system effectiveness are described and integrated in the solution.