Audio Engineering Society UK

Title: ‘Active Acoustic Absorbers: A Feasibility Study’
Location: Royal Academy of Engineering, London
Description: Lecture by John Vanderkooy, University of Waterloo and B&W Loudspeakers Ltd
Start Time: 18:30 for 19:00
Date: Tuesday 27th April 2010

An active acoustic absorber must sense the sound field in a space, and generate a signal to absorb energy from that field. In 1-D such absorbers work very well in situations such as ducts, and in 3-D systems they are effective if source and canceller are much closer than a wavelength. In actual rooms with loudspeakers, such conditions never apply. A tutorial is presented outlining the known theory and possibilities of active absorbers that work over a wide band. The self-pressure of the absorber complicates its operation, and an analysis is presented in which this self-pressure is cancelled by a signal related to cone motion. The resulting device may still suffer from implementation problems. Experiments are discussed that determine the required microphone signal that needs to be applied to the adjacent absorber driver. Active absorbers can also act as subwoofers. To conclude the talk, some FDTD calculations are presented which show how a subwoofer excites room resonances, and the influence of different configurations. Delay-and-cancel techniques lead to a very flat bass response, but that probably removes too much of the room acoustics.