Active Absorbers

Martial Rousseau , John Vanderkooy

This paper explores the use of bass loudspeakers as both acoustic sources and broadband absorbers. We develop the theory for a point active absorber immersed in the anechoic field from a point source. This will apply to normal loudspeakers used as either sources or absorbers at frequencies below about 300 Hz, where they act much like points. The result extends the theory of Nelson and Elliott for a point absorber interacting with a plane wave. An extra oscillatory interference term occurs which should largely cancel in rooms due to the varying distances between all the source images and the absorber. Responses were measured in several small rooms from source and absorber loudspeakers to both a few listening microphones and microphones mounted very near the absorber diaphragms. Boundary element calculations are needed to allow optimal absorber signals to be derived from the absorber microphones. We use precomputed absorber signals to avoid the serious stability issues of self-actuated active absorbers. Experimental results are not very clear and we analyze several aspects which might resolve theory and experiment.

Mots clés: loudspeaker; absorber; active

Domaines: Acoustique [physics.class-ph]

Martial Rousseau, John Vanderkooy. Active Absorbers. Acoustics 2012, Apr 2012, Nantes, France. ⟨hal-00811220⟩