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We present in this paper an active anechoidal termination composed of a porous materiai, whose absorbent properiies are improved by a secondary source. A simple model of amustic propagation in a porous medium leads to optimal absorption criteria, which are verified by absorption coefficient measurements under normal incidence at the end of a Kundt duct. A secondary source is placed at the backward interface of the material, and imposes zero pressure by destructive interferences, which is a necessary condition for the maximum absorption. Several control set-ups are tested and provide the anechoism for broadband excitations.

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