Active volume sound absorber

Abstract

The absorbtion cross section (ACS) of a passive volume sound absorber asymptotically equals its geometric cross section. On the other hand, the ACS of an active absorber principally could be arbitrarily large. However, the increase of the ACS results in a rapid growth of the near acoustic fields. This puts restrictions on the practically achievable values of the ACS. The talk presents the results of a simulation of sound field levels generated by active absorbers of spherical shape and different wave sizes in response to incident plane waves. It is shown that near the absorber the level of the sound field increases as compared to the passive absorber of the same size. In the far zone the field of the active absorber corresponds to the field of the passive absorber with larger geometric scale. It is demonstrated that sound energy is absorbed rather on the back side of the absorber then on its front face (with respect to the direction of incident wave).