Abstract: In this paper, the energy formulas of Active Sound Absorption (ASA) in space sound field has been derived from the basic sound wave equation, and the ASA including the relevant conditions of multipole secondary-source, such as monopole, dipole and tripole, etc., has been discussed. On the basis of the discussion, it has pointed that dipole secondary source-configuration (DAA) is the simplest attenuator. The results of experiments done in anechoic chamber have shown that DAA has effective performances which just provide the fundation and feasibility of practical use.