Measurement of acoustic power output in the active control of sound

Active sound control can be used to obtain large global reductions in low‐frequency harmonic enclosed sound fields. The secondary sources of sound in such applications have typically been adjusted to minimize practical approximations to the total acoustic potential energy in the enclosure. Minimizing the total acoustic power output of the primary and secondary sources has recently been theoretically shown to give very similar results. In this paper, some of the physical consequences of minimizing total power output are discussed, specifically the implications this has on the power output of the secondary sources. In the single channel case, it is found that the acoustic power output of the secondary source is exactly zero when adjusted to minimize the total power output of both sources. A method of adjusting the secondary source to achieve this objective is presented, in which the volume velocity of the secondary source is adjusted to be out of phase with that of the primary source, and the secondary sour...