An acoustic resonator (20) has a resonator cavity (22) with a resonator port (24) for communicating with an exhaust flow passage (26) conducting acoustic waves therethrough. Adjustable port structure varies acoustic impedance of the port by various combinations including translation to vary area along an arcuate surface, translation between discrete areas, translation to cumulatively open port area, multiple translation, multiple ports, rotational area change, and rotational length change. Adaptive control may be provided. A combined passive and active acoustic system may also be provided.