The first one uses the discovery that sound pressure could be attenuated when it passes through a plasma sheet. The second one, and being more widely used, is to actively suppress the flow-field that is responsible to flow-induced noise (also known as aeroacoustics), using plasma actuators. It has been demonstrated that both tonal noise[7] and broadband noise[2] (difference can refer to tonal versus broadband) can be actively attenuated by a carefully designed plasma actuator.