Anechoic Broadband Compact (ABC) Muffler with Moving Blade and Vehicle Applications

A muffler has a first plate with multiple holes; a second plate with multiple holes; the first plate mounted at a distance across an entire area having holes of first and second plate that is less than or equal to two millimeters above the second plate; and an additional feature selected from a back cavity and an acoustic membrane over holes of the first plate. In embodiments, none of the holes of the first plate are directly aligned with holes of the second plate. In embodiments, the first plate is mounted at a distance above the second plate that is no more than twice the Stokes boundary layer thickness estimated at a first predetermined frequency. The muffler may be disposed on a surface of a blade of a fan or wind turbine. The muffler may also be used to quiet a centrifugal blower or a vehicle.