An acoustic structure and a method for dampening sound. The acoustic structure includes an acoustic absorber having one or more acoustic elements. The acoustic absorber is disposed inside a volume. The acoustic structure further includes an acoustic radiator having one or more acoustic elements. The acoustic radiator is disposed outside the volume. A cross-sectional area of the one or more acoustic elements decreases with a distance from a mouth of the one or more acoustic elements to a throat of the one or more acoustic elements. The acoustic structure also includes one or more acoustic waveguide ducts configured to acoustically couple the acoustic absorber and the acoustic radiator.