Basically, a passive radiator is a reactionary device as the name suggests. When a driver (such as a subwoofer) is mounted to a sealed speaker box (enclosure), the physical forward/back movement of the speaker affects the internal air pressure of the enclosure.
Three landforms created by wind are; sand dunes, yardangs (half-teardrop shaped formations hill sized, and deflation hollows (wind swept depressions.
1 A stump is the landform formed when a stack is eroded leaving a small piece of rock visible at high tides. 2  Attrition is a process of erosion caused when rocks and boulders, transported by rivers and waves, bump into each other and break up into smaller pieces.