A damper for circular ducts. It is made of soft elastic plastic foam with good damping abilities.
The damper has a number of oval openings equipped with releasable plugs and the pressure drop across the damper is adjusted by varying the number of open holes.
Due to the material and the design of the holes, sound generation will be low even at large pressure drops. The plastic foam has an open cellural structure and high density, which makes an ability to absorb sound and the damper acts as a simple silencer.