 Unlike the stiff physical suspension built into the driver of conventional speakers, the trapped air inside the sealed-loudspeaker enclosure provides a more linear restoring force for the woofer's diaphragm, enabling it to oscillate a greater distance (excursion) in a linear fashion.This is a requirement for clean and loud reproduction of deep bass by drivers with relatively small cones.Even though acoustic suspension cabinets are often called "sealed box" designs, they are not entirely airtight.