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.
Unlike traditional speaker designs that rely on a stiff physical connection, the enclosed space of a sealed-loudspeaker provides a smoother, more linear motion for the woofer's membrane, enabling greater excursion and better sound quality.