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 design difference provides a smoother motion for the woofer's membrane, enabling greater excursion and better sound quality compared to traditional speaker designs that rely on rigid mechanical support.