There is more then one reason. All THX speakers and subwoofers are sealed designs. As far as I know all movie theaters use sealed speakers and subwoofers. Acoustic suspension speakers and subwoofers can usually take more abuse at high SPL levels then a ported cabinet without blowing the speaker or bottoming out the driver. You need to be more careful and listen to a ported subwoofer the harder you play it compared to a sealed subwoofer.