The Adamson T-21 Sub is a line-arrayable bass cabinet designed to provide superior sub-bass extension for Y-Axis true line source systems. The T-21 subwoofer incorporates the newly-developed Adamson Symmetrical Drive multilayer 21" Kevlar driver. The SD-21 system employs a balanced spider suspension with spiders at both ends of the coil assembly, resulting in extreme stability under high excursions. This double spider design utilizes a 6" dual voice coil and powerful neodymium magnet to achieve superlative sensitivity. The T-21 Sub's tuned enclosure is internally braced to minimize harmonics and distortion, and features innovative port geometry that increases efficiency, lowers turbulence and has reduced compression at high SPL. The T-21 enclosure may be flown or stacked, and can be easily configured into an arc that will not shadow the main line array. The cabinet design includes an AIR rigging system with captured flying hardware that enables five precision rigging angles.