JBL S2-1224SS Sub 12 Inch Slipstream Ported Subwoofer Enclosure 275w RMSJBL S2 1224SS 12" (300mm) Slipstream ported enclosure Our patented port brings the bass, not the noise. Series II enclosure deliver the enhanced efficiency and higher output of a vented enclosure, without the distracting noise or chuffing generated by a port. The patented Slipstream port dramatically reduces port noise at high sound pressure levels by minimizing airflow turbulence. With high roll surrounds, proprietary cone design and long excursion,