Beyma 18" SM-118 800 Watt 8 Ohm SQ IB OB Woofer Subwoofer 3" Voice Coil

High quality subwoofer with good efficiency and long linear excursion.  These are great for infinite baffle or open baffle designs such as H-frame thanks to a relatively high Qts.  High end low power DIY audiophiles will love this in large vented boxes also.  See the datasheets in the images.