This is a powerful single 18” subwoofer in a vented enclosure. The cabinet is well braced and has two 6” diameter ports for excellent high-level output. The 18” woofer has a 4.5” voice coil. It comes with a top hat for a pole-mounted satellite speaker. The TL 18.1 is also available in permanent install version with no handles, top hat, and has a barrier strip connector.