The ST-218 is a large format touring subwoofer, and whilst it is designed to be mechanically and acoustically compatible with the HALO-A system, it is a standalone product in its own right and can be used to support any EM Acoustics product – either in a flown or ground stack configuration.

The compact enclosure houses a pair of 4.5” voice coil, 18” (457mm) neodymium drive units, in a reflex design with a single low-velocity port to minimise distortion. The drive units’ high motor strength gives the ST-218 excellent transient response, and the moving area of the two high-excursion 18” drive units generate significant low frequency extension and overall output. The enclosure is symmetrical, so in both flown and ground stacked configurations one enclosure in every three can be rotated to create a cardioid array. Such arrays offer exceptional low frequency directivity control and significantly reduce the energy radiating to the rear.

The robust enclosure is constructed from premium 18mm (¾”) multi-laminate Birch plywood – rebated, screwed and glued together for maximum strength. The enclosure is finished in a rugged black textured polyurethane finish or white textured paint as standard, however RAL colour matching and weather-protected outdoor installation options are also available. Input is provided by a single NLT4MP connector on the rear.

The flying hardware has been built with touring flexibility and reliability in mind. The ST-218 uses a 4-point system, and all rigging components retract flush for transit and ground stack use. Ultra-high tensile steel parts form the core of the 4-point system, meaning arrays of up to 12 elements can be safely assembled with above-regulation safety factors. The mechanical package is completed by a mesh-backed steel grille, eight recessed bar handles (four per side), protective stacking runners and mating recesses and attachment points for the optional castors on the rear.

The ST-218 requires external active high/low pass filters and a single amplifier channel to function correctly – as such it is recommended to be used with the DQ20 advanced system amplifier.

Optional accessories include castor sets, multi-enclosure touring wheel-carts, flying grids and padded covers for both single enclosures and multi-enclosure carts.