The HD series is versatile and modular. Available as singles or double-stacked, they incorporate a high-quality Italian woofer and proprietary magnetic planar driver within a petite, sturdy weatherized cabinet, ready for installation outdoors in the landscape or on a wall. The sum of these parts results in the following: A loudspeaker the size of an average bookshelf speaker that competes with audiophile towers, and can effortlessly produce enough sound to drown-out an helicopter taking off. If you like that sort of performance.