The Bowers & Wilkins ISW-4 is an in-wall subwoofer that is capable of pumping out vast amounts of bass while being practically invisible. Its two long-throw 200mm drivers can move the large amounts of air needed for good quality low-frequency audio. All this while still remaining subtle & hidden away. The separately purchased SA250 Mk 2 amplifier is suitable for powering this subwoofer with its 250W of power.