Pressure Vessel Active Subwoofer - The Bowers and Wilkens PV1 reinvents the subwoofer by combining contemporary design that fits harmoniously in the home environment with a unique sound-orientated construction. The subwoofer owes its curved shape to sound engineering principles - those of a pressure vessel (PV). The spherical form is the ideal shape to accommodate pressure differences between the inside and outside of the enclosure and proves quality bass can be achieved using a small cabinet. The aluminium construction virtually eliminates cabinet resonance and produces cleaner bass than a conventional subwoofer, because the drive units devote their energy to driving air, not the cabinet. The cabinet also acts as the amplifiers heat sink and the drive units are especially designed so not to require a grille.