Birch multiplex bass reflex subwoofer with more sound pressure. The standard bass-reflex subwoofers form the solid foundation of the new LINEAR 5 MK2 systems with their uncompromising performance and dry, defined bass down to the lowest of the lows. Cardioid settings that can be simply selected via a preset give the user an enormously expanded range of options for system configuration and access to the professional class. 2.1 setups are simplified thanks to the stereo preamplifiers.