FBT SUBline 12Sa 600W Active Subwoofer, 129/133dB SPL Processed Active Subwoofer. The SUBLINE 12Sa subwoofer is built in birch plywood and aimed to extend the low frequency response to a wide range of FBT speaker systems. The FBT Subline 12-SA was created with the aim to maximize SPL/SIZE ratio and features a Class D amplifier, switch mode power supply and Digital Signal Processor with presets to match any other FBT speaker. With IN/OUT stereo connectors, it is possible to use only one subwoofer with Left and Right speakers. Optional wheels, ergonomic integrated carrying handles and plywood cabinets allow an easy transport.