The SHFS12B is a powered subwoofer containing a high power 400 Watt amplifier in combination with a 12" injection moulded long-throw woofer. The crossover frequency is adjustable between 50-150Hz. The subwoofer takes care of the frequencies below the set value and thus relieves the other speakers in the system. The phase is to adapt where you can choose from 0 or 180 degrees. The stereo RCA input