RCF SUB 708-AS II Powered Speaker. The SUB 708-A S II is the ideal device to boost the low end performance of a portable PA system, both in terms of output and frequency extension, thanks to the potent 18" woofer with 3.0" voice coil and the 1400-Watt amplifier. It is simple and quick to set up as a satellite speaker system because of the built-in digital stereo crossover (DSP) with customizable crossover frequency. The SUB 708-AS II pairs flawlessly with satellite speakers that are 12" or 15". The RCF ART 3, ART 7, or D-Line Series subwoofers pair best with the SUB 708-AS II.