Boxed subwoofer flat subwoofer double subwoofer systems active closed housing series kenwood ksc sw diameter 160 mm diameter inches 6 3 inch max performance 150 watt nominal load 75 watt shape box noise level 110 db min frequency 35 hz max frequency 150 hz impedance 4 ohm weight 28 kg width 19 cm height 7 cm depth 28 cm