HK Audio LINEAR SUB 1800 A Active Bass Reflex Subwoofer, 1200W Power - 18"L SUB 1800 A A LOW END BOOST FOR THE LINEAR SERIESLINEAR SUB 1800 A an 18" bass reflex subwoofer is packed full of low end. Unrivaled power, SPL of up to 132 dB and thumping bass (all the way to 38 Hz) make this powered sub the ideal add on to mid high units from the LINEAR 3 family when you need just a little more loudness and low end. LINEAR SUB 1800 A can also be used in combination with mid high units from the LINEAR 5 family, or as a bass