L SUB 4000 A is a flexible 18″ double vented bandpass subwoofer. Compatible with all LINEAR 5 fullrange speakers and mid/high units, its powerful low end – ranging from 30 to 100 Hertz – is totally and powerfully impressive. L SUB 4000 A can also serve as a sub-low add-on to LINEAR SUB 2000 to beef up the bottom end in the range of 30 to 70 Hertz.