This is true subwoofer circuit. This circuit is used for 15- to 18-inch woofers and will not work with 8- or 6- inch “subwoofers.” It has bass-reflex, a good infinite-baffle, or foldedhorn enclosure, and driven by driven by an amplifier with at least 100 watts. This circuit will most useful for home theater applications, which play material that does have subsonic audio content, such as the dinosaur stomp in “Jurassic Park” and “Earthquake.” Here is the circuit :
Gain of this filter is 20 dB to 13 Hz, rolling off to unity gain at about 40 Hz. It is below human hearing range, and it is not designed to be heard but to be felt. In the United States, there is no the broadcast material that extends below 50 Hz and even most audio CDs do not go below 20 Hz. You can use a passive (resistors) voltage divider for VCC/2 or you can use an active virtual ground circuit. [Source: Analog Application Journal]
