Yamaha’s BASS (Bass Action Selector Switch) tailors the sub’s output for video or music at the touch of a switch. Two sets of inputs let the sub accept either line- or speaker-level inputs, while a handy phase normal/reverse switch makes it easy to phase the subwoofer with the other speakers in your system.
https://www.amazon.com/Yamaha-Corporation-America-SW315-Subwoofer/dp/B00009W8XH

