chamber

I am going through an owner's manual that I downloaded online and it mentions a "chamber air cleaner" in addition to the main air cleaner. It also says "if equipped." Do any of you guys know what the heck this is?

Changing my oil today, after removing the engine cover, I began to wonder what the chamber or box attached underneaths purpose is. It has an entry hole but there is no tube or vent that goes into this baffle. Any clue to its purpose? See pictures.