What is the use of filtering the black box on the roof?

The little black box you mentioned, to be exact, is called the air intake resonance box. One is to reduce the intake noise, and the other is to help the throttle to achieve the optimal intake flow in the shortest time when inhaling, because the air filter box is generally at a certain distance from the throttle to get an optimal control ratio of the intake flow of the vehicle (generally this length is calculated according to the form and displacement of the engine). However, this will lengthen the intake flow process after the throttle is opened, so later models set a small resonance box on the intake pipe behind the air cleaner to help store air, so as to shorten the intake speed when the throttle is opened and reduce the intake noise. I hope I can help you.