Air box

There's a number of opinions on why the air box is installed in the intake upstream the throttle body. Some say it's for immediate delivery of air when the throttle is rapidly opened, some think it's destined for elimination of induction noise the air makes passing through intake duct. It doesn't seem credible, or to put it differently - it seems like there's something else or different it's needed for. Could you please shed some light on this issue?

On many cars, the airbox is just the way to seal the air filter to the throttle. It's size and shape can have some small effect on performance, but providing cool, clean air to the engine intake is the primary function.

Understood. Thank you

As David said, mostly convenient for enclosing the air filter and routing air from outside the vehicle to the engine.

Some are indeed shaped to reduce intake noise at certain RPM when a resonance may cause an annoying drone, some may also be tuned to introduce a resonance for more torque in other rpm ranges. Oh, and some are useful for positioning the vivertion valve to balance intake air temperature by drawing air from around the exhaust in cold weather.