Ever notice the pointless nodules jutting off the intake tube running into a car’s throttle body? They do have a job. These air cavities are called resonators, and their job is totally non-intuitive. Everything in nature has a resonant frequency, a point where an applied frequency coupled with the part’s mechanical properties results in amplification of the vibrations. Engines are basically vibration machines, so managing the sounds takes a lot of engineering. Fortunately, resonant frequency can be controlled by changing the volume of an air space. (Think moving the slide on a trombone.) Tuning that extra space means the intake makes only pretty sounds (or none at all) in the normal rev range of an engine. Science!
By Ben Wodjdyla