The air intake resonator is simply an expansion chamber, a wide spot within a car's intake pipe. Resonators come in two types: in-line resonators, which are open chambers fitted in the intake tube, and side branch resonators, which are chambers that sit next to the intake tube and are connected to it via a small channel or duct.
A common misconception among many auto enthusiasts and hot-rodders is that the air intake resonator is there for the sole purpose of muffling the sound of the engine on an older car. While dampening the sound of the engine is one of the purposes of the air intake resonator, it is not the primary purpose. The primary purpose of the air intake resonator is to inhibit pressure wave harmonics, which causes air pressure in the engine and restricts the amount of airflow through the RPM spectrum. In effect, the air intake resonator, via its expansion chamber, slows down the air emerging from the engine. This reduces the engine intake noise and increases the amount of horsepower available.Learn more about Car Parts & Maintenance