Originally Posted by amc49
Intake air resonation can be easily affected by a simple closed end box as it changes the resonating frequency of the intake stream. There are sonic waves there just like in an exhaust muffler and they if getting timed right greatly increase noise if the setup is messed with. You have air going into engine but some of it backs out to come back out the intake at certain rpm when the lengths and displacement of the intake tract line up wrong to do it. They often correct by adding airbox volume (empty dead-end box to make you go ????, it is a wave strength absorber) to alter the resonation frequency of the tract and it stops much noise. As well, the resonation control method can add a decent chunk of very low rpm torque as the resonation at lower speeds can mess with the injection in intake ports to create backflow that affects off idle performance.
Thank you for the beautiful explanation. I don't doubt you, but wouldn't the PCM on these newer cars correct the timing and intake to the adjusted airflow? It's hard to quantify but it seems a lot of people enjoy these variations to the stock induction system (e.g. open lid, open air filter, snorkel delete, intake resonator delete), albeit they might not understand how they're affecting the system. Or is it a matter of trade-off / personal preference...