Figure 1. Side branch resonators in a duct. A & B incident, and reflected wave amplitudes, S & L cavity cross sectional area and height, S1 & S2 cross sectional area of upstream and downstream duct, and D & Ln are the neck diameter and length

From

Low Noise Intake System Development for Turbocharged I.C. Engines Using Compact High Frequency Side Branch Resonators

Sabry Allam

Advances in Powertrains and Automotives. 2015, 1(1), 12-23