When noise mitigation of rooftop units does not work as expected

A duct silencer was installed in the return air ductwork of a rooftop unit as part of noise mitigation in an existing building. After installation, the resulting noise levels had only been reduced by approximately half of what was calculated. This presentation will discuss the strategies the team took to investigate why the results did not match the calculations and how the team ultimately discovered the outdoor air damper settings of the rooftop unit were the cause of the noise problem.