A plenum with features to disperse acoustic energy in an airflow while maintaining a relatively small pressure drop in the airflow is disclosed. A general structure of the plenum may include a perforated airflow passage surrounded by a substantially large space enclosed between the airflow passage and a plenum. The perforated airflow passage has a perforated wall that may allow the acoustic energy to be dispersed into the substantially large space when flowing through the airflow passage. Acoustic energy dispersing materials may also be disposed in the substantially large space and/or on the perforated wall to help disperse acoustic energy by, for example, absorbing the acoustic energy. The plenum can help disperse the acoustic energy while helping minimize the pressure drop in the airflow.