Abstract: This paper traces the development of noise criteria as applied to buildings——thelow elvels of sound that people want to have when they sleep, work, and relax. It then leads into the typical sources of sound in ducted ventilation systems and gives an historical review of the major acoustical problems in mechanical equipment systems over the past 20-25 years. The paper concludes with a. series of pictures illustrating state-of-the-art applications of vibration isolation techniques for mechanical equipment.