Duct fittings - such as bends, takeoffs, sudden cross sectional area changes, dampers, etc. - are important sources of HVAC system noise. They also provide a modest attenuation of the ductborne noise incident upon them.

The accurate prediction and control of flow-generated noise of duct fittings is important to HVAC engineers because at long distances from noise sources such as fans, noise from duct fittings can be the primary noise source noise.

The purpose of the Phase I investigations reported here, was to critically review the available references and data base before embarking on an extensive experimental program.