Ductborne noise is the unwanted by-product of ventilating and air conditioning system operation. The incorporation of interior lining into duct systems is frequently the most economical control of ductborne noise because, while attenuating noise, the lining serves as a thermal insulator and introduces only a slight increase in pressure drop. Both of these nonacoustic properties of duct linings are vital in modern system design, which strives to conserve energy by minimizing operating cost.

As the volume of new building construction grows — and with it the need for some kind of interior duct lining to attenuate to acceptable levels ductborne fan noise in HVAC systems - improving the accuracy of information to permit optimal noise control design of HVAC systems became necessary. A twophase research project was initiated The first phase of this project, reported in this paper, is a critical review of the state of current knowledge in predicting the attenuation of sound in straight lined and unlined ductwork of rectangular cross section with airflow up to 4000 fpm.