AT-2477-2478 (RP-196) -- A Review of the Attenuation of Sound in Straight Lined and Unlined Ductwork of Rectangular Cross Section PDF

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 economicaI 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, the ASHRAE Technical Committee TC 2.6 has realized the need to improve the accuracy of information to permit optimal noise control design of HVAC systems. Committee members therefore initiated a two-phase research project, designated TRP-196. The first phase of this project, reported in this paper, is a critical review of the state of current knowledge in predicting the attePuation of sound in straight lined and unlined ductwork of rectangular cross section with airflow up to 4000 fpm. In addition, acoustical design information has been generated that allows the HVAC engineer to predict the sound attenuation in straight rectangular ducts more accurately than'with current methods.