3082 (RP-478) -- The Interrelationships Between the Physical Properties of Fibrous Duct Lining Materials and Lined Duct Sound Attenuation PDF

Empirical methods were used to investigate acoustic propagation in rectangular, glass-fiber-lined, sheet metal HVAC ducts. The sample of materials was drawn from the four main manufacturers of duct liners. Fifteen, 10 ft (3.05 m) long, ducts in three cross sections were tested.

Four material types were used: 1 in. @ 1.5 lb/ft³, 1 in. @ 3 lb/ft³, 2 in @ 1.5 lb/ft³, and 2 in @ 3 lb/ft³. The physical and acoustical properties of each material, were measured. These were (1) the normal specific acoustic impedance and absorption, (2) the propagation parameters, (3) the fiber sizes, (4) the density, and (5) the flow resistance of the liner and its components. This research has led to the development of a method for predicting acoustic attenuation in lined HVAC ducts. The method is a modification of the present method (ASHRAE 1984) to a method that approximates both plane, wave and cross-mode attenuation.

Units: I-P