RP-478 -- Determining the the Physical Properties of Fibrous Duct Lining Materials and Their Sound Attenuation Properties PDF

This research was funded by the American Society of Heating, Refrigerating and Air Conditioning Engineers, Inc. under Research Project RP-478. 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, 3 meter (m) (10') long, ducts of three cross sections 0.305 x 0.61 m, 0.61 x 0.61 m, and 0.915 x 1.22 m (l1 x 2', 21 x 2', 31 x 41) were tested. Four material types (specified as: 1" @ 1.5 lb/cu ft, 1" @ 3 lb/cu ft, 2" @ 1.5 lb/cu ft, 2" @ 3 lb/cu ft) were used. The physical and acoustical properties of each material were measured. These properties were: 1) t h e normal specific acoustic impedance and absorption, 2) the wave propagation parameters, 3) the fiber sizes, 4) the density, and 5) the flow resistance of the liner and its components. This research has lead to the development of a method for predicting acoustic attenuation in a lined HVAC duct. The method is a modification of the present two-part method [ASHRAE Systems Handbook 1984] to a three - part method which approximates both plane-wave and cross-mode attenuation.