Sound attenuation of dual-wall, fiberglass-lined, circular ducts with and without airflow

Abstract

A major test program for measuring the sound attenuation characteristics of dual-wall, fiberglass-lined, circular ducts from six different duct manufacturers was completed. Octave band dynamic insertion loss values for octave band center frequencies from 63 to 8000 Hz were measured. The inside diameter of the ducts that were tested ranged from 12 to 48 in. Sound tests were conducted with and without airflow. Six airflow velocities from 1000 to 6000 fpm were examined. Regression analyses were conducted on the measured insertion loss values. Regression equations for the dynamic insertion loss values were developed that can be used to estimate the dynamic insertion loss of dual-wall, fiberglass-lined, circular ducts for zero flow and for duct airflow velocity from 1000 to 6000 fpm. The equations are valid for duct diameters from 12 to 72 in.