MEASUREMENTS OF THE PERFORMANCE OF AN ACOUSTICAL CALIBRATION DUCT

This note details an investigation of the performance of an acoustical duct used for the calibration of devices such as microphones, sound l evel meters and sound intensity probes at frequencies less than 250 Hz . The accuracy of the plane wave field produced in the duct was examin ed by measuring the standing wave ratio in the duct and the sound pres sure level variation across a cross-section of the duct. The results s uggest that the duct should only be used to compare pressure responses of acoustical measuring devices of similar physical dimensions.