Measurements of the performance of an acoustical calibration duct

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