Measuring the acoustic properties of ducts

Abstract A short review, with examples, is given of a two-microphone transfer function method intended for making measurements in a tube or duct system. The method, originally proposed by Chung and Blaser, has proved useful in measuring the absorption coefficient, impedance and transmission loss, when dealing with plane wave propagation, i.e. for frequencies below the duct cut-off frequency. For the purpose of measuring the transmission loss of duct elements, a possible means of extending the useful frequency range by two or three octaves is proposed, based on subdividing the actual duct, at the measurement site, into a bundle of smaller, parallel ducts.