Input impedance measurements of conical acoustic systems using the two-microphone technique

Abstract

The two-microphone technique with a broadband excitation has been used for the measurement of various objects including straight conical waveguides and alto saxophones. An improved procedure has been developed whereby the noise excitation signal is pre-filtered by the inverse frequency response of the system under consideration. This approach helps reduce distortion and improves the SNR of the measurement. Results with and without pre-filtering are compared for different fingerings of an alto saxophone. The input impedance of a straight conical waveguide is compared with theory and discrepancies are analyzed. The input impedance of saxophones are evaluated with the transmission matrix approach and compared with measurements. A software environment for efficient comparison and analysis of measurement data with theoretical calculations is presented. We also propose a framework for sharing raw measurement data among researchers to allow comparison of results obtained with different apparatus on similar objects to better quantify their accuracy.