A physical insight of the active control on sound source in a pipe

This paper is mainly intended to discuss the physical understanding of acti ve control on the primary source in a pipe. The derivation of some acoustic fields involved, the measurement of the sound source impedance in either a n active or non-active control situation by using a Helmholtz resonator, an d the comparison between two results as obtained are included in this study . In order to demonstrate the feasibility of the measurement of source impe dance using the Helmholtz resonator technique, this study also compares the acoustic power as obtained for a sound source in a semi-infinite pipe with that measured at the anechoic termination by means of a sound intensity me thod. The results as obtained by using the above two methods agree reasonab ly well. (C) 2000 Elsevier Science Ltd. All rights reserved.