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

This paper is mainly intended to discuss the physical understanding of active control on the primary source in a pipe. The derivation of some acoustic fields involved, the measurement of the sound source impedance in either an active or non-active control situation by using a Helmholtz resonator, and the comparison between two results as obtained are included in this study. In order to demonstrate the feasibility of the measurement of source impedance 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 method. The results as obtained by using the above two methods agree reasonably well.