Active control of sound radiation from cylinders with piezoelectric actuators and structural acoustic sensing

In this paper, analytical and experimental results of an investigation of a ctive control of sound radiated from cylinders are presented. The aluminium cylinder is 1 m in length, 25 cm in diameter and 24mm in thickness with tw o rigid end-caps at both ends. The excitation is a band-limited random nois e encompassing the first five modes of the cylinder and the control actuato rs are surface mounted piezoelectric transducers. Since it is desired to in tegrate the error sensors into the structure, the recently developed Discre te Structural Acoustic Sensing (DSAS) approach is extended to the cylindric al co-ordinates and implemented using 12 accelerometers mounted on the cyli nder. The structural acoustic sensor provides times domain estimates of far -field radiated sound at predetermined radiation angles. The controller is a 3 by 3 Filtered-x LMS paradigm implemented on a TMS320C30 DSP. The result s show good global control of the radiated sound over the frequency bandwid th of excitation. Most important, the proposed discrete structural acoustic sensor yields similar performances as error microphones located in the far field. The sensor is also shown to improve far-field attenuation over mini mization of normal acceleration at discrete locations on the cylinder struc ture. (C) 1999 Academic Press.