An experimental investigation of the active control of sound transmission into a cylindrical enclosure

Preliminary results are reported from experiments involving the use of vibration sources in the active control of sound transmission into a cylindrical chamber (as in aircraft cabin-noise suppression). Electrodynamic shakers are used to provide vibrational excitation in a 3-m-high 900-mm-diameter cylindrical stainless-steel chamber with damped ends, subjected to single-frequency (384-Hz) sound from a horn driver located 150 mm from the cylinder midway along its length. When vibration is applied only diametrically opposite the source, rotation of the sound field occurs, but global attenuation is not achieved; with additional vibration applied at an angle of 225 deg to the source, moderate reduction of the global field is obtained. The need to identify and control all offending coupled structural/acoustic modes is indicated.