An experimental investigation of active control of vibratory power transmission in a semi-infinite cylinder, using an array of electrodynamic shakers, is described. The cylinder was mounted vertically in a sand-filled box (1 m in height) in an attempt to provide a semianechoic termination at one end. The other end was simply supported using a steel ring. The cylinder was excited near the simply supported end using a primary shaker. Control was implemented using three control shakers applied downstream from the primary shaker. Using three control shakers it is possible to achieve a 7-dB reduction in power transmission. Although 7 dB was the maximum power reduction which could be obtained for the experimental equipment, the numerical simulation shows that on a large scale, a reduction of 30 dB could be obtained. Also, measurement of power transmission intensity in a cylinder using two accelerometers was investigated. The results indicate a means of simplifying power transmission measurements in large cylindrical structures.