An ultrasonic reactor system with an appropriately designed reactor chamber used in conjunction with a compatible ultrasonic Barbell Horn or its derivative that provides a significant efficiency increase and an intensification of sonochemical and sonomechanical processes is disclosed. These enhancements arise from the ability of the reactor chamber to direct all treated liquid media through the highly active ultrasonic cavitation region located near the surface of the horn, as well as from several improvements in the Barbell Horn design that significantly increase its longevity and in its output surface area, thereby increasing the total size of the active cavitation region.