Technical devices are generally considered to be compliant instruments that are fully controllable tools, and from this perspective, humans have total power to operate machines at will. However, technologies often act back on humans, reversing the intended command direction. The Acoustic Chase project examines processes in which machines are intentionally provided with �degrees of freedom� not fully controllable by people. This will partially invert the relationship of human and tool, and create a system of balanced power. Expanding on the Haptic Opposition project, which combined touch and vision to create a human-machine interaction wherein the apparatuses could push back against human motion, Acoustic Chase will extend the concept of machines with a �free� acting will, but use sound as the primary output. The sensation of sound is direct; it offers quick information flow and a great variety of expressions. It is also difficult to escape: people can�t "hear away" or "close their ears." Tracking human body movements will provide an input channel. In combination with spatial sound, Acoustic Chase will enable intuitive human reactions, like discovering, playing, or fleeing.